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Red Hat JBoss Fuse
Deploying application packages into the Apache Karaf container
Version 6.3
Copyright © 2011-2020 Red Hat, Inc. and/or its affiliates.
26 Oct 2020
Abstract
The guide describes the options for deploying applications into a Red Hat JBoss Fuse container.
Part I. The Red Hat JBoss Fuse Container
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Abstract
The Red Hat JBoss Fuse container is a flexible container that supports a variety of different deployment models: OSGi bundle deployment and WAR deployment. The container is also integrated with Apache Maven, so that required artifacts can be downloaded and installed dynamically at deploy time.
Chapter 1. Red Hat JBoss Fuse Overview
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Abstract
Red Hat JBoss Fuse is a flexible container that allows you to deploy applications in a range of different package types (WAR or OSGi bundle) and has support for both synchronous and asynchronous communication.
1.1. Red Hat JBoss Fuse Container Architecture
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Overview
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Figure 1.1, “Red Hat JBoss Fuse Container Architecture” shows a high-level overview of the Red Hat JBoss Fuse container architecture, showing the variety of deployment models that are supported.
Figure 1.1. Red Hat JBoss Fuse Container Architecture
Deployment models
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Red Hat JBoss Fuse is a multi-faceted container that supports a variety of deployment models. You can deploy any of the following kinds of deployment unit:
- OSGi bundle
- An OSGi bundle is a JAR file augmented with metadata in the JAR's
META-INF/MANIFEST.MFfile. Because the Red Hat JBoss Fuse container is fundamentally an OSGi container, the OSGi bundle is also the native format for the container. Ultimately, after deployment, all of the other deployment unit types are converted into OSGi bundles. - WAR
- A Web application ARchive (WAR) is the standard archive format for applications that run inside a Web server. As originally conceived by the Java servlet specification, a WAR packages Web pages, JSP pages, Java classes, servlet code, and so on, as required for a typical Web application. More generally, however, a WAR can be any deployment unit that obeys the basic WAR packaging rules (which, in particular, require the presence of a Web application deployment descriptor,
web.xml).
Spring framework
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The Spring framework is a popular dependency injection framework, which is fully integrated into the JBoss Fuse container. In other words, Spring enables you to create instances of Java objects and wire them together by defining a file in XML format. In addition, you can also access a wide variety of utilities and services (such as security, persistence, and transactions) through the Spring framework.
Blueprint framework
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The blueprint framework is a dependency injection framework defined by the OSGi Alliance. It is similar to Spring (in fact, it was originally sponsored by SpringSource), but is a more lightweight framework that is optimized for the OSGi environment.
OSGi core framework
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At its heart, Red Hat JBoss Fuse is an OSGi container, based on Apache Karaf, whose architecture is defined by the OSGi Service Platform Core Specification (available from http://www.osgi.org/Release4/Download). OSGi is a flexible and dynamic container, whose particular strengths include: sophisticated management of version dependencies; sharing libraries between applications; and support for dynamically updating libraries at run time (hot fixes).
For more details about the OSGi framework, see Chapter 5, Introduction to OSGi.
Red Hat JBoss Fuse kernel
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The JBoss Fuse kernel extends the core framework of OSGi, adding features such as the runtime console, administration, logging, deployment, provisioning, management, and so on. For more details, see Section 5.1, “Red Hat JBoss Fuse”.
1.2. Deployment Models
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Overview
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Although Red Hat JBoss Fuse is an OSGi container at heart, it supports a variety of different deployment models. You can think of these as virtual containers, which hide the details of the OSGi framework. In this section we compare the deployment models to give you some idea of the weaknesses and strengths of each model.
Table 1.1, “Alternative Deployment Packages” shows an overview of the package types associated with each deployment model.
| Package | Metadata | Maven Plug-in | URI Scheme | File Suffix |
|---|---|---|---|---|
| Bundle | MANIFEST.MF | maven-bundle-plugin | None | .jar |
| WAR | web.xml | maven-war-plugin | war: | .war |
OSGi bundle deployment model
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Figure 1.2, “Installing an OSGi Bundle” gives an overview of what happens when you install an OSGi bundle into the Red Hat JBoss Fuse container, where the bundle depends on several other bundles.
Figure 1.2. Installing an OSGi Bundle
Implicitly, a bundle shares all of its dependencies. This is a flexible approach to deployment, which minimizes resource consumption. But it also introduces a degree of complexity when working with large applications. A bundle does not automatically load all of its requisite dependencies, so a bundle might fail to resolve, due to missing dependencies. The recommended way to remedy this is to use features to deploy the bundle together with its dependencies (see Chapter 8, Deploying Features).
WAR deployment model
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Figure 1.3, “Installing a WAR” gives an overview of what happens when you install a WAR into the JBoss Fuse container.
Figure 1.3. Installing a WAR
The WAR has a relatively simple deployment model, because the WAR is typically packaged together with all of its dependencies. Hence, the container usually does not have to do any work to resolve the WAR's dependencies. The drawback of this approach, however, is that the WAR is typically large and it duplicates libraries already available in the container (thus consuming more resources).
1.3. Dependency Injection Frameworks
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Dependency injection
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Dependency injection or inversion of control (IOC) is a design paradigm for initializing and configuring applications. Instead of writing Java code that explicitly finds and sets the properties and attributes required by an object, you declare setter methods for all of the properties and objects that this object depends on. The framework takes responsibility for injecting dependencies and properties into the object, using the declared setter methods. This approach reduces dependencies between components and reduces the amount of code that must be devoted to retrieving configuration properties.
There are many popular dependency injection frameworks in current use. In particular, the Spring framework and the blueprint framework are fully integrated with Red Hat JBoss Fuse.
OSGi framework extensions
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One of the important characteristics of the OSGi framework is that it is extensible. OSGi provides a framework extension API, which makes it possible to implement OSGi plug-ins that are tightly integrated with the OSGi core. An OSGi extension can be deployed into the OSGi container as an extension bundle, which is a special kind of bundle that enjoys privileged access to the OSGi core framework.
Red Hat JBoss Fuse defines extension bundles to integrate the following dependency injection frameworks with OSGi:
- Blueprint—the blueprint extensor is based on the blueprint implementation from Apache Karaf.
- Spring—the Spring extensor is based on Spring Dynamic Modules (Spring-DM), which is the OSGi integration component from SpringSource.NoteThe Spring-DM module is now deprecated. If you need an injection framework with OSGi integration, use Blueprint instead.
Activating a framework
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The framework extension mechanism enables both the Spring extensor and the blueprint extensor to be integrated with the bundle lifecycle. In particular, the extenders receive notifications whenever a bundle is activated (using the command,
osgi:start) or de-activated (using the command, osgi:stop). This gives the extenders a chance to scan the bundle, look for configuration files of the appropriate type and, if necessary, activate the dependency injection framework for that bundle.
For example, when we use Spring configuration, the spring extensor scans the bundle package, looking for any blueprint XML files in the standard location and, if it finds one or more such files, it activates the blueprint framework for this bundle.
Blueprint XML file location
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The blueprint extensor searches a bundle for blueprint XML files whose location matches the following pattern:
OSGI-INF/blueprint/*.xml
OSGI-INF/blueprint/*.xmlNote
A blueprint XML file can also be placed in a non-standard location, by specifying the location in a bundle header (see the section called “Custom Blueprint file locations”).
Spring XML file location
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The Spring extensor searches a bundle for Spring XML files whose location matches the following pattern:
META-INF/spring/*.xml
META-INF/spring/*.xmlNote
A WAR package uses a different mechanism to specify the location of Spring XML files (see Section 11.3, “Bootstrapping a Spring Context in a WAR”).
1.4. Synchronous Communication
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Overview
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Synchronous communication between bundles in the OSGi container is realized by publishing a Java object as an OSGi service. Clients of the OSGi service can then invoke the methods of the published object.
OSGi services
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An OSGi service is a plain Java object, which is published to make it accessible to other bundles deployed in the OSGi container. Other bundles then bind to the Java object and invoke its methods synchronously, using the normal Java syntax. OSGi services thus support a model of synchronous communication between bundles.
One of the strengths of this model is that the OSGi service is a perfectly ordinary Java object. The object is not required to inherit from specific interfaces nor is it required to have any annotations. In other words, your application code is not polluted by the OSGi deployment model.
OSGi registry
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To publish an OSGi service, you must register it in the OSGi registry. The OSGi specification defines a Java API for registering services, but the simplest way to publish an OSGi service is to exploit the special syntax provided by the blueprint framework. Use the blueprint
service element to register a Java object in the OSGi registry. For example, to create a SavingsAccountImpl object and export it as an OSGi service (exposing it through the org.fusesource.example.Account Java interface)
Another bundle in the container can then bind to the published OSGi service, by defining a blueprint
reference element that searches the OSGi registry for a service that supports the org.fusesource.example.Account interface.
For more details, see Section 16.1.2, “Defining a Service Bean”.
Note
Spring XML also supports the publication and binding of OSGi services.
Dynamic interaction between bundles
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Another important feature of OSGi services is that they are tightly integrated with the bundle lifecycle. When a bundle is activated (for example, using the console command,
osgi:start), its OSGi services are published to the OSGi registry. And when a bundle is de-activated (for example, using the console command, osgi:stop), its OSGi services are removed from the OSGi registry. Clients of a service can elect to receive notifications whenever a service is published to or removed from the OSGi registry.
Consequently, the presence or absence of an OSGi service in the registry can serve as a flag that signals to other bundles whether or not a particular bundle is available (active). With appropriate programming, clients can thus be implemented to respond flexibly as other bundles are uninstalled and re-installed in the container. For example, a client could be programmed to suspend certain kinds of processing until a bundle is re-activated, thus facilitating dynamic reconfiguration or updating of that dependent bundle.
1.5. Asynchronous Communication
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JMS broker
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You can optionally install a broker instance, typically Apache ActiveMQ, into the Red Hat JBoss Fuse container, to provide support for asynchronous communication between bundles in the container. Apache ActiveMQ is a sophisticated implementation of a JMS broker, which supports asynchronous communication using either queues or topics (publish-subscribe model). Some of the basic features of this JMS broker are as follows:
- VM protocol—the Virtual Machine (VM) transport protocol is ideal for communicating within the container. VM is optimized for sending messages within the same JVM instance.
- Persistent or non-persistent messaging—you can choose whether the broker should persist messages or not, depending on the requirements of your application.
- Ease of use—there is no need to create and configure destinations (that is, queues or topics) before you can use them. After connecting to a broker, you can immediately start sending and receiving messages. If you start sending messages to a queue that does not exist yet, Apache ActiveMQ creates it dynamically.
- External communication—you can also configure a TCP port on the broker, opening it up to external JMS clients or other brokers.
For details of how to set up a JMS broker in Red Hat JBoss Fuse, see Chapter 17, JMS Broker.
1.6. Fuse Fabric
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Overview
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Fuse Fabric is a technology layer that allows a group of containers to form a cluster that shares a common set of configuration information and a common set of repositories from which to access runtime artifacts. Fabric containers are managed by a Fabric Agent that installs a set of bundles that are specified in the profiles assigned to the container. The agent requests artifacts from the Fabric Ensemble. The ensemble has a list of repositories that it can access. These repositories are managed using a Maven proxy and include a repository that is local to the ensemble.
The added layer imposed on fabric containers does not change the basic deployment models, but it does impact how you specify what needs to be deployed. It also impacts how dependencies are located.
Bundle deployment
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In a fabric container, you cannot directly deploy bundles to a container. A container's configuration is managed by a Fabric Agent that updates its contents and configuration based on one or more profiles. So to add a bundle to a container, you must either add the bundle to an existing profile or create a new profile containing the bundle. When the profile is applied to a container the Fuse Agent will install the bundle.
The installation process will download the bundle from a Maven repository and use the appropriate install command to load it into the container. Once the bundle is installed, the dependency resolution process proceeds as it would in a standalone container.
Things to consider
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While installing bundles to a fabric container is not radically different from installing bundles in a standalone container, there are a number of things to consider when thinking about creating profiles to deploy your applications:
- Bundles must be accessible through the fabric's Maven proxyWhen a Fabric Agent installs a bundle, it must first copy the bundle to the container's host computer. To do so, the agent uses the fabric's Maven Proxy to locate the bundle in one of the accessible Maven repositories and downloads it. This mechanism ensures that all of the containers in the fabric have access to the same set of bundles.To address this issue, you need to ensure that the fabric's Maven proxy is configured to have access to all of the repositories from which your applications will need to download bundles. For more information see section "Configuring Maven Proxies Directly" in "Fabric Guide".
- Fabric Agents only load the bundles specified in a profileA fabric container's contents is completely controlled by the profiles associated with it. The fabric agent managing the container inspects each of the profiles associated with the container, downloads the listed bundles, and features, and installs them. If one of the bundles in a profile depends on a bundle that is not specified in the profile, or one of the other profiles associated with the container, the bundle will not be able to resolve that dependency.To address this issue you can do one of the following:
- construct your profiles to ensure that it contains all of the required bundles and their dependencies
- deploy the application as a feature that contains all of the required bundles and their dependencies
Chapter 2. Dependency Injection Frameworks
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Abstract
Red Hat JBoss Fuse supports two alternative dependency injection frameworks: Spring and OSGi blueprint. These frameworks are fully integrated with the Red Hat JBoss Fuse container, so that Spring XML files and blueprint XML files are automatically activated at the same time the corresponding bundle is activated.
2.1. Spring and Blueprint Frameworks
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Overview
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The OSGi framework allows third-party frameworks to be piggybacked on top of it. In particular, Red Hat JBoss Fuse enables the Spring framework and the blueprint framework, by default. In the case of the Spring framework, OSGi automatically activates any Spring XML files under the
META-INF/spring/ directory in a JAR, and Spring XML files can also be hot-deployed to the ESBInstallDir/deploy directory. In the case of the blueprint framework, OSGi automatically activates any blueprint XML files under the OSGI-INF/blueprint/ directory in a JAR, and blueprint XML files can also be hot-deployed to the ESBInstallDir/deploy directory.
Prefer Blueprint over Spring-DM
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The Blueprint container is now the preferred framework for instantiating, registering, and referencing OSGi services, because this container has now been adopted as an OSGi standard. This ensures greater portability for your OSGi service definitions in the future.
Spring Dynamic Modules (Spring-DM) provided much of the original impetus for the definition of the Blueprint standard, but should now be regarded as obsolescent. Using the Blueprint container does not prevent you from using the Spring framework: the latest version of Spring is compatible with Blueprint.
Configuration files
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There are two kinds of file that you can use to configure your project:
- Spring configuration—in the standard Maven directory layout, Spring XML configuration files are located under
ProjectDir/src/main/resources/META-INF/spring. - Blueprint configuration—in the standard Maven directory layout, blueprint XML configuration files are located under
ProjectDir/src/main/resources/OSGI-INF/blueprint.
If you decide to use the blueprint configuration, you can embed
camelContext elements in the blueprint file, as described in the section called “Blueprint configuration file”.
Prerequisites for blueprint configuration
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If you decide to configure your Apache Camel application using blueprint, you must ensure that the
camel-blueprint feature is installed. If necessary, install it by entering the following console command:
JBossFuse:karaf@root> features:install camel-blueprint
JBossFuse:karaf@root> features:install camel-blueprintSpring configuration file
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You can deploy a
camelContext using a Spring configuration file, where the root element is a Spring beans element and the camelContext element is a child of the beans element. In this case, the camelContext namespace must be http://camel.apache.org/schema/spring.
For example, the following Spring configuration defines a route that generates timer messages every two seconds, sending the messages to the
ExampleRouter log (which get incorporated into the console log file, InstallDir/data/log/fuse.log):
It is not necessary to specify schema locations in the configuration. But if you are editing the configuration file with an XML editor, you might want to add the schema locations in order to support schema validation and content completion in the editor. For the preceding example, you could specify the schema locations as follows:
Blueprint configuration file
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Before deploying routes in a blueprint configuration file, check that the camel-blueprint feature is already installed.
You can deploy a
camelContext using a blueprint configuration file, where the root element is blueprint and the camelContext element is a child of the blueprint element. In this case, the camelContext namespace must be http://camel.apache.org/schema/blueprint.
For example, the following blueprint configuration defines a route that generates timer messages every two seconds, sending the messages to the
ExampleRouter log (which get incorporated into the console log file, InstallDir/data/log/fuse.log):
Note
Blueprint is a dependency injection framework, defined by the OSGi standard, which is similar to Spring in many respects. For more details about blueprint, see Section 16.1, “The Blueprint Container”.
2.2. Hot Deployment
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Types of configuration file
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You can hot deploy the following types of configuration file:
- Spring XML file, deployable with the suffix,
.xml. - Blueprint XML file, deployable with the suffix,
.xml.
Hot deploy directory
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If you have an existing Spring XML or blueprint XML configuration file, you can deploy the configuration file directly by copying it into the following hot deploy directory:
InstallDir/deploy
InstallDir/deploy
After deploying, the configuration file is activated immediately.
Hot undeploying an XML file
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To undeploy a Spring XML file or a Blueprint XML file from the hot deploy directory, simply delete the XML file from the
InstallDir/deploy directory while the Apache Karaf container is running.
Important
The hot undeploy mechanism does not work while the container is shut down. If you shut down the Karaf container, delete the XML file from
deploy/, and then restart the Karaf container, the automatically generated bundle corresponding to the XML file will not be undeployed after you restart the container (you can, however, undeploy the bundle manually using the osgi:uninstall console command).
Prerequisites
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If you want to deploy Apache Camel routes in a blueprint configuration file, the
camel-blueprint feature must be installed (which it is by default). If the camel-blueprint feature has been disabled, however, you can re-install it by entering the following console command:
JBossFuse:karaf@root> features:install camel-blueprint
JBossFuse:karaf@root> features:install camel-blueprintDefault bundle version
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When a Spring XML file or a Blueprint XML file is hot deployed, the XML file is automatically wrapped in an OSGi bundle and deployed as a bundle in the OSGi container. By default, the generated bundle has the version,
0.0.0.
Customizing the bundle version
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If you prefer to customize the bundle version, use the
manifest element in the XML file. The manifest element enables you to override any of the headers in the generated bundle's META-INF/MANIFEST.MF file. In particular, you can use it to specify the bundle version.
Specifying the bundle version in a Spring XML file
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To specify the bundle version in a hot-deployed Spring XML file, define a
manifest element as follows:
The
manifest element for Spring XML files belongs to the following schema namespace:
http://karaf.apache.org/xmlns/deployer/spring/v1.0.0
http://karaf.apache.org/xmlns/deployer/spring/v1.0.0
The contents of the
manifest element are specified using the syntax of a Java properties file.
Specifying the bundle version in a Blueprint XML file
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To specify the bundle version in a hot-deployed Blueprint XML file, define a
manifest element as follows:
The
manifest element for Blueprint XML files belongs to the following schema namespace:
http://karaf.apache.org/xmlns/deployer/blueprint/v1.0.0
http://karaf.apache.org/xmlns/deployer/blueprint/v1.0.0
The contents of the
manifest element are specified using the syntax of a Java properties file.
2.3. Using OSGi Configuration Properties
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Overview
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The OSGi Configuration Admin service defines a mechanism for passing configuration settings to an OSGi bundle. You do not have to use this service for configuration, but it is typically the most convenient way of configuring applications deployed in Red Hat JBoss Fuse.
Persistent ID
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In the OSGi Configuration Admin service, a persistent ID is a name that identifies a group of related configuration properties. In JBoss Fuse, every persistent ID, PersistentID, is implicitly associated with a file named
PersistentID.cfg in the ESBInstallDir/etc/ directory. If the corresponding file exists, it can be used to initialize the values of properties belonging to the PersistentID property group.
For example, the
etc/org.ops4j.pax.url.mvn.cfg file is used to set the properties associated with the org.ops4j.pax.url.mvn persistent ID (for the PAX Mvn URL handler).
Blueprint example
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Example 2.1, “Using OSGi Configuration Properties in Blueprint” shows how to pass the value of the
prefix variable to the constructor of the myTransform bean in blueprint XML, where the value of prefix is set by the OSGi Configuration Admin service.
Example 2.1. Using OSGi Configuration Properties in Blueprint
The syntax,
{{prefix}}, substitutes the value of the prefix variable into the blueprint XML file. The OSGi properties are set up using the following XML elements:
cm:property-placeholder- This element gives you access to the properties associated with the specified persistent ID. After defining this element, you can use the syntax,
{{PropName}}, to substitute variables belonging to the specified persistent ID. cm:property-placeholder/cm:default-properties- You can optionally specify default values for properties by defining
cm:propertyelements inside thecm:default-propertieselement. If the correspondingetc/PersistentID.cfgfile defines property values, however, these will be used instead.
Using multiple property placeholders in Blueprint
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It is legal to define multiple property placeholders in a Blueprint XML file (that is, defining multiple
cm:property-placeholder elements that reference different persistent IDs). One thing that you need to be aware of, however, is that there can be a clash if two properties from different property placeholders have the same name. In this case, the following rules determine which property takes precedence:
- Explicitly defined property settings (for example, defined in a
etc/PersistentID.cfgfile) take precedence over default property settings (defined in acm:default-propertieselement). - If there is more than one explicit setting for a given property, the setting from the last property placeholder in the Blueprint file takes precedence.
- Default property settings (defined in a
cm:default-propertieselement) have the lowest priority.
Chapter 3. Building with Maven
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Abstract
Maven is an open source build system which is available from the Apache Maven project. This chapter explains some of the basic Maven concepts and describes how to set up Maven to work with Red Hat JBoss Fuse. In principle, you could use any build system to build an OSGi bundle. But Maven is strongly recommended, because it is well supported by Red Hat JBoss Fuse.
3.1. Maven Directory Structure
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Overview
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One of the most important principles of the Maven build system is that there are standard locations for all of the files in the Maven project. There are several advantages to this principle. One advantage is that Maven projects normally have an identical directory layout, making it easy to find files in a project. Another advantage is that the various tools integrated with Maven need almost no initial configuration. For example, the Java compiler knows that it should compile all of the source files under
src/main/java and put the results into target/classes.
Standard directory layout
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Example 3.1, “Standard Maven Directory Layout” shows the elements of the standard Maven directory layout that are relevant to building OSGi bundle projects. In addition, the standard locations for Spring and Blueprint configuration files (which are not defined by Maven) are also shown.
Example 3.1. Standard Maven Directory Layout
Note
It is possible to override the standard directory layout, but this is not a recommended practice in Maven.
pom.xml file
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The
pom.xml file is the Project Object Model (POM) for the current project, which contains a complete description of how to build the current project. A pom.xml file can be completely self-contained, but frequently (particular for more complex Maven projects) it can import settings from a parent POM file.
After building the project, a copy of the
pom.xml file is automatically embedded at the following location in the generated JAR file:
META-INF/maven/groupId/artifactId/pom.xml
META-INF/maven/groupId/artifactId/pom.xmlsrc and target directories
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The
src/ directory contains all of the code and resource files that you will work on while developing the project.
The
target/ directory contains the result of the build (typically a JAR file), as well as all all of the intermediate files generated during the build. For example, after performing a build, the target/classes/ directory will contain a copy of the resource files and the compiled Java classes.
main and test directories
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The
src/main/ directory contains all of the code and resources needed for building the artifact.
The
src/test/ directory contains all of the code and resources for running unit tests against the compiled artifact.
java directory
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Each
java/ sub-directory contains Java source code (*.java files) with the standard Java directory layout (that is, where the directory pathnames mirror the Java package names, with / in place of the . character). The src/main/java/ directory contains the bundle source code and the src/test/java/ directory contains the unit test source code.
resources directory
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If you have any configuration files, data files, or Java properties to include in the bundle, these should be placed under the
src/main/resources/ directory. The files and directories under src/main/resources/ will be copied into the root of the JAR file that is generated by the Maven build process.
The files under
src/test/resources/ are used only during the testing phase and will not be copied into the generated JAR file.
Spring integration
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By default, Red Hat JBoss Fuse installs and activates support for Spring Dynamic Modules (Spring DM), which integrates Spring with the OSGi container. This means that it is possible for you to include Spring configuration files,
META-INF/spring/*.xml, in your bundle. One of the key consequences of having Spring DM enabled in the OSGi container is that the lifecycle of the Spring application context is automatically synchronized with the OSGi bundle lifecycle:
- Activation—when a bundle is activated, Spring DM automatically scans the bundle to look for Spring configuration files in the standard location (any
.xmlfiles found under theMETA-INF/spring/directory). If any Spring files are found, Spring DM creates an application context for the bundle and creates the beans defined in the Spring configuration files. - Stopping—when a bundle is stopped, Spring DM automatically shuts down the bundle's Spring application context, causing any Spring beans to be deleted.
In practice, this means that you can treat your Spring-enabled bundle as if it is being deployed in a Spring container. Using Spring DM, the features of the OSGi container and a Spring container are effectively merged. In addition, Spring DM provides additional features to support the OSGi container environment—some of these features are discussed in Chapter 16, OSGi Services.
Blueprint container
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OSGi R4.2 defines a blueprint container, which is effectively a standardized version of Spring DM. Red Hat JBoss Fuse has built-in support for the blueprint container, which you can enable simply by including blueprint configuration files,
OSGI-INF/blueprint/*.xml, in your project. For more details about the blueprint container, see Chapter 16, OSGi Services.
3.2. Preparing to use Maven
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Overview
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This section gives a brief overview of how to prepare Maven for building Red Hat JBoss Fuse projects and introduces the concept of Maven coordinates, which are used to locate Maven artifacts.
Prerequisites
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In order to build a project using Maven, you must have the following prerequisites:
- Maven installation—Maven is a free, open source build tool from Apache. You can download the latest version from the Maven download page.
- Network connection—whilst performing a build, Maven dynamically searches external repositories and downloads the required artifacts on the fly. By default, Maven looks for repositories that are accessed over the Internet. You can change this behavior so that Maven will prefer searching repositories that are on a local network.NoteMaven can run in an offline mode. In offline mode Maven will only look for artifacts in its local repository.
Adding the Red Hat JBoss Fuse repository
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In order to access artifacts from the Red Hat JBoss Fuse Maven repository, you need to add it to Maven's
settings.xml file. Maven looks for your settings.xml file in the .m2 directory of the user's home directory. If there is not a user specified settings.xml file, Maven will use the system-level settings.xml file at M2_HOME/conf/settings.xml.
To add the JBoss Fuse repository to Maven's list of repositories, you can either create a new
.m2/settings.xml file or modify the system-level settings. In the settings.xml file, add the repository element for the JBoss Fuse repository as shown in bold text in Example 3.2, “Adding the Red Hat JBoss Fuse Repositories to Maven”.
Example 3.2. Adding the Red Hat JBoss Fuse Repositories to Maven
Artifacts
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The basic building block in the Maven build system is an artifact. The output of an artifact, after performing a Maven build, is typically an archive, such as a JAR or a WAR.
Maven coordinates
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A key aspect of Maven functionality is the ability to locate artifacts and manage the dependencies between them. Maven defines the location of an artifact using the system of Maven coordinates, which uniquely define the location of a particular artifact. A basic coordinate tuple has the form,
{groupId, artifactId, version}. Sometimes Maven augments the basic set of coordinates with the additional coordinates, packaging and classifier. A tuple can be written with the basic coordinates, or with the additional packaging coordinate, or with the addition of both the packaging and classifier coordinates, as follows:
groupdId:artifactId:version groupdId:artifactId:packaging:version groupdId:artifactId:packaging:classifier:version
groupdId:artifactId:version
groupdId:artifactId:packaging:version
groupdId:artifactId:packaging:classifier:version
Each coordinate can be explained as follows:
- groupdId
- Defines a scope for the name of the artifact. You would typically use all or part of a package name as a group ID—for example,
org.fusesource.example. - artifactId
- Defines the artifact name (relative to the group ID).
- version
- Specifies the artifact's version. A version number can have up to four parts:
n.n.n.n, where the last part of the version number can contain non-numeric characters (for example, the last part of1.0-SNAPSHOTis the alphanumeric substring,0-SNAPSHOT). - packaging
- Defines the packaged entity that is produced when you build the project. For OSGi projects, the packaging is
bundle. The default value isjar. - classifier
- Enables you to distinguish between artifacts that were built from the same POM, but have different content.
The group ID, artifact ID, packaging, and version are defined by the corresponding elements in an artifact's POM file. For example:
For example, to define a dependency on the preceding artifact, you could add the following
dependency element to a POM:
Note
It is not necessary to specify the
bundle package type in the preceding dependency, because a bundle is just a particular kind of JAR file and jar is the default Maven package type. If you do need to specify the packaging type explicitly in a dependency, however, you can use the type element.
Chapter 4. Locating Artifacts with Maven and HTTP
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Abstract
In Red Hat JBoss Fuse, Maven is the primary mechanism for locating artifacts and dependencies, both at build time and at run time. Normally, Maven requires Internet connectivity, so that dependencies can be downloaded from remote repositories on demand. But, as explained here, it is also possible to provide dependencies locally, so that the need for Internet connectivity is reduced.
4.1. Locating HTTP Artifacts
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Overview
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You can specify the location of an OSGi bundle (and other kinds of resource) using a HTTP URL—for example, by specifying a HTTP URL as the argument to the
osgi:install command. This approach is perhaps not as common as using Maven URLs, but it means that you have the option of providing OSGi resources through a Web server.
HTTP URL protocol
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The HTTP URL protocol specifies the location of an OSGi bundle (or other resource) using a standard HTTP (or HTTPS) URL. Typically, a HTTP URL has a syntax like the following:
http[s]:Host[:Port]/[Path][#AnchorName][?Query]
http[s]:Host[:Port]/[Path][#AnchorName][?Query]
In a standalone (non-Fabric) container, a HTTP URL lookup can be triggered by either of the following events:
- When
osgi:installis invoked on a Maven URL to install an OSGi bundle; - When
features:installis invoked to install a Karaf feature (a Karaf feature typically includes one or more Maven URL references).
HTTP URL handler
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JBoss Fuse uses Java's built-in HTTP protocol handler to resolve HTTP URLs. Hence, HTTP URL resolution behaves exactly as you would expect in standard Java.
Karaf bundle cache
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When you pass a HTTP URL as the argument to the
osgi:install command (or embedded in a Karaf feature description), JBoss Fuse downloads the referenced OSGi bundle resource, saves it in the Karaf bundle cache (under the data/cache directory), and loads the bundle into the Karaf container runtime. The Karaf bundle cache is used to persist all of the bundles currently installed in the Karaf runtime.
Note
When a Karaf container is stopped and restarted, it loads its installed bundles directly from the Karaf bundle cache, not from the local Maven repository (or anywhere else). Hence, if you have updated any artifacts in the local Maven repository in the meantime, those changes are not automatically reflected in the state of the Karaf container.
Configuring a HTTP proxy for HTTP URLs
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To configure a HTTP proxy (which will be used when resolving HTTP URLs), open the
InstallDir/etc/system.properties file in a text editor and set the http.proxyHost and http.proxyPort system properties with the host and port of the proxy—for example:
http.proxyHost=192.0.2.0 http.proxyPort=8080
http.proxyHost=192.0.2.0
http.proxyPort=8080
You can optionally specify a list of non-proxy hosts (hosts that can be reached without going through the proxy) using the
http.nonProxyHosts property—for example:
http.nonProxyHosts=localhost|*.redhat.com|*.jboss.org
http.nonProxyHosts=localhost|*.redhat.com|*.jboss.orgNote
An advantage of using the system properties approach to configuring the proxy is that these settings will be used both by the
mvn URL protocol handler and by the http URL protocol handler (see the section called “Configuring a HTTP proxy for Maven URLs”).
4.2. Locating Maven Artifacts at Build Time
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Overview
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When building projects, Maven implements a simple caching scheme: artifacts are downloaded from remote repositories on the Internet and then cached in the local repository. Figure 4.1, “How Maven Locates Artifacts at Build Time” shows an overview of the procedure that Maven follows when locating artifacts at build time.
Figure 4.1. How Maven Locates Artifacts at Build Time
Locating artifacts at build time
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While building a project, Maven locates required artifacts (OSGi bundles, Karaf features, required plug-ins, and so on) as follows:
- The first place that Maven looks for artifacts is in the local repository,
~/.m2/repository/(which is effectively a cache where Maven stores the artifacts it has already downloaded or found elsewhere). - If an artifact is not available in the local repository, Maven attempts to download the artifact from one of the repositories listed in its configuration. This repository list can include both internal and remote repositories.
- If the artifact is not available from an internal repository, the next repositories to try are the remote repositories (accessible through HTTP or HTTPS).
- When a Maven project is built locally using the
mvn installcommand, the project's Maven artifacts are installed into the local repository.
Adding a remote Maven repository
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Remote repositories are configured in the same way as internal repositories, except that they should be listed after any internal repositories.
Adding an internal Maven repository
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Maven enables you to specify the location of internal repositories either in your
settings.xml file (which applies to all projects) or in a pom.xml (which applies to that project only). Typically, the location of an internal repository is specified using either a file:// URL or a http:// URL (assuming you have set up a local Web server to serve up the artifacts) and you should generally ensure that internal repositories are listed before remote repositories. Otherwise, there is nothing special about an internal repository: it is just a repository that happens to be located in your internal network.
For an example of how to specify a repository in your
settings.xml file, see the section called “Adding the Red Hat JBoss Fuse repository”.
Customizing the location of the local repository
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Maven resolves the location of the local repository, by checking the following settings:
- The location specified by the
localRepositoryelement in the~/.m2/settings.xmlfile (UNIX and Linux) orC:\Documents and Settings\UserName\.m2\settings.xml(Windows). - Otherwise, the location specified by the
localRepositoryelement in theM2_HOME/conf/settings.xmlfile. - Otherwise, the default location is in the user's home directory,
~/.m2/repository/(UNIX and Linux) orC:\Documents and Settings\UserName\.m2\repository(Windows).
4.3. Locating Maven Artifacts at Run Time
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Abstract
At run time, the process of locating Maven artifacts is implemented by the Eclipse Aether library, which is bundled with the Karaf container (so that it is not necessary for Apache Maven to be installed on the container host). It is possible to customize the Karaf container's Maven configuration by editing the
etc/org.ops4j.pax.url.mvn.cfg file. For example, you can customize the list of remote Maven repositories and you can configure a HTTP proxy, if required.
4.3.1. Maven URL Handler Architecture
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Overview
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You can specify the location of an OSGi bundle using a Maven URL—for example, as the argument to the
osgi:install command. When resolution of a Maven URL is triggered, JBoss Fuse uses a combination of the Pax URL Aether component and the Eclipse Aether component to implement artifact resolution. The basic strategy is to search the system/ directory, then search the local Maven repository, and then search the configured remote Maven repositories.
Maven URL protocol
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The Maven URL protocol specifies the location of a Maven artifact, which can be retrieved either from local or remote Maven repositories. For example, an artifact with the Maven coordinates,
GroupId:ArtifactId:Version, can be referenced by the following Maven URL:
mvn:GroupId/ArtifactId/Version
mvn:GroupId/ArtifactId/Version
In a standalone (non-Fabric) container, a Maven URL lookup can be triggered by either of the following events:
- When
osgi:installis invoked on a Maven URL to install an OSGi bundle; - When
features:installis invoked to install a Karaf feature (a Karaf feature typically includes one or more Maven URL references).
Pax URL Aether layer
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In Apache Karaf, the framework for resolving Maven URLs is the URL protocol handler mechanism, which is a standard feature of the Java language and JVM. To handle URLs prefixed by the
mvn: scheme, Karaf registers the OPS4J Pax URL Aether protocol handler. The Pax URL Aether layer is thus responsible for resolving all mvn URLs in the JVM. This layer can be configured through one or both of the following configuration files:
InstallDir/etc/org.ops4j.pax.url.mvn.cfg- Stores the OSGi Config Admin properties used to configure the Pax URL Aether layer. In particular, it is possible to specify the locations of local and remote Maven repositories through the settings in this file. For details of the available settings, see Section 4.3.5, “Pax URL Aether Reference”.
UserHome/.m2/settings.xml- (Optional) You can optionally configure the Pax URL Aether layer to read its configuration from a standard Maven
settings.xmlfile (by configuring the relevant settings inorg.ops4j.pax.url.mvn.cfg).
The main purpose of the Pax URL Aether layer is to facilitate configuration. The Pax URL Aether layer does not actually implement resolution of Maven artifacts. That responsibility is delegated to the Eclipse Aether layer instead.
Note
In some old
org.ops4j.pax.url.mvn.cfg configuration files, you might see the setting disableAether=false. This setting is obsolete, however, and has no effect on the pax-url-aether component. The current implementation of Pax URL Aether (previously called Pax URL Maven) is completely dependent on Eclipse Aether.
Eclipse Aether layer
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The Eclipse Aether layer is fundamental to Maven artifact resolution in Apache Karaf. Ultimately, resolution of Maven artifacts for the Karaf container is always performed by the Aether layer. Note that the Aether layer itself is stateless: the parameters required to perform resolution of a Maven artifact are passed to the Aether layer with every invocation.
Locating artifacts at run time
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Figure 4.2, “How the Container Locates Artifacts at Run Time” shows the mechanism for handling a Maven URL and resolving a Maven artifact at run time.
Figure 4.2. How the Container Locates Artifacts at Run Time
The steps followed to locate the required Maven artifacts are:
- Resolution of a Maven artifact is triggered when a user invokes the
osgi:installcommand on a Maven URL (or if a user invokes thefeatures:installcommand on a feature that references some Maven URLs). - To resolve the Maven URL, the JVM calls back on the protocol handler registered against the
mvnscheme, which happens to be the Pax URL Aether component. - The Pax URL Aether component reads its configuration from the
InstallDir/etc/org.ops4j.pax.url.mvn.cfgfile (and possibly also from a Mavensettings.xmlfile, if so configured). The Pax URL Aether layer parses the requested Maven URL and combines this information with the specified configuration in order to invoke the Eclipse Aether library. - When the Aether library is invoked, the first step is to look up any local Maven repositories to try and find the Maven artifact. The following local repositories are configured by default:
InstallDir/system- The JBoss Fuse system directory, which contains all of the Maven artifacts that are bundled with the JBoss Fuse distribution.
UserHome/.m2/repository- The user's own local Maven repository in the user's home directory,
UserHome.
If you like, you can customize the list of local repositories to add your own custom Maven repository.If the Maven artifact is found locally, skip straight to step 7. - If the Maven artifact cannot be found in one of the local repositories, Aether tries to look up the specified remote repositories (using the list of remote repositories specified in the Pax URL Aether configuration). Because the remote repositories are typically located on the Internet (accessed through the HTTP protocol), it is necessary to have Internet access for this step to succeed.NoteIf your local network requires you to use a HTTP proxy to access the Internet, it is possible to configure Pax URL Aether to use a HTTP proxy. For example, see the section called “Configuring a HTTP proxy for Maven URLs” for details.
- If the Maven artifact is found in a remote repository, Aether automatically installs the artifact into the user's local Maven repository, so that another remote lookup will not be required.
- Finally, assuming that the Maven artifact has been successfully resolved, Karaf installs the artifact in the Karaf bundle cache,
InstallDir/data/cache, and loads the artifact (usually, an OSGi bundle) into the container runtime. At this point, the artifact is effectively installed in the container.
4.3.2. Redeploying Maven Artifacts in a Development Environment
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Overview
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An important aspect of the Karaf container architecture is that deployed Maven artifacts are stored in the container cache, which is separate from the local Maven repository. Bundles and features get copied from the local Maven repository into the cache at the time they are first deployed. After that, any changes to the artifact in the local Maven repository are ignored.
Immutable artifacts
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Usually, it makes sense to ignore changes in the local Maven repository, because Maven requires each specific version of an artifact to be immutable: that is, once you make a particular version of a Maven artifact available in a Maven repository, it must never change. Hence, it should never be necessary to go back and check the Maven repository for changes to the artifact.
SNAPSHOT artifacts
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On the other hand, there is a partial exception to this convention: in a development environment, the same artifacts are constantly being rebuilt and retested, which requires them to be redeployed into the Karaf container. The correct way to deal with this is to attach the suffix
-SNAPSHOT to the Maven version specifier. Maven treats these artifacts differently: for example, by periodically checking remote Maven repositories for updates and downloading the changed artifacts to the local repository.
Explicitly redeploying
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When working with SNAPSHOT artifacts, you will also need to redeploy the changed artifacts to the Karaf container. One approach is explicit redeployment.
For example, say you have already deployed the
org.example/myfoobundle/1.0.0-SNAPSHOT Maven artifact into the Karaf container and this bundle has the bundle ID, 751. If you now rebuild this bundle (for example, by executing mvn install in the bundle's Maven project), you can redeploy the changed bundle with the following console commands:
osgi:uninstall 751 osgi:install mvn:org.example/myfoobundle/1.0.0-SNAPSHOT
osgi:uninstall 751
osgi:install mvn:org.example/myfoobundle/1.0.0-SNAPSHOTdev:watch command
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Typically, a more convenient approach to redeploying SNAPSHOT artifacts is to enable automatic redeployment, using the
dev:watch command. For example, given a particular bundle—with bundle ID, 751—you can enable automatic redeployment by entering the command:
dev:watch 751
dev:watch 751
Now, whenever you rebuild and install the Maven artifact into your local Maven repository (for example, by executing
mvn install in your Maven project), the Karaf container automatically re-installs the changed Maven artifact. For more details, see section "dev:watch, watch" in "Console Reference".
Important
Using the
dev:watch command is intended for a development environment only. It is not recommended for use in a production environment.
4.3.3. Configuring Pax URL Aether Directly
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Overview
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The default approach to configuring the Pax URL Aether component is to edit the property settings in the
InstallDir/etc/org.ops4j.pax.url.mvn.cfg file directly. This approach is particularly convenient for a production environment, because the Maven configuration is colocated with the rest of the container configuration.
Note
In order to use the direct configuration approach, you must at least set the
org.ops4j.pax.url.mvn.repositories property. If this property is not set, Pax URL Aether falls back to reading configuration from the Maven settings.xml file.
Adding a remote Maven repository
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To add a remote Maven repository to the Pax URL Aether configuration, open the
InstallDir/etc/org.ops4j.pax.url.mvn.cfg configuration file in a text editor and edit the org.ops4j.pax.url.mvn.repositories property setting. The default is as follows:
org.ops4j.pax.url.mvn.repositories= \
http://repo1.maven.org/maven2@id=maven.central.repo, \
https://maven.repository.redhat.com/ga@id=redhat.ga.repo, \
https://maven.repository.redhat.com/earlyaccess/all@id=redhat.ea.repo, \
https://repository.jboss.org/nexus/content/groups/ea@id=fuseearlyaccess
org.ops4j.pax.url.mvn.repositories= \
http://repo1.maven.org/maven2@id=maven.central.repo, \
https://maven.repository.redhat.com/ga@id=redhat.ga.repo, \
https://maven.repository.redhat.com/earlyaccess/all@id=redhat.ea.repo, \
https://repository.jboss.org/nexus/content/groups/ea@id=fuseearlyaccess
Where the
org.ops4j.pax.url.mvn.repositories property is defined as a comma-separated list of Maven repository URLs. The backslash character, \, functions as a (UNIX style) line continuation character and must be followed immediately by the newline character. The Pax URL Aether component supports special repository URL options, defined using the @Option=Value syntax—see the section called “Pax URL Aether repository URL syntax”.
Note
The
@id option specifies the name of the repository and is required by the Aether layer.
Note
The presence of the
org.ops4j.pax.url.mvn.repositories property setting has an important side effect: it signals that the Pax URL Aether component takes its configuration from the etc/org.ops4j.pax.url.mvn.cfg, not from a settings.xml file (even if the org.ops4j.pax.url.mvn.settings property has been set).
Adding a default Maven repository
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The default repositories are a list of repositories that the container always checks first. To add a default Maven repository to the Pax URL Aether configuration, open the
InstallDir/etc/org.ops4j.pax.url.mvn.cfg configuration file in a text editor and edit the org.ops4j.pax.url.mvn.defaultRepositories property setting. The default is as follows:
org.ops4j.pax.url.mvn.defaultRepositories=\
file:${runtime.home}/${karaf.default.repository}@snapshots@id=karaf.${karaf.default.repository},\
file:${runtime.home}/local-repo@snapshots@id=karaf.local-repo,\
file:${karaf.base}/${karaf.default.repository}@snapshots@id=child.karaf.${karaf.default.repository}
org.ops4j.pax.url.mvn.defaultRepositories=\
file:${runtime.home}/${karaf.default.repository}@snapshots@id=karaf.${karaf.default.repository},\
file:${runtime.home}/local-repo@snapshots@id=karaf.local-repo,\
file:${karaf.base}/${karaf.default.repository}@snapshots@id=child.karaf.${karaf.default.repository}
Where the
org.ops4j.pax.url.mvn.defaultRepositories property is defined as a comma-separated list of Maven repository URLs. The backslash character, \, functions as a (UNIX style) line continuation character and must be followed immediately by the newline character. Local repositories should be defined using a URL with the file: scheme. The Pax URL Aether component supports special repository URL options, defined using the @Option=Value syntax—see the section called “Pax URL Aether repository URL syntax”.
Note
It is recommended that you leave the container's system repository as the first entry in the list.
Customizing the location of the local Maven repository
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The local Maven repository plays a special role, because it is the primary local cache of Maven artifacts: whenever Maven downloads an artifact from a remote repository, it installs the artifact into the local repository. The usual location of the local Maven repository is
.m2/repository/ under the user's home directory. You can optionally customize the location by setting the org.ops4j.pax.url.mvn.localRepository property in the InstallDir/etc/org.ops4j.pax.url.mvn.cfg configuration file. For example:
org.ops4j.pax.url.mvn.localRepository= /home/jbloggs/path/to/local/repository
org.ops4j.pax.url.mvn.localRepository= /home/jbloggs/path/to/local/repository
By default, this property is not set.
Configuring a HTTP proxy for Maven URLs
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To configure a HTTP proxy (which will be used when connecting to remote Maven repositories), open the
InstallDir/etc/system.properties file in a text editor and set the http.proxyHost and http.proxyPort system properties with the host and port of the proxy—for example:
http.proxyHost=192.0.2.0 http.proxyPort=8080
http.proxyHost=192.0.2.0
http.proxyPort=8080
You can optionally specify a list of non-proxy hosts (hosts that can be reached without going through the proxy) using the
http.nonProxyHosts property—for example:
http.nonProxyHosts=localhost|*.redhat.com|*.jboss.org
http.nonProxyHosts=localhost|*.redhat.com|*.jboss.orgNote
An advantage of using the system properties approach to configuring the proxy is that these settings will be used both by the
mvn URL protocol handler and by the http URL protocol handler (see Section 4.1, “Locating HTTP Artifacts”).
4.3.4. Configuring Pax URL Aether through settings.xml
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Overview
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You can optionally configure Pax URL Aether using a standard Maven
settings.xml file. This approach is particularly convenient in a development environment, because it makes it possible to store your build time settings and your run time settings all in one place.
Enabling the settings.xml configuration approach
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To configure Pax URL Aether to read its configuration from a Maven
settings.xml file, you must remove or comment out the org.ops4j.pax.url.mvn.repositories setting in the InstallDir/etc/org.ops4j.pax.url.mvn.cfg file. For example, you can comment out the default repositories setting by inserting a hash, #, at the start of the line, as follows:
#org.ops4j.pax.url.mvn.repositories= \
http://repo1.maven.org/maven2@id=maven.central.repo, \
https://maven.repository.redhat.com/ga@id=redhat.ga.repo, \
https://maven.repository.redhat.com/earlyaccess/all@id=redhat.ea.repo, \
https://repository.jboss.org/nexus/content/groups/ea@id=fuseearlyaccess
#org.ops4j.pax.url.mvn.repositories= \
http://repo1.maven.org/maven2@id=maven.central.repo, \
https://maven.repository.redhat.com/ga@id=redhat.ga.repo, \
https://maven.repository.redhat.com/earlyaccess/all@id=redhat.ea.repo, \
https://repository.jboss.org/nexus/content/groups/ea@id=fuseearlyaccess
When the repositories setting is absent, Pax URL Aether implicitly switches to the
settings.xml configuration approach.
Location of the settings.xml file
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By default, Pax URL Aether looks in the standard locations for the Maven
settings.xml file (usually UserHome/.m2/settings.xml). If you like, you can specify the location explicitly using the org.ops4j.pax.url.mvn.settings property. For example:
org.ops4j.pax.url.mvn.settings= /home/fuse/settings.xml
org.ops4j.pax.url.mvn.settings= /home/fuse/settings.xml
For full details of the search order for
settings.xml, see the description of org.ops4j.pax.url.mvn.settings in the section called “Pax URL Aether configuration reference”.
Adding a remote Maven repository
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To add a new remote Maven repository to your
settings.xml file, open the settings.xml file in a text editor and add a new repository XML element. For example, to create an entry for the JBoss Fuse public Maven repository, add a repository element as shown:
The preceding example additionally specifies that release artifacts can be downloaded, but snapshot artifacts cannot be downloaded from the repository.
Customizing the location of the local Maven repository
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To customize the location of your local Maven repository, open the
settings.xml file in a text editor and add (or modify) the localRepository XML element. For example, to select the directory, /home/fuse/.m2/repository, as your local Maven repository:
For a detailed explanation of the search order for the local Maven repository, see the section called “Local Maven repository search order”.
Configuring a HTTP proxy for Maven URLs
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To configure a HTTP proxy (which will be used when connecting to remote Maven repositories), open the
settings.xml file in a text editor and add a new proxy XML element as a child of the proxies XML element. The definition of the proxy follows the standard Maven syntax. For example, to create a proxy for the HTTP (insecure) protocol with host, 192.0.2.0, and port, 8080, add a proxy element as follows:
You can also add a proxy for secure HTTPS connections by adding a
proxy element configured with the https protocol.
Reference
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For a detailed description of the syntax of the Maven
settings.xml file, see the Maven Settings Reference. But please note that not all of the features documented there are necessarily supported by the Pax URL Aether component.
4.3.5. Pax URL Aether Reference
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Overview
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This section provides a configuration reference for the Pax URL Aether component, which is used to configure the runtime behaviour of Maven in the Karaf container.
Note
The prefix appearing in the property names,
org.ops4j.pax.url.mvn.*, reflects the old name of this component, which was previously called Pax URL Mvn.
Local Maven repository search order
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Pax URL Aether resolves the location of the local repository in the following order:
- The location specified by the
org.ops4j.pax.url.mvn.localRepositoryproperty in theorg.ops4j.pax.url.mvn.cfgfile. - Otherwise, the location specified by the
localRepositoryelement in thesettings.xmlfile specified by theorg.ops4j.pax.url.mvn.settingsproperty in theorg.ops4j.pax.url.mvn.cfgfile. - Otherwise, the location specified by the
localRepositoryelement in the.m2/settings.xmlfile located under the user's home directory. - Otherwise, the location specified by the
localRepositoryelement in theM2_HOME/conf/settings.xmlfile. - Otherwise, the default location is
.m2/repository/under the user's home directory.
Pax URL Aether Maven URL syntax
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The protocol handler registered by Pax URL Aether supports the following Maven URL syntax:
mvn:[RepositoryUrl!]GroupId/ArtifactId[/Version[/Type]]
mvn:[RepositoryUrl!]GroupId/ArtifactId[/Version[/Type]]
Where
RepositoryUrl has the syntax specified by the section called “Pax URL Aether repository URL syntax”; and GroupId, ArtifactId, Version, Type are the standard Maven location coordinates.
Pax URL Aether repository URL syntax
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You specify a repository location using a URL with a
file:, http:, or https: scheme, optionally appending one or more of the following suffixes:
@snapshots- Allow snapshot versions to be read from the repository.
@noreleases- Do not allow release versions to be read from the repository.
@id=RepoName- (Required) Specifies the repository name. This setting is required by the Aether handler.
@multi- Marks the path as a parent directory of multiple repository directories. At run time the parent directory is scanned for subdirectories and each subdirectory is used as a remote repository.
@update=UpdatePolicy- Specifies the Maven
updatePolicy, overriding the value oforg.ops4j.pax.url.mvn.globalUpdatePolicy. @releasesUpdate=UpdatePolicy- Specifies the Maven
updatePolicyspecifically for release artifacts (overriding the value of@update). @snapshotsUpdate=UpdatePolicy- Specifies the Maven
updatePolicyspecifically for snapshot artifacts (overriding the value of@update). @checksum=ChecksumPolicy- Specifies the Maven
checksumPolicy, which specifies how to react if a downloaded Maven artifact has a missing or incorrect checksum. The policy value can be:ignore,fail, orwarn. @releasesChecksum=ChecksumPolicy- Specifies the Maven
checksumPolicyspecifically for release artifacts (overriding the value of@checksum). @snapshotsChecksum=ChecksumPolicy- Specifies the Maven
checksumPolicyspecifically for snapshot artifacts (overriding the value of@checksum).
For example:
https://repo.example.org/maven/repository@id=example.repo
https://repo.example.org/maven/repository@id=example.repoPax URL Aether configuration reference
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The Pax URL Aether component can be configured by editing the
etc/org.ops4j.pax.url.mvn.cfg configuration file (uses OSGi Config Admin service). In pax-url-aether version 2.4.2, the following configuration properties are supported:
org.ops4j.pax.url.mvn.certificateCheck- If
true, enable the SSL certificate check when connecting to a remote repository through the HTTPS protocol. Iffalse, skip the SSL certificate check. Default isfalse. org.ops4j.pax.url.mvn.defaultRepositories- Specifies a list of default (local) Maven repositories that are checked before looking up the remote repositories. Specified as a comma-separated list of
file:repository URLs, where each repository URL has the syntax defined in the section called “Pax URL Aether repository URL syntax”. org.ops4j.pax.url.mvn.globalUpdatePolicy- Specifies the Maven
updatePolicy, which determines how often Aether attempts to update local Maven artifacts from remote repositories. Can take the following values:always—always resolve the latest SNAPSHOT from remote Maven repositories.never—never check for newer remote SNAPSHOTS.daily—check on the first run of the day (local time).interval:Mins—check everyMinsminutes.
Default isdaily. org.ops4j.pax.url.mvn.localRepository- Specifies the location of the local Maven repository on the file system, overriding the default value (which is usually
UserHome/.m2/repository). org.ops4j.pax.url.mvn.proxies- Can be used to specify a HTTP proxy, a HTTPS proxy, and non-proxy host lists. The value consists of a semicolon,
;, separated list of entries. You can include the following entries (where each entry is optional):http:host=Host,port=Port[,nonProxyHosts=NonProxyHosts]https:host=Host,port=Port[,nonProxyHosts=NonProxyHosts]
ThenonProxyHostssetting is optional and, if included, specifies a list of hosts that can be reached without going through the proxy. The list of non-proxy hosts has its entries separated by a pipe,|, symbol—for example,nonProxyHosts=localhost|example.org.Here is a sampleorg.ops4j.pax.url.mvn.proxiessetting:org.ops4j.pax.url.mvn.proxies= http:host=gateway,port=8080;https:host=sslgateway,port=8453
org.ops4j.pax.url.mvn.proxies= http:host=gateway,port=8080;https:host=sslgateway,port=8453Copy to Clipboard Copied! Toggle word wrap Toggle overflow org.ops4j.pax.url.mvn.proxySupport- If
true, enable HTTP proxy support through property settings. When this setting is enabled, the HTTP proxy can be configured in either of the following ways:- Through the
org.ops4j.pax.url.mvn.proxiesproperty (takes precedence), or - Through the
http.proxyHost,http.proxyPort, andhttp.nonProxyHostsJava system properties, set in theetc/system.propertiesfile.
Iffalse, the preceding property settings are ignored. Default istrue.NoteThis setting has no effect on proxy support when a Mavensettings.xmlfile is selected to configure Pax URL Aether. org.ops4j.pax.url.mvn.repositories- Specifies a list of remote Maven repositories that can be searched for Maven artifacts. Specified as a comma-separated list of
http:orhttps:repository URLs, where each repository URL has the syntax defined in the section called “Pax URL Aether repository URL syntax”.ImportantIf theorg.ops4j.pax.url.mvn.repositoriesproperty is not set, Pax URL Aether reads its Maven settings from the relevant Mavensettings.xmlfile instead (usually, fromUserHome/.m2/settings.xmlby default). In other words, the absence of theorg.ops4j.pax.url.mvn.repositoriesproperty implicitly enables thesettings.xmlconfiguration approach. org.ops4j.pax.url.mvn.security- Specifies the path to a Maven
settings-security.xmlfile. This can be used to enable server password encryption. Default is${user.home}/.m2/settings-security.xml. org.ops4j.pax.url.mvn.settings- Specifies a path on the file system to override the default location of the Maven
settings.xmlfile. Pax URL Aether resolves the location of the Mavensettings.xmlfile in the following order:- The location specified by
org.ops4j.pax.url.mvn.settings. ${user.home}/.m2/settings.xml${maven.home}/conf/settings.xmlM2_HOME/conf/settings.xml
NoteAllsettings.xmlfiles are ignored, if theorg.ops4j.pax.url.mvn.repositoriesproperty is set. org.ops4j.pax.url.mvn.timeout- Specifies the timeout to use while downloading artifacts, in units of milliseconds. Default is
5000(five seconds).
Part II. OSGi Bundle Deployment Model
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Abstract
The OSGi bundle is the underlying unit of deployment for the Red Hat JBoss Fuse container. You can either package and deploy your applications directly as bundles or use one of the alternative deployment models (WAR).
Chapter 5. Introduction to OSGi
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Abstract
The OSGi specification supports modular application development by defining a runtime framework that simplifies building, deploying, and managing complex applications.
5.1. Red Hat JBoss Fuse
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Overview
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Red Hat JBoss Fuse has the following layered architecture:
- Technology layer—includes technologies such as JAX-WS, JAX-RS, JMS, Spring, and JEE
- the section called “Red Hat JBoss Fuse” —a wrapper layer around the OSGi container implementation, which provides support for deploying the OSGi container as a runtime server. Runtime features provided by the JBoss Fuse include hot deployment, management, and administration features.
- OSGi framework —implements OSGi functionality, including managing dependencies and bundle lifecycles
Red Hat JBoss Fuse
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Figure 5.1 shows the architecture of JBoss Fuse.
Figure 5.1. Red Hat JBoss Fuse Architecture
JBoss Fuse is based on Apache Karaf, a powerful, lightweight, OSGi-based runtime container for deploying and managing bundles to facilitate componentization of applications. JBoss Fuse also provides native OS integration and can be integrated into the operating system as a service so that the lifecycle is bound to the operating system.
As shown in Figure 5.1, JBoss Fuse extends the OSGi layers with:
- Console— an extensible Gogo console manages services, installs and manages applications and libraries, and interacts with the JBoss Fuse runtime. It provides console commands to administer instances of JBoss Fuse. See the "Console Reference".
- Logging—a powerful, unified logging subsystem provides console commands to display, view and change log levels. See "Configuring and Running JBoss Fuse".
- Deployment—supports both manual deployment of OSGi bundles using the
osgi:installandosgi:startcommands and hot deployment of applications. When a JAR file, WAR file, or OSGi bundle is copied into the hot deployment folder InstallDir/deploy, it's automatically installed on-the-fly inside the Red Hat JBoss Fuse runtime. When you update or delete these files or bundles, the changes are made automatically (but only while the container is running!). See Section 7.1, “Hot Deployment”. - Provisioning—provides multiple mechanisms for installing applications and libraries. See Chapter 8, Deploying Features.
- Configuration—the properties files stored in the InstallDir
/etcfolder are continuously monitored, and changes to them are automatically propagated to the relevant services at configurable intervals. - Spring DM—simplifies building Spring applications that run in an OSGi framework. When a Spring configuration file is copied to the hot deployment folder, Red Hat JBoss Fuse generates an OSGi bundle on-the-fly and instantiates the Spring application context.
- Blueprint—is essentially a standardized version of Spring DM. It is a dependency injection framework that simplifies interaction with the OSGi container—for example, providing standard XML elements to import and export OSGi services. When a Blueprint configuration file is copied to the hot deployment folder, Red Hat JBoss Fuse generates an OSGi bundle on-the-fly and instantiates the Blueprint context.
5.2. OSGi Framework
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Overview
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The OSGi Alliance is an independent organization responsible for defining the features and capabilities of the OSGi Service Platform Release 4. The OSGi Service Platform is a set of open specifications that simplify building, deploying, and managing complex software applications.
OSGi technology is often referred to as the dynamic module system for Java. OSGi is a framework for Java that uses bundles to modularly deploy Java components and handle dependencies, versioning, classpath control, and class loading. OSGi's lifecycle management allows you to load, start, and stop bundles without shutting down the JVM.
OSGi provides the best runtime platform for Java, a superior class loading architecture, and a registry for services. Bundles can export services, run processes, and have their dependencies managed. Each bundle can have its requirements managed by the OSGi container.
JBoss Fuse uses Apache Felix as its default OSGi implementation. The framework layers form the container where you install bundles. The framework manages the installation and updating of bundles in a dynamic, scalable manner, and manages the dependencies between bundles and services.
OSGi architecture
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As shown in Figure 5.1, “Red Hat JBoss Fuse Architecture”, the OSGi framework contains the following:
- Bundles — Logical modules that make up an application. See Section 5.4, “OSGi Bundles”.
- Service layer — Provides communication among modules and their contained components. This layer is tightly integrated with the lifecycle layer. See Section 5.3, “OSGi Services”.
- Lifecycle layer — Provides access to the underlying OSGi framework. This layer handles the lifecycle of individual bundles so you can manage your application dynamically, including starting and stopping bundles.
- Module layer — Provides an API to manage bundle packaging, dependency resolution, and class loading.
- Execution environment — A configuration of a JVM. This environment uses profiles that define the environment in which bundles can work.
- Security layer — Optional layer based on Java 2 security, with additional constraints and enhancements.
Each layer in the framework depends on the layer beneath it. For example, the lifecycle layer requires the module layer. The module layer can be used without the lifecycle and service layers.
5.3. OSGi Services
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Overview
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An OSGi service is a Java class or service interface with service properties defined as name/value pairs. The service properties differentiate among service providers that provide services with the same service interface.
An OSGi service is defined semantically by its service interface, and it is implemented as a service object. A service's functionality is defined by the interfaces it implements. Thus, different applications can implement the same service.
Service interfaces allow bundles to interact by binding interfaces, not implementations. A service interface should be specified with as few implementation details as possible.
OSGi service registry
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In the OSGi framework, the service layer provides communication between bundles and their contained components using the publish, find, and bind service model. The service layer contains a service registry where:
- Service providers register services with the framework to be used by other bundles
- Service requesters find services and bind to service providers
Services are owned by, and run within, a bundle. The bundle registers an implementation of a service with the framework service registry under one or more Java interfaces. Thus, the service’s functionality is available to other bundles under the control of the framework, and other bundles can look up and use the service. Lookup is performed using the Java interface and service properties.
Each bundle can register multiple services in the service registry using the fully qualified name of its interface and its properties. Bundles use names and properties with LDAP syntax to query the service registry for services.
A bundle is responsible for runtime service dependency management activities including publication, discovery, and binding. Bundles can also adapt to changes resulting from the dynamic availability (arrival or departure) of the services that are bound to the bundle.
Event notification
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Service interfaces are implemented by objects created by a bundle. Bundles can:
- Register services
- Search for services
- Receive notifications when their registration state changes
The OSGi framework provides an event notification mechanism so service requesters can receive notification events when changes in the service registry occur. These changes include the publication or retrieval of a particular service and when services are registered, modified, or unregistered.
Service invocation model
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When a bundle wants to use a service, it looks up the service and invokes the Java object as a normal Java call. Therefore, invocations on services are synchronous and occur in the same thread. You can use callbacks for more asynchronous processing. Parameters are passed as Java object references. No marshalling or intermediary canonical formats are required as with XML. OSGi provides solutions for the problem of services being unavailable.
OSGi framework services
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In addition to your own services, the OSGi framework provides the following optional services to manage the operation of the framework:
- Package Admin service—allows a management agent to define the policy for managing Java package sharing by examining the status of the shared packages. It also allows the management agent to refresh packages and to stop and restart bundles as required. This service enables the management agent to make decisions regarding any shared packages when an exporting bundle is uninstalled or updated.The service also provides methods to refresh exported packages that were removed or updated since the last refresh, and to explicitly resolve specific bundles. This service can also trace dependencies between bundles at runtime, allowing you to see what bundles might be affected by upgrading.
- Start Level service—enables a management agent to control the starting and stopping order of bundles. The service assigns each bundle a start level. The management agent can modify the start level of bundles and set the active start level of the framework, which starts and stops the appropriate bundles. Only bundles that have a start level less than, or equal to, this active start level can be active.
- URL Handlers service—dynamically extends the Java runtime with URL schemes and content handlers enabling any component to provide additional URL handlers.
- Permission Admin service—enables the OSGi framework management agent to administer the permissions of a specific bundle and to provide defaults for all bundles. A bundle can have a single set of permissions that are used to verify that it is authorized to execute privileged code. You can dynamically manipulate permissions by changing policies on the fly and by adding new policies for newly installed components. Policy files are used to control what bundles can do.
- Conditional Permission Admin service—extends the Permission Admin service with permissions that can apply when certain conditions are either true or false at the time the permission is checked. These conditions determine the selection of the bundles to which the permissions apply. Permissions are activated immediately after they are set.
The OSGi framework services are described in detail in separate chapters in the OSGi Service Platform Release 4 specification available from the release 4 download page on the OSGi Alliance web site.
OSGi Compendium services
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In addition to the OSGi framework services, the OSGi Alliance defines a set of optional, standardized compendium services. The OSGi compendium services provide APIs for tasks such as logging and preferences. These services are described in the OSGi Service Platform, Service Compendium available from the release 4 download page on the OSGi Alliance Web site.
The Configuration Admin compendium service is like a central hub that persists configuration information and distributes it to interested parties. The Configuration Admin service specifies the configuration information for deployed bundles and ensures that the bundles receive that data when they are active. The configuration data for a bundle is a list of name-value pairs. See the section called “Red Hat JBoss Fuse”.
5.4. OSGi Bundles
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Overview
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With OSGi, you modularize applications into bundles. Each bundle is a tightly coupled, dynamically loadable collection of classes, JARs, and configuration files that explicitly declare any external dependencies. In OSGi, a bundle is the primary deployment format. Bundles are applications that are packaged in JARs, and can be installed, started, stopped, updated, and removed.
OSGi provides a dynamic, concise, and consistent programming model for developing bundles. Development and deployment are simplified by decoupling the service's specification (Java interface) from its implementation.
The OSGi bundle abstraction allows modules to share Java classes. This is a static form of reuse. The shared classes must be available when the dependent bundle is started.
A bundle is a JAR file with metadata in its OSGi manifest file. A bundle contains class files and, optionally, other resources and native libraries. You can explicitly declare which packages in the bundle are visible externally (exported packages) and which external packages a bundle requires (imported packages).
The module layer handles the packaging and sharing of Java packages between bundles and the hiding of packages from other bundles. The OSGi framework dynamically resolves dependencies among bundles. The framework performs bundle resolution to match imported and exported packages. It can also manage multiple versions of a deployed bundle.
Class Loading in OSGi
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OSGi uses a graph model for class loading rather than a tree model (as used by the JVM). Bundles can share and re-use classes in a standardized way, with no runtime class-loading conflicts.
Each bundle has its own internal classpath so that it can serve as an independent unit if required.
The benefits of class loading in OSGi include:
- Sharing classes directly between bundles. There is no requirement to promote JARs to a parent class-loader.
- You can deploy different versions of the same class at the same time, with no conflict.
Chapter 6. Building an OSGi Bundle
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Abstract
This chapter describes how to build an OSGi bundle using Maven. For building bundles, the Maven bundle plug-in plays a key role, because it enables you to automate the generation of OSGi bundle headers (which would otherwise be a tedious task). Maven archetypes, which generate a complete sample project, can also provide a starting point for your bundle projects.
6.1. Generating a Bundle Project
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Generating bundle projects with Maven archetypes
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To help you get started quickly, you can invoke a Maven archetype to generate the initial outline of a Maven project (a Maven archetype is analogous to a project wizard). The following Maven archetypes can generate projects for building OSGi bundles:
Apache CXF karaf-soap-archetype archetype
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The Apache CXF karaf-soap-archetype archetype creates a project for building a service from Java. To generate a Maven project with the coordinates, GroupId
:ArtifactId:Version, enter the following command:
Note
The backslash character,
\, indicates line continuation on Linux and UNIX operating systems. On Windows platforms, you must omit the backslash character and put all of the arguments on a single line.
Apache Camel archetype
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The Apache Camel OSGi archetype creates a project for building a route that can be deployed into the OSGi container. To generate a Maven project with the coordinates, GroupId
:ArtifactId:Version, enter the following command:
Building the bundle
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By default, the preceding archetypes create a project in a new directory, whose names is the same as the specified artifact ID, ArtifactId. To build the bundle defined by the new project, open a command prompt, go to the project directory (that is, the directory containing the
pom.xml file), and enter the following Maven command:
mvn install
mvn install
The effect of this command is to compile all of the Java source files, to generate a bundle JAR under the ArtifactId
/target directory, and then to install the generated JAR in the local Maven repository.
6.2. Modifying an Existing Maven Project
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Overview
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If you already have a Maven project and you want to modify it so that it generates an OSGi bundle, perform the following steps:
Change the package type to bundle
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Configure Maven to generate an OSGi bundle by changing the package type to
bundle in your project's pom.xml file. Change the contents of the packaging element to bundle, as shown in the following example:
<project ... > ... <packaging>bundle</packaging> ... </project>
<project ... >
...
<packaging>bundle</packaging>
...
</project>
The effect of this setting is to select the Maven bundle plug-in,
maven-bundle-plugin, to perform packaging for this project. This setting on its own, however, has no effect until you explicitly add the bundle plug-in to your POM.
Add the bundle plug-in to your POM
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To add the Maven bundle plug-in, copy and paste the following sample
plugin element into the project/build/plugins section of your project's pom.xml file:
Where the bundle plug-in is configured by the settings in the
instructions element.
Customize the bundle plug-in
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For some specific recommendations on configuring the bundle plug-in for Apache CXF, see Section 6.3, “Packaging a Web Service in a Bundle”.
For an in-depth discussion of bundle plug-in configuration, in the context of the OSGi framework and versioning policy, see "Managing OSGi Dependencies".
Customize the JDK compiler version
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It is almost always necessary to specify the JDK version in your POM file. If your code uses any modern features of the Java language—such as generics, static imports, and so on—and you have not customized the JDK version in the POM, Maven will fail to compile your source code. It is not sufficient to set the
JAVA_HOME and the PATH environment variables to the correct values for your JDK, you must also modify the POM file.
To configure your POM file, so that it accepts the Java language features introduced in JDK 1.7, add the following
maven-compiler-plugin plug-in settings to your POM (if they are not already present):
6.3. Packaging a Web Service in a Bundle
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Overview
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This section explains how to modify an existing Maven project for a Apache CXF application, so that the project generates an OSGi bundle suitable for deployment in the Red Hat JBoss Fuse OSGi container. To convert the Maven project, you need to modify the project's POM file and the project's Spring XML file(s) (located in
META-INF/spring).
Modifying the POM file to generate a bundle
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To configure a Maven POM file to generate a bundle, there are essentially two changes you need to make: change the POM's package type to
bundle; and add the Maven bundle plug-in to your POM. For details, see Section 6.1, “Generating a Bundle Project”.
Mandatory import packages
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In order for your application to use the Apache CXF components, you need to import their packages into the application's bundle. Because of the complex nature of the dependencies in Apache CXF, you cannot rely on the Maven bundle plug-in, or the bnd tool, to automatically determine the needed imports. You will need to explicitly declare them.
You need to import the following packages into your bundle:
Sample Maven bundle plug-in instructions
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Example 6.1, “Configuration of Mandatory Import Packages” shows how to configure the Maven bundle plug-in in your POM to import the mandatory packages. The mandatory import packages appear as a comma-separated list inside the
Import-Package element. Note the appearance of the wildcard, *, as the last element of the list. The wildcard ensures that the Java source files from the current bundle are scanned to discover what additional packages need to be imported.
Example 6.1. Configuration of Mandatory Import Packages
Add a code generation plug-in
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A Web services project typically requires code to be generated. Apache CXF provides two Maven plug-ins for the JAX-WS front-end, which enable tyou to integrate the code generation step into your build. The choice of plug-in depends on whether you develop your service using the Java-first approach or the WSDL-first approach, as follows:
- Java-first approach—use the
cxf-java2ws-pluginplug-in. - WSDL-first approach—use the
cxf-codegen-pluginplug-in.
OSGi configuration properties
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The OSGi Configuration Admin service defines a mechanism for passing configuration settings to an OSGi bundle. You do not have to use this service for configuration, but it is typically the most convenient way of configuring bundle applications. Both Spring DM and Blueprint provide support for OSGi configuration, enabling you to substitute variables in a Spring XML file or a Blueprint file using values obtained from the OSGi Configuration Admin service.
For details of how to use OSGi configuration properties, see Section 6.4, “Configuring the Bundle Plug-In” and the section called “Add OSGi configurations to the feature”.
6.4. Configuring the Bundle Plug-In
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Overview
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A bundle plug-in requires very little information to function. All of the required properties use default settings to generate a valid OSGi bundle.
While you can create a valid bundle using just the default values, you will probably want to modify some of the values. You can specify most of the properties inside the plug-in's
instructions element.
Configuration properties
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Some of the commonly used configuration properties are:
Setting a bundle's symbolic name
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By default, the bundle plug-in sets the value for the Bundle-SymbolicName property to groupId
+ "." + artifactId, with the following exceptions:
- If groupId has only one section (no dots), the first package name with classes is returned.For example, if the group Id is
commons-logging:commons-logging, the bundle's symbolic name isorg.apache.commons.logging. - If artifactId is equal to the last section of groupId, then groupId is used.For example, if the POM specifies the group ID and artifact ID as
org.apache.maven:maven, the bundle's symbolic name isorg.apache.maven. - If artifactId starts with the last section of groupId, that portion is removed.For example, if the POM specifies the group ID and artifact ID as
org.apache.maven:maven-core, the bundle's symbolic name isorg.apache.maven.core.
To specify your own value for the bundle's symbolic name, add a
Bundle-SymbolicName child in the plug-in's instructions element, as shown in Example 6.2.
Example 6.2. Setting a bundle's symbolic name
Setting a bundle's name
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By default, a bundle's name is set to
${project.name}.
To specify your own value for the bundle's name, add a
Bundle-Name child to the plug-in's instructions element, as shown in Example 6.3.
Example 6.3. Setting a bundle's name
Setting a bundle's version
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By default, a bundle's version is set to
${project.version}. Any dashes (-) are replaced with dots (.) and the number is padded up to four digits. For example, 4.2-SNAPSHOT becomes 4.2.0.SNAPSHOT.
To specify your own value for the bundle's version, add a
Bundle-Version child to the plug-in's instructions element, as shown in Example 6.4.
Example 6.4. Setting a bundle's version
Specifying exported packages
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By default, the OSGi manifest's
Export-Package list is populated by all of the packages in your local Java source code (under src/main/java), except for the deault package, ., and any packages containing .impl or .internal.
Important
If you use a
Private-Package element in your plug-in configuration and you do not specify a list of packages to export, the default behavior includes only the packages listed in the Private-Package element in the bundle. No packages are exported.
The default behavior can result in very large packages and in exporting packages that should be kept private. To change the list of exported packages you can add an
Export-Package child to the plug-in's instructions element.
The
Export-Package element specifies a list of packages that are to be included in the bundle and that are to be exported. The package names can be specified using the * wildcard symbol. For example, the entry com.fuse.demo.* includes all packages on the project's classpath that start with com.fuse.demo.
You can specify packages to be excluded be prefixing the entry with
!. For example, the entry !com.fuse.demo.private excludes the package com.fuse.demo.private.
When excluding packages, the order of entries in the list is important. The list is processed in order from the beginning and any subsequent contradicting entries are ignored.
For example, to include all packages starting with com.fuse.demo except the package com.fuse.demo.private, list the packages using:
!com.fuse.demo.private,com.fuse.demo.*
!com.fuse.demo.private,com.fuse.demo.*
However, if you list the packages using com.fuse.demo.*,!com.fuse.demo.private, then com.fuse.demo.private is included in the bundle because it matches the first pattern.
Specifying private packages
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If you want to specify a list of packages to include in a bundle without exporting them, you can add a
Private-Package instruction to the bundle plug-in configuration. By default, if you do not specify a Private-Package instruction, all packages in your local Java source are included in the bundle.
Important
If a package matches an entry in both the
Private-Package element and the Export-Package element, the Export-Package element takes precedence. The package is added to the bundle and exported.
The
Private-Package element works similarly to the Export-Package element in that you specify a list of packages to be included in the bundle. The bundle plug-in uses the list to find all classes on the project's classpath that are to be included in the bundle. These packages are packaged in the bundle, but not exported (unless they are also selected by the Export-Package instruction).
Example 6.5 shows the configuration for including a private package in a bundle
Example 6.5. Including a private package in a bundle
Specifying imported packages
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By default, the bundle plug-in populates the OSGi manifest's
Import-Package property with a list of all the packages referred to by the contents of the bundle.
While the default behavior is typically sufficient for most projects, you might find instances where you want to import packages that are not automatically added to the list. The default behavior can also result in unwanted packages being imported.
To specify a list of packages to be imported by the bundle, add an
Import-Package child to the plug-in's instructions element. The syntax for the package list is the same as for the Export-Package element and the Private-Package element.
Important
When you use the
Import-Package element, the plug-in does not automatically scan the bundle's contents to determine if there are any required imports. To ensure that the contents of the bundle are scanned, you must place an * as the last entry in the package list.
Example 6.6 shows the configuration for specifying the packages imported by a bundle
Example 6.6. Specifying the packages imported by a bundle
More information
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For more information on configuring a bundle plug-in, see:
Chapter 7. Deploying an OSGi Bundle
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Abstract
Apache Karaf provides two different approaches for deploying a single OSGi bundle: hot deployment or manual deployment. If you need to deploy a collection of related bundles, on the other hand, it is recommended that you deploy them together as a feature, rather than singly (see Chapter 8, Deploying Features).
7.1. Hot Deployment
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Hot deploy directory
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JBoss Fuse monitors JAR files in the
InstallDir/deploy directory and hot deploys everything in this directory. Each time a JAR file is copied to this directory, it is installed in the runtime and also started. You can subsequently update or delete the JARs, and the changes are handled automatically.
For example, if you have just built the bundle, ProjectDir
/target/foo-1.0-SNAPSHOT.jar, you can deploy this bundle by copying it to the InstallDir/deploy directory as follows (assuming you are working on a UNIX platform):
% cp ProjectDir/target/foo-1.0-SNAPSHOT.jar InstallDir/deploy
% cp ProjectDir/target/foo-1.0-SNAPSHOT.jar InstallDir/deployHot undeploying a bundle
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To undeploy a bundle from the hot deploy directory, simply delete the bundle file from the
InstallDir/deploy directory while the Apache Karaf container is running.
Important
The hot undeploy mechanism does not work while the container is shut down. If you shut down the Karaf container, delete the bundle file from
deploy/, and then restart the Karaf container, the bundle will not be undeployed after you restart the container (you can, however, undeploy the bundle manually using the osgi:uninstall console command).
7.2. Manual Deployment
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Overview
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You can manually deploy and undeploy bundles by issuing commands at the Red Hat JBoss Fuse console.
Installing a bundle
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Use the
osgi:install command to install one or more bundles in the OSGi container. This command has the following syntax:
osgi:install [-s] [--start] [--help] UrlList
osgi:install [-s] [--start] [--help] UrlList
Where UrlList is a whitespace-separated list of URLs that specify the location of each bundle to deploy. The following command arguments are supported:
-s- Start the bundle after installing.
--start- Same as
-s. --help- Show and explain the command syntax.
For example, to install and start the bundle, ProjectDir
/target/foo-1.0-SNAPSHOT.jar, enter the following command at the Karaf console prompt:
osgi:install -s file:ProjectDir/target/foo-1.0-SNAPSHOT.jar
osgi:install -s file:ProjectDir/target/foo-1.0-SNAPSHOT.jarNote
On Windows platforms, you must be careful to use the correct syntax for the
file URL in this command. See Section A.1, “File URL Handler” for details.
Uninstalling a bundle
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To uninstall a bundle, you must first obtain its bundle ID using the
osgi:list command. You can then uninstall the bundle using the osgi:uninstall command (which takes the bundle ID as its argument).
For example, if you have already installed the bundle named
A Camel OSGi Service Unit, entering osgi:list at the console prompt might produce output like the following:
... [ 181] [Resolved ] [ ] [ ] [ 60] A Camel OSGi Service Unit (1.0.0.SNAPSHOT)
...
[ 181] [Resolved ] [ ] [ ] [ 60] A Camel OSGi Service Unit (1.0.0.SNAPSHOT)
You can now uninstall the bundle with the ID,
181, by entering the following console command:
osgi:uninstall 181
osgi:uninstall 181URL schemes for locating bundles
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When specifying the location URL to the
osgi:install command, you can use any of the URL schemes supported by Red Hat JBoss Fuse, which includes the following scheme types:
Redeploying bundles automatically using dev:watch
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In a development environment—where a developer is constantly changing and rebuilding a bundle—it is typically necessary to re-install the bundle multiple times. Using the
dev:watch command, you can instruct Karaf to monitor your local Maven repository and re-install a particular bundle automatically, as soon as it changes in your local Maven repository.
For example, given a particular bundle—with bundle ID,
751—you can enable automatic redeployment by entering the command:
dev:watch 751
dev:watch 751
Now, whenever you rebuild and install the Maven artifact into your local Maven repository (for example, by executing
mvn install in your Maven project), the Karaf container automatically re-installs the changed Maven artifact. For more details, see section "dev:watch, watch" in "Console Reference".
Important
Using the
dev:watch command is intended for a development environment only. It is not recommended for use in a production environment.
7.3. Lifecycle Management
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Bundle lifecycle states
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Applications in an OSGi environment are subject to the lifecycle of its bundles. Bundles have six lifecycle states:
- Installed — All bundles start in the installed state. Bundles in the installed state are waiting for all of their dependencies to be resolved, and once they are resolved, bundles move to the resolved state.
- Resolved — Bundles are moved to the resolved state when the following conditions are met:
- The runtime environment meets or exceeds the environment specified by the bundle.
- All of the packages imported by the bundle are exposed by bundles that are either in the resolved state or that can be moved into the resolved state at the same time as the current bundle.
- All of the required bundles are either in the resolved state or they can be resolved at the same time as the current bundle.
ImportantAll of an application's bundles must be in the resolved state before the application can be started.If any of the above conditions ceases to be satisfied, the bundle is moved back into the installed state. For example, this can happen when a bundle that contains an imported package is removed from the container. - Starting — The starting state is a transitory state between the resolved state and the active state. When a bundle is started, the container must create the resources for the bundle. The container also calls the
start()method of the bundle's bundle activator when one is provided. - Active — Bundles in the active state are available to do work. What a bundle does in the active state depends on the contents of the bundle. For example, a bundle containing a JAX-WS service provider indicates that the service is available to accept requests.
- Stopping — The stopping state is a transitory state between the active state and the resolved state. When a bundle is stopped, the container must clean up the resources for the bundle. The container also calls the
stop()method of the bundle's bundle activator when one is provided. - Uninstalled — When a bundle is uninstalled it is moved from the resolved state to the uninstalled state. A bundle in this state cannot be transitioned back into the resolved state or any other state. It must be explicitly re-installed.
The most important lifecycle states for application developers are the starting state and the stopping state. The endpoints exposed by an application are published during the starting state. The published endpoints are stopped during the stopping state.
Installing and resolving bundles
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When you install a bundle using the
osgi:install command (without the -s flag), the kernel installs the specified bundle and attempts to put it into the resolved state. If the resolution of the bundle fails for some reason (for example, if one of its dependencies is unsatisfied), the kernel leaves the bundle in the installed state.
At a later time (for example, after you have installed missing dependencies) you can attempt to move the bundle into the resolved state by invoking the
osgi:resolve command, as follows:
osgi:resolve 181
osgi:resolve 181
Where the argument (
181, in this example) is the ID of the bundle you want to resolve.
Starting and stopping bundles
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You can start one or more bundles (from either the installed or the resolved state) using the
osgi:start command. For example, to start the bundles with IDs, 181, 185, and 186, enter the following console command:
osgi:start 181 185 186
osgi:start 181 185 186
You can stop one or more bundles using the
osgi:stop command. For example, to stop the bundles with IDs, 181, 185, and 186, enter the following console command:
osgi:stop 181 185 186
osgi:stop 181 185 186
You can restart one or more bundles (that is, moving from the started state to the resolved state, and then back again to the started state) using the
osgi:restart command. For example, to restart the bundles with IDs, 181, 185, and 186, enter the following console command:
osgi:restart 181 185 186
osgi:restart 181 185 186Bundle start level
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A start level is associated with every bundle. The start level is a positive integer value that controls the order in which bundles are activated/started. Bundles with a low start level are started before bundles with a high start level. Hence, bundles with the start level,
1, are started first and bundles belonging to the kernel tend to have lower start levels, because they provide the prerequisites for running most other bundles.
Typically, the start level of user bundles is 60 or higher.
Specifying a bundle's start level
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Use the
osgi:bundle-level command to set the start level of a particular bundle. For example, to configure the bundle with ID, 181, to have a start level of 70, enter the following console command:
osgi:bundle-level 181 70
osgi:bundle-level 181 70System start level
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The OSGi container itself has a start level associated with it and this system start level determines which bundles can be active and which cannot: only those bundles whose start level is less than or equal to the system start level can be active.
To discover the current system start level, enter
osgi:start-level in the console, as follows:
JBossFuse:karaf@root> osgi:start-level Level 100
JBossFuse:karaf@root> osgi:start-level
Level 100
If you want to change the system start level, provide the new start level as an argument to the
osgi:start-level command, as follows:
osgi:start-level 200
osgi:start-level 2007.4. Troubleshooting Dependencies
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Missing dependencies
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The most common issue that can arise when you deploy an OSGi bundle into the Red Hat JBoss Fuse container is that one or more dependencies are missing. This problem shows itself when you try to resolve the bundle in the OSGi container, usually as a side effect of starting the bundle. The bundle fails to resolve (or start) and a
ClassNotFound error is logged (to view the log, use the log:display console command or look at the log file in the InstallDir/data/log directory).
There are two basic causes of a missing dependency: either a required feature or bundle is not installed in the container; or your bundle's
Import-Package header is incomplete.
Required features or bundles are not installed
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Evidently, all features and bundles required by your bundle must already be installed in the OSGi container, before you attempt to resolve your bundle. In particular, because Apache Camel has a modular architecture, where each component is installed as a separate feature, it is easy to forget to install one of the required components.
Note
Consider packaging your bundle as a feature. Using a feature, you can package your bundle together with all of its dependencies and thus ensure that they are all installed simultaneously. For details, see Chapter 8, Deploying Features.
Import-Package header is incomplete
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If all of the required features and bundles are already installed and you are still getting a
ClassNotFound error, this means that the Import-Package header in your bundle's MANIFEST.MF file is incomplete. The maven-bundle-plugin (see Section 6.2, “Modifying an Existing Maven Project”) is a great help when it comes to generating your bundle's Import-Package header, but you should note the following points:
- Make sure that you include the wildcard,
*, in theImport-Packageelement of the Maven bundle plug-in configuration. The wildcard directs the plug-in to scan your Java source code and automatically generates a list of package dependencies. - The Maven bundle plug-in is not able to figure out dynamic dependencies. For example, if your Java code explicitly calls a class loader to load a class dynamically, the bundle plug-in does not take this into account and the required Java package will not be listed in the generated
Import-Packageheader. - If you define a Spring XML file (for example, in the
META-INF/springdirectory), the Maven bundle plug-in is not able to figure out dependencies arising from the Spring XML configuration. Any dependencies arising from Spring XML must be added manually to the bundle plug-in'sImport-Packageelement. - If you define a blueprint XML file (for example, in the
OSGI-INF/blueprintdirectory), any dependencies arising from the blueprint XML file are automatically resolved at run time. This is an important advantage of blueprint over Spring.
How to track down missing dependencies
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To track down missing dependencies, perform the following steps:
- Perform a quick check to ensure that all of the required bundles and features are actually installed in the OSGi container. You can use
osgi:listto check which bundles are installed andfeatures:listto check which features are installed. - Install (but do not start) your bundle, using the
osgi:installconsole command. For example:JBossFuse:karaf@root> osgi:install MyBundleURL
JBossFuse:karaf@root> osgi:install MyBundleURLCopy to Clipboard Copied! Toggle word wrap Toggle overflow - Use the
dev:dynamic-importconsole command to enable dynamic imports on the bundle you just installed. For example, if the bundle ID of your bundle is 218, you would enable dynamic imports on this bundle by entering the following command:JBossFuse:karaf@root> dev:dynamic-import 218
JBossFuse:karaf@root> dev:dynamic-import 218Copy to Clipboard Copied! Toggle word wrap Toggle overflow This setting allows OSGi to resolve dependencies using any of the bundles already installed in the container, effectively bypassing the usual dependency resolution mechanism (based on theImport-Packageheader). This is not recommemded for normal deployment, because it bypasses version checks: you could easily pick up the wrong version of a package, causing your application to malfunction. - You should now be able to resolve your bundle. For example, if your bundle ID is 218, enter the followng console command:
JBossFuse:karaf@root> osgi:resolve 218
JBossFuse:karaf@root> osgi:resolve 218Copy to Clipboard Copied! Toggle word wrap Toggle overflow - Assuming your bundle is now resolved (check the bundle status using
osgi:list), you can get a complete list of all the packages wired to your bundle using thepackage:importscommand. For example, if your bundle ID is 218, enter the following console command:JBossFuse:karaf@root> package:imports 218
JBossFuse:karaf@root> package:imports 218Copy to Clipboard Copied! Toggle word wrap Toggle overflow You should see a list of dependent packages in the console window (where the package names are highlighted in this example):Spring Beans (67): org.springframework.beans.factory.xml; version=3.0.5.RELEASE Web Services Metadata 2.0 (104): javax.jws; version=2.0.0 Apache CXF Bundle Jar (125): org.apache.cxf.helpers; version=2.4.2.fuse-00-08 Apache CXF Bundle Jar (125): org.apache.cxf.transport.jms.wsdl11; version=2.4.2.fuse-00-08 ...
Spring Beans (67): org.springframework.beans.factory.xml; version=3.0.5.RELEASE Web Services Metadata 2.0 (104): javax.jws; version=2.0.0 Apache CXF Bundle Jar (125): org.apache.cxf.helpers; version=2.4.2.fuse-00-08 Apache CXF Bundle Jar (125): org.apache.cxf.transport.jms.wsdl11; version=2.4.2.fuse-00-08 ...Copy to Clipboard Copied! Toggle word wrap Toggle overflow - Unpack your bundle JAR file and look at the packages listed under the
Import-Packageheader in theMETA-INF/MANIFEST.MFfile. Compare this list with the list of packages found in the previous step. Now, compile a list of the packages that are missing from the manifest'sImport-Packageheader and add these package names to theImport-Packageelement of the Maven bundle plug-in configuration in your project's POM file. - To cancel the dynamic import option, you must uninstall the old bundle from the OSGi container. For example, if your bundle ID is 218, enter the following command:
JBossFuse:karaf@root> osgi:uninstall 218
JBossFuse:karaf@root> osgi:uninstall 218Copy to Clipboard Copied! Toggle word wrap Toggle overflow - You can now rebuild your bundle with the updated list of imported packages and test it in the OSGi container.
Chapter 8. Deploying Features
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Abstract
Because applications and other tools typically consist of multiple OSGi bundles, it is often convenient to aggregate inter-dependent or related bundles into a larger unit of deployment. Red Hat JBoss Fuse therefore provides a scalable unit of deployment, the feature, which enables you to deploy multiple bundles (and, optionally, dependencies on other features) in a single step.
8.1. Creating a Feature
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Overview
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Essentially, a feature is created by adding a new
feature element to a special kind of XML file, known as a feature repository. To create a feature, perform the following steps:
Create a custom feature repository
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If you have not already defined a custom feature repository, you can create one as follows. Choose a convenient location for the feature repository on your file system—for example,
C:\Projects\features.xml—and use your favorite text editor to add the following lines to it:
<?xml version="1.0" encoding="UTF-8"?> <features name="CustomRepository"> </features>
<?xml version="1.0" encoding="UTF-8"?>
<features name="CustomRepository">
</features>
Where you must specify a name for the repository, CustomRepository, by setting the
name attribute.
Note
In contrast to a Maven repository or an OBR, a feature repository does not provide a storage location for bundles. A feature repository merely stores an aggregate of references to bundles. The bundles themselves are stored elsewhere (for example, in the file system or in a Maven repository).
Add a feature to the custom feature repository
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To add a feature to the custom feature repository, insert a new
feature element as a child of the root features element. You must give the feature a name and you can list any number of bundles belonging to the feature, by inserting bundle child elements. For example, to add a feature named example-camel-bundle containing the single bundle, C:\Projects\camel-bundle\target\camel-bundle-1.0-SNAPSHOT.jar, add a feature element as follows:
The contents of the
bundle element can be any valid URL, giving the location of a bundle (see Appendix A, URL Handlers). You can optionally specify a version attribute on the feature element, to assign a non-zero version to the feature (you can then specify the version as an optional argument to the features:install command).
To check whether the features service successfully parses the new feature entry, enter the following pair of console commands:
JBossFuse:karaf@root> features:refreshUrl JBossFuse:karaf@root> features:list ... [uninstalled] [0.0.0 ] example-camel-bundle MyFeaturesRepo ...
JBossFuse:karaf@root> features:refreshUrl
JBossFuse:karaf@root> features:list
...
[uninstalled] [0.0.0 ] example-camel-bundle MyFeaturesRepo
...
The
features:list command typically produces a rather long listing of features, but you should be able to find the entry for your new feature (in this case, example-camel-bundle) by scrolling back through the listing. The features:refreshUrl command forces the kernel to reread all the feature repositories: if you did not issue this command, the kernel would not be aware of any recent changes that you made to any of the repositories (in particular, the new feature would not appear in the listing).
To avoid scrolling through the long list of features, you can
grep for the example-camel-bundle feature as follows:
JBossFuse:karaf@root> features:list | grep example-camel-bundle [uninstalled] [0.0.0 ] example-camel-bundle MyFeaturesRepo
JBossFuse:karaf@root> features:list | grep example-camel-bundle
[uninstalled] [0.0.0 ] example-camel-bundle MyFeaturesRepo
Where the
grep command (a standard UNIX pattern matching utility) is built into the shell, so this command also works on Windows platforms.
Add the local repository URL to the features service
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In order to make the new feature repository available to Apache Karaf, you must add the feature repository using the
features:addUrl console command. For example, to make the contents of the repository, C:\Projects\features.xml, available to the kernel, you would enter the following console command:
features:addUrl file:C:/Projects/features.xml
features:addUrl file:C:/Projects/features.xml
Where the argument to
features:addUrl can be specified using any of the supported URL formats (see Appendix A, URL Handlers).
You can check that the repository's URL is registered correctly by entering the
features:listUrl console command, to get a complete listing of all registered feature repository URLs, as follows:
JBossFuse:karaf@root> features:listUrl file:C:/Projects/features.xml mvn:org.apache.ode/ode-jbi-karaf/1.3.3-fuse-01-00/xml/features mvn:org.apache.felix.karaf/apache-felix-karaf/1.2.0-fuse-01-00/xml/features
JBossFuse:karaf@root> features:listUrl
file:C:/Projects/features.xml
mvn:org.apache.ode/ode-jbi-karaf/1.3.3-fuse-01-00/xml/features
mvn:org.apache.felix.karaf/apache-felix-karaf/1.2.0-fuse-01-00/xml/featuresAdd dependent features to the feature
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If your feature depends on other features, you can specify these dependencies by adding
feature elements as children of the original feature element. Each child feature element contains the name of a feature on which the current feature depends. When you deploy a feature with dependent features, the dependency mechanism checks whether or not the dependent features are installed in the container. If not, the dependency mechanism automatically installs the missing dependencies (and any recursive dependencies).
For example, for the custom Apache Camel feature,
example-camel-bundle, you can specify explicitly which standard Apache Camel features it depends on. This has the advantage that the application could now be successfully deployed and run, even if the OSGi container does not have the required features pre-deployed. For example, you can define the example-camel-bundle feature with Apache Camel dependencies as follows:
Specifying the
version attribute is optional. When present, it enables you to select the specified version of the feature.
Add OSGi configurations to the feature
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If your application uses the OSGi Configuration Admin service, you can specify configuration settings for this service using the
config child element of your feature definition. For example, to specify that the prefix property has the value, MyTransform, add the following config child element to your feature's configuration:
Where the
name attribute of the config element specifies the persistent ID of the property settings (where the persistent ID acts effectively as a name scope for the property names). The content of the config element is parsed in the same way as a Java properties file.
The settings in the
config element can optionally be overridden by the settings in the Java properties file located in the InstallDir/etc directory, which is named after the persistent ID, as follows:
InstallDir/etc/org.fusesource.fuseesb.example.cfg
InstallDir/etc/org.fusesource.fuseesb.example.cfg
As an example of how the preceding configuration properties can be used in practice, consider the following Blueprint XML file that accesses the OSGi configuration properties:
When this Blueprint XML file is deployed in the
example-camel-bundle bundle, the property reference, ${prefix}, is replaced by the value, MyTransform, which is specified by the config element in the feature repository.
Automatically deploy an OSGi configuration
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By adding a
configfile element to a feature, you can ensure that an OSGi configuration file gets added to the InstallDir/etc directory at the same time that the feature is installed. This means that you can conveniently install a feature and its associated configuration at the same time.
For example, given that the
org.fusesource.fuseesb.example.cfg configuration file is archived in a Maven repository at mvn:org.fusesource.fuseesb.example/configadmin/1.0/cfg, you could deploy the configuration file by adding the following element to the feature:
<configfile finalname="etc/org.fusesource.fuseesb.example.cfg"> mvn:org.fusesource.fuseesb.example/configadmin/1.0/cfg </configfile>
<configfile finalname="etc/org.fusesource.fuseesb.example.cfg">
mvn:org.fusesource.fuseesb.example/configadmin/1.0/cfg
</configfile>8.2. Deploying a Feature
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Overview
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You can deploy a feature in one of the following ways:
- Install at the console, using
features:install. - Use hot deployment.
- Modify the boot configuration (first boot only!).
Installing at the console
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After you have created a feature (by adding an entry for it in a feature repository and registering the feature repository), it is relatively easy to deploy the feature using the
features:install console command. For example, to deploy the example-camel-bundle feature, enter the following pair of console commands:
JBossFuse:karaf@root> features:refreshUrl JBossFuse:karaf@root> features:install example-camel-bundle
JBossFuse:karaf@root> features:refreshUrl
JBossFuse:karaf@root> features:install example-camel-bundle
It is recommended that you invoke the
features:refreshUrl command before calling features:install, in case any recent changes were made to the features in the feature repository which the kernel has not picked up yet. The features:install command takes the feature name as its argument (and, optionally, the feature version as its second argument).
Note
Features use a flat namespace. So when naming your features, be careful to avoid name clashes with existing features.
Uninstalling at the console
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To uninstall a feature, invoke the
features:uninstall command as follows:
JBossFuse:karaf@root> features:uninstall example-camel-bundle
JBossFuse:karaf@root> features:uninstall example-camel-bundleNote
After uninstalling, the feature will still be visible when you invoke
features:list, but its status will now be flagged as [uninstalled].
Hot deployment
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You can hot deploy all of the features in a feature repository simply by copying the feature repository file into the
InstallDir/deploy directory.
As it is unlikely that you would want to hot deploy an entire feature repository at once, it is often more convenient to define a reduced feature repository or feature descriptor, which references only those features you want to deploy. The feature descriptor has exactly the same syntax as a feature repository, but it is written in a different style. The difference is that a feature descriptor consists only of references to existing features from a feature repository.
For example, you could define a feature descriptor to load the
example-camel-bundle feature as follows:
The repository element specifies the location of the custom feature repository, RepositoryURL (where you can use any of the URL formats described in Appendix A, URL Handlers). The feature,
hot-example-camel-bundle, is just a reference to the existing feature, example-camel-bundle.
Hot undeploying a features file
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To undeploy a features file from the hot deploy directory, simply delete the features file from the
InstallDir/deploy directory while the Apache Karaf container is running.
Important
The hot undeploy mechanism does not work while the container is shut down. If you shut down the Karaf container, delete the features file from
deploy/, and then restart the Karaf container, the features will not be undeployed after you restart the container (you can, however, undeploy the features manually using the features:uninstall console command).
Adding a feature to the boot configuration
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If you want to provision copies of Apache Karaf for deployment on multiple hosts, you might be interested in adding a feature to the boot configuration, which determines the collection of features that are installed when Apache Karaf boots up for the very first time.
The configuration file,
/etc/org.apache.karaf.features.cfg, in your install directory contains the following settings:
This configuration file has two properties:
featuresRepositories—comma separated list of feature repositories to load at startup.featuresBoot—comma separated list of features to install at startup.featuresBlackList—comma separated list of features that are prevented from being installed (to protect against unsupported or buggy features).
You can modify the configuration to customize the features that are installed as JBoss Fuse starts up. You can also modify this configuration file, if you plan to distribute JBoss Fuse with pre-installed features.
Important
This method of adding a feature is only effective the first time a particular Apache Karaf instance boots up. Any changes made subsequently to the
featuresRepositories setting and the featuresBoot setting are ignored, even if you restart the container.
You could force the container to revert back to its initial state, however, by deleting the complete contents of the
InstallDir/data/cache (thereby losing all of the container's custom settings).
Chapter 9. Deploying a Plain JAR
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Abstract
This chapter explains how to deal with plain JAR files (typically libraries) that contain no deployment metadata whatsoever. That is, a plain JAR is neither a WAR, nor an OSGi bundle.
If the plain JAR occurs as a dependency of a bundle, you must add bundle headers to the JAR . If the JAR exposes a public API, typically the best solution is to convert the existing JAR into a bundle, enabling the JAR to be shared with other bundles. This chapter describes how to perform the conversion process automatically, using the open source Bnd tool.
For more information on Bnd tool, see Bnd tools website.
9.1. Converting a JAR Using the wrap Scheme
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Overview
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You also have the option of converting a JAR into a bundle using the
wrap scheme, which can be prefixed to any existing URL format. The wrap scheme is also based on the Bnd utility.
Syntax
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The
wrap scheme has the following basic syntax:
wrap:LocationURL
wrap:LocationURL
The
wrap scheme can prefix any URL that locates a JAR. The locating part of the URL, LocationURL, is used to obtain the (non-bundlized) JAR and the URL handler for the wrap scheme then converts the JAR automatically into a bundle.
Note
The
wrap scheme also supports a more elaborate syntax, which enables you to customize the conversion by specifying a Bnd properties file or by specifying individual Bnd properties in the URL. Typically, however, the wrap scheme is used just with its default settings.
Default properties
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Because the
wrap scheme is based on the Bnd utility, it uses exactly the same default properties to generate the bundle as Bnd does—see ???.
Wrap and install
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The following example shows how you can use a single console command to download the plain
commons-logging JAR from a remote Maven repository, convert it into an OSGi bundle on the fly, and then install it and start it in the OSGi container:
JBossFuse:karaf@root> osgi:install -s wrap:mvn:commons-logging/commons-logging/1.1.1
JBossFuse:karaf@root> osgi:install -s wrap:mvn:commons-logging/commons-logging/1.1.1Reference
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The
wrap scheme is provided by the Pax project, which is the umbrella project for a variety of open source OSGi utilities. For full documentation on the wrap scheme, see the Wrap Protocol reference page.
Chapter 10. OSGi Bundle Tutorials
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Abstract
This chapter presents tutorials for Apache Camel and Apache CXF applications. Each tutorial describes how to generate, build, run, and deploy an application as an OSGi bundle.
10.1. Generating and Running an EIP Bundle
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Overview
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This section explains how to generate, build, and run a complete Apache Camel example as an OSGi bundle, where the starting point code is generated with the help of a Maven archetype.
Prerequisites
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In order to generate a project using an Red Hat JBoss Fuse Maven archetype, you must have the following prerequisites:
- Maven installation—Maven is a free, open source build tool from Apache. You can download the latest version from http://maven.apache.org/download.html (minimum is 3.x).
- Internet connection—whilst performing a build, Maven dynamically searches external repositories and downloads the required artifacts on the fly. In order for this to work, your build machine must be connected to the Internet.
- fusesource Maven repository is configured—in order to locate the archetypes, Maven's
settings.xmlfile must be configured with the location of thefusesourceMaven repository. For details of how to set this up, see the section called “Adding the Red Hat JBoss Fuse repository”.
Generating an EIP bundle
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The
karaf-camel-cbr-archetype archetype creates a router project, which is configured to deploy as a bundle. To generate a Maven project with the coordinates, org.fusesource.example:camel-bundle, enter the following command:
Note
The backslash character,
\, indicates line continuation on Linux and UNIX operating systems. On Windows platforms, you must omit the backslash character and put all of the arguments on a single line.
The result of this command is a directory,
ProjectDir/camel-bundle, containing the files for the generated bundle project.
Running the EIP bundle
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To install and run the generated
camel-bundle project, perform the following steps:
- Build the project—open a command prompt and change directory to
ProjectDir/camel-bundle. Use Maven to build the demonstration by entering the following command:mvn install
mvn installCopy to Clipboard Copied! Toggle word wrap Toggle overflow If this command runs successfully, theProjectDir/camel-bundle/targetdirectory should contain the bundle file,camel-bundle.jarand the bundle will also be installed in the local Maven repository. - Install prerequisite features (optional)—by default, the
camel-corefeature and some related features are pre-installed in the OSGi container. But many of the Apache Camel components are not installed by default. To check which features are available and whether or not they are installed, enter the following console command:JBossFuse:karaf@root> features:list
JBossFuse:karaf@root> features:listCopy to Clipboard Copied! Toggle word wrap Toggle overflow Apache Camel features are identifiable by thecamel-prefix. For example, if one of your routes requires the HTTP component, you can make sure that it is installed in the OSGi container by issuing the following console command:JBossFuse:karaf@root> features:install camel-http
JBossFuse:karaf@root> features:install camel-httpCopy to Clipboard Copied! Toggle word wrap Toggle overflow - Install and start the camel-bundle bundle—at the Red Hat JBoss Fuse console, enter the following command to install the bundle from the local Maven repository (see Section A.3, “Mvn URL Handler”):
JBossFuse:karaf@root> osgi:install -s mvn:org.fusesource.example/camel-bundle/1.0-SNAPSHOT
JBossFuse:karaf@root> osgi:install -s mvn:org.fusesource.example/camel-bundle/1.0-SNAPSHOTCopy to Clipboard Copied! Toggle word wrap Toggle overflow - Provide the route with file data to process—after the route has started, you should find the following directory under your JBoss Fuse installation:
InstallDir/work/cbr/input
InstallDir/work/cbr/inputCopy to Clipboard Copied! Toggle word wrap Toggle overflow To initiate content routing in this example, copy the provided data files from theProjectDir/camel-bundle/src/main/fabric8/datadirectory into theInstallDir/work/cbr/inputdirectory. - View the output—after a second or two, the data files disappear from the
work/cbr/inputdirectory, as the route moves the data files into various sub-directories of thework/cbr/outputdirectory. - Stop the camel-bundle bundle—to stop the
camel-bundlebundle, you first need to discover the relevant bundle number. To find the bundle number, enter the following console command:JBossFuse:karaf@root> osgi:list
JBossFuse:karaf@root> osgi:listCopy to Clipboard Copied! Toggle word wrap Toggle overflow At the end of the listing, you should see an entry like the following:[ 265] [Active ] [Created ] [ ] [ 80] JBoss Fuse Quickstart: camel-cbr (1.0.0.SNAPSHOT)
[ 265] [Active ] [Created ] [ ] [ 80] JBoss Fuse Quickstart: camel-cbr (1.0.0.SNAPSHOT)Copy to Clipboard Copied! Toggle word wrap Toggle overflow Where, in this example, the bundle number is 265. To stop this bundle, enter the following console command:JBossFuse:karaf@root> osgi:stop 265
JBossFuse:karaf@root> osgi:stop 265Copy to Clipboard Copied! Toggle word wrap Toggle overflow
10.2. Generating and Running a Web Services Bundle
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Overview
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This section explains how to generate, build, and run a complete Apache CXF example as a bundle in the OSGi container, where the starting point code is generated with the help of a Maven archetype.
Prerequisites
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In order to generate a project using a Red Hat JBoss Fuse Maven archetype, you must have the following prerequisites:
- Maven installation—Maven is an open source build tool from Apache. You can download the latest version from http://maven.apache.org/download.html (minimum is 3.x).
- Internet connection—whilst performing a build, Maven dynamically searches external repositories and downloads the required artifacts on the fly. In order for this to work, your build machine must be connected to the Internet.
- fusesource Maven repository is configured—in order to locate the archetypes, Maven's
settings.xmlfile must be configured with the location of thefusesourceMaven repository. For details of how to set this up, see the section called “Adding the Red Hat JBoss Fuse repository”.
Generating a Web services bundle
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The
karaf-soap-archetype archetype creates a project for building a Java-first JAX-WS application that can be deployed into the OSGi container. To generate a Maven project with the coordinates, org.fusesource.example:cxf-code-first-bundle, enter the following command:
Note
The backslash character,
\, indicates line continuation on Linux and UNIX operating systems. On Windows platforms, you must omit the backslash character and put all of the arguments on a single line.
The result of this command is a directory,
ProjectDir/cxf-code-first-bundle, containing the files for the generated bundle project.
Modifying the bundle instructions
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Typically, you will need to modify the instructions for the Maven bundle plug-in in the POM file. In particular, the default
Import-Package element generated by the karaf-soap-archetype archetype is not configured to scan the project's Java source files. In most cases, however, you would want the Maven bundle plug-in to perform this automatic scanning in order to ensure that the bundle imports all of the packages needed by your code.
To enable the
Import-Package scanning feature, simply add the wildcard, *, as the last item in the comma-separated list inside the Import-Package element, as shown in the following example:
Example 10.1. Import-Package Instruction with Wildcard
Running the Web services bundle
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To install and run the generated
cxf-code-first-bundle project, perform the following steps:
- Build the project—open a command prompt and change directory to
ProjectDir/cxf-code-first-bundle. Use Maven to build the demonstration by entering the following command:mvn install
mvn installCopy to Clipboard Copied! Toggle word wrap Toggle overflow If this command runs successfully, theProjectDir/cxf-code-first-bundle/targetdirectory should contain the bundle file,cxf-code-first-bundle.jar. - Install and start the cxf-code-first-bundle bundle—at the Red Hat JBoss Fuse console, enter the following command to install the bundle from your local Maven repository:
JBossFuse:karaf@root> osgi:install -s mvn:org.fusesource.example/cxf-code-first-bundle/1.0-SNAPSHOT
JBossFuse:karaf@root> osgi:install -s mvn:org.fusesource.example/cxf-code-first-bundle/1.0-SNAPSHOTCopy to Clipboard Copied! Toggle word wrap Toggle overflow - Test the Web serivce—to test the Web service deployed in the previous step, you can use a web browser to query the service's WSDL. Open your favourite web browser and navigate to the following URL:
http://localhost:8181/cxf/HelloWorld?wsdl
http://localhost:8181/cxf/HelloWorld?wsdlCopy to Clipboard Copied! Toggle word wrap Toggle overflow When the web service receives the query,?wsdl, it returns a WSDL description of the running service. - Stop the cxf-code-first-bundle bundle—to stop the
cxf-code-first-bundlebundle, you first need to discover the relevant bundle number. To find the bundle number, enter the following console command:JBossFuse:karaf@root> osgi:list
JBossFuse:karaf@root> osgi:listCopy to Clipboard Copied! Toggle word wrap Toggle overflow At the end of the listing, you should see an entry like the following:[ 266] [Active ] [Created ] [ ] [ 80] JBoss Fuse Quickstart: soap (1.0.0.SNAPSHOT)
[ 266] [Active ] [Created ] [ ] [ 80] JBoss Fuse Quickstart: soap (1.0.0.SNAPSHOT)Copy to Clipboard Copied! Toggle word wrap Toggle overflow Where, in this example, the bundle number is 266. To stop this bundle, enter the following console command:JBossFuse:karaf@root> osgi:stop 266
JBossFuse:karaf@root> osgi:stop 266Copy to Clipboard Copied! Toggle word wrap Toggle overflow
Part III. WAR Deployment Model
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Abstract
The Web application ARchive (WAR) is a tried and tested model for packaging and deploying applications. This approach is simple and reliable, thought not as flexible as the OSGi bundle model.
Chapter 11. Building a WAR
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Abstract
This chapter describes how to build and package a WAR using Maven.
11.1. Modifying an Existing Maven Project
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Overview
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If you already have a Maven project and you want to modify it so that it generates a WAR, perform the following steps:
Change the package type to WAR
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Configure Maven to generate a WAR by changing the package type to
war in your project's pom.xml file. Change the contents of the packaging element to war, as shown in the following example:
<project ... > ... <packaging>war</packaging> ... </project>
<project ... >
...
<packaging>war</packaging>
...
</project>
The effect of this setting is to select the Maven WAR plug-in,
maven-war-plugin, to perform packaging for this project.
Customize the JDK compiler version
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It is almost always necessary to specify the JDK version in your POM file. If your code uses any modern features of the Java language—such as generics, static imports, and so on—and you have not customized the JDK version in the POM, Maven will fail to compile your source code. It is not sufficient to set the
JAVA_HOME and the PATH environment variables to the correct values for your JDK, you must also modify the POM file.
To configure your POM file, so that it accepts the Java language features introduced in JDK 1.7, add the following
maven-compiler-plugin plug-in settings to your POM (if they are not already present):
Store resources under webapp/WEB-INF
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Resource files for the Web application are stored under the
/WEB-INF directory in the standard WAR directory layout. In order to ensure that these resources are copied into the root of the generated WAR package, store the WEB-INF directory under ProjectDir/src/main/webapp in the Maven directory tree, as follows:
In particular, note that the
web.xml file is stored at ProjectDir/src/main/webapp/WEB-INF/web.xml.
Customize the Maven WAR plug-in
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It is possible to customize the Maven WAR plug-in by adding an entry to the
plugins section of the pom.xml file. Most of the configuration options are concerned with adding additonal resources to the WAR package. For example, to include all of the resources under the src/main/resources directory (specified relative to the location of pom.xml) in the WAR package, you could add the following WAR plug-in configuration to your POM:
The preceding plug-in configuration customizes the following settings:
webXml- Specifies where to find the
web.xmlfile in the current Maven project, relative to the location ofpom.xml. The default issrc/main/webapp/WEB-INF/web.xml. webResources- Specifies additional resource files that are to be included in the generated WAR package. It can contain the following sub-elements:
webResources/resource—each resource elements specifies a set of resource files to include in the WAR.webResources/resource/directory—specifies the base directory from which to copy resource files, where this directory is specified relative to the location ofpom.xml.webResources/resource/targetPath—specifies where to put the resource files in the generated WAR package.webResources/resource/includes—uses an Ant-style wildcard pattern to specify explicitly which resources should be included in the WAR.webResources/resource/excludes—uses an Ant-style wildcard pattern to specify explicitly which resources should be excluded from the WAR (exclusions have priority over inclusions).
For complete details of how to configure the Maven WAR plug-in, see http://maven.apache.org/plugins/maven-war-plugin/index.html.
Note
Do not use version 2.1 of the
maven-war-plugin plug-in, which has a bug that causes two copies of the web.xml file to be inserted into the generated .war file.
Building the WAR
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To build the WAR defined by the Maven project, open a command prompt, go to the project directory (that is, the directory containing the
pom.xml file), and enter the following Maven command:
mvn install
mvn install
The effect of this command is to compile all of the Java source files, to generate a WAR under the
ProjectDir/target directory, and then to install the generated WAR in the local Maven repository.
11.2. Bootstrapping a CXF Servlet in a WAR
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Overview
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A simple way to bootstrap Apache CXF in a WAR is to configure
web.xml to use the standard CXF servlet, org.apache.cxf.transport.servlet.CXFServlet.
Example
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For example, the following
web.xml file shows how to configure the CXF servlet, where all Web service addresses accessed through this servlet would be prefixed by /services/ (as specified by the value of servlet-mapping/url-pattern):
cxf-servlet.xml file
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In addition to configuring the
web.xml file, it is also necessary to configure your Web services by defining a cxf-servlet.xml file, which must be copied into the root of the generated WAR.
Alternatively, if you do not want to put
cxf-servlet.xml in the default location, you can customize its name and location, by setting the contextConfigLocation context parameter in the web.xml file. For example, to specify that Apache CXF configuration is located in WEB-INF/cxf-servlet.xml, set the following context parameter in web.xml:
11.3. Bootstrapping a Spring Context in a WAR
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Overview
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You can bootstrap a Spring context in a WAR using Spring's ContextLoaderListener class.
Bootstrapping a Spring context in a WAR
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For example, the following
web.xml file shows how to boot up a Spring application context that is initialized by the XML file, /WEB-INF/applicationContext.xml (which is the location of the context file in the generated WAR package):
Maven dependency
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In order to access the
ContextLoaderListener class from the Spring framework, you must add the following dependency to your project's pom.xml file:
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
<version>${spring-version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
<version>${spring-version}</version>
</dependency>
Where the
spring-version property specifies the version of the Spring framework you are using.
Chapter 12. Deploying a WAR
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Abstract
This chapter explains how to deploy a Web archive (WAR) file as a bundle in the OSGi container. Conversion to a bundle is performed automatically by the PAX War URL, which is based on the open source Bnd tool. The presence of a
web.xml file in the bundle signals to the container that the bundle should be deployed as a Web application.
Important
The information in this chapter pertains to deploying standard JEE WAR files into an OSGi container. For complex War files, those which combine components, such as Apache Camel and Spring, the easiest and most efficient way to deploy them into a JBoss Fuse container is to use JBoss Fuse on EAP. For details, see the JBoss Fuse on EAP documention listed under Getting Started and Adminisration on JBoss EAP on the Red Hat Customer Portal.
12.1. Converting the WAR Using the war Scheme
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Overview
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To convert a WAR file into a bundle suitable for deployment in the OSGi container, add the war: prefix to the WAR URL. The PAX War URL handler acts as a wrapper, which adds the requisite manifest headers to the WAR file.
Syntax
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The
war scheme has the following basic syntax:
war:LocationURL[?Options]
war:LocationURL[?Options]
The location URL, LocationURL, can be any of the location URLs described in Appendix A, URL Handlers (for example, an
mvn: or a file: URL). Options can be appended to the URL in the following format:
?Option=Value&Option=Value&...
?Option=Value&Option=Value&...
Or if the
war URL appears in an XML file:
?Option=Value&Option=Value&...
?Option=Value&Option=Value&...Prerequisite
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The Apache Karaf
war feature is required to convert and deploy WARs using the war: scheme. It can be installed from the container's command console using features:install war.
Deploying a WAR file
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If the WAR file is stored in a Maven repository, you can deploy it into the OSGi container using the
osgi:install command, taking a war:mvn: URL as its argument. For example, to deploy the wicket-example WAR file from a Maven repository, where the application should be accessible from the wicket Web application context, enter the following console command:
JBossFuse:karaf@root> install war:mvn:org.apache.wicket/wicket-examples/1.4.7/war?Web-ContextPath=wicket
JBossFuse:karaf@root> install war:mvn:org.apache.wicket/wicket-examples/1.4.7/war?Web-ContextPath=wicket
Alternatively, if the WAR file is stored on the filesystem, you can deploy it into the OSGi container by specifying a
war:file: URL. For example, to deploy the WAR file, wicket-example-1.4.6.war, enter the following console command:
JBossFuse:karaf@root> install war:file://wicket-examples-1.4.7.war?Web-ContextPath=wicket
JBossFuse:karaf@root> install war:file://wicket-examples-1.4.7.war?Web-ContextPath=wicketAccessing the Web application
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The WAR file is automatically installed into a Web container, which listens on the TCP port 8181 by default, and the Web container uses the Web application context specified by the
Web-ContextPath option. For example, the wicket-example WAR deployed in the preceding examples, would be accessible from the following URL:
http://localhost:8181/wicket
http://localhost:8181/wicketDefault conversion parameters
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The PAX War URL handler converts a WAR file to a special kind of OSGi bundle, which includes additional Manifest headers to support WAR deployment (for example, the
Web-ContextPath Manifest header). By default, the deployed WAR is configured as an isolated bundle (neither importing nor exporting any packages). This mimics the deployment model of a WAR inside a J2EE container, where the WAR is completely self-contained, including all of the JAR files it needs.
For details of the default conversion parameters, see Table A.2, “Default Instructions for Wrapping a WAR File”.
Customizing the conversion parameters
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The PAX War URL handler is layered over Bnd. If you want to customize the bundle headers in the Manifest file, you can either add a Bnd instruction as a URL option or you can specify a Bnd instructions file for the War URL handler to use—for details, see Section A.5, “War URL Handler”.
In particular, you might sometimes find it necessary to customize the entry for the
Bundle-ClassPath, because the default value of Bundle-ClassPath does not include all of the resources in the WAR file (see Table A.2, “Default Instructions for Wrapping a WAR File”).
References
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Support for running WARs in the OSGi container is provided by the PAX WAR Extender, which monitors each bundle as it starts and, if the bundle contains a
web.xml file, automatically deploys the WAR in a Web container. The War Protocol page has the original reference documentation for the War URL handler.
12.2. Configuring the Web Container
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Overview
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Red Hat JBoss Fuse automatically deploys WAR files into a Web container, which is implemented by the PAX Web library. You can configure the Web container through the OSGi Configuration Admin service.
Configuration file
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The Web container uses the following configuration file:
EsbInstallDir/etc/org.ops4j.pax.web.cfg
EsbInstallDir/etc/org.ops4j.pax.web.cfg
You must create this file, if it does not already exist in the
EsbInstallDir/etc/ directory.
Customizing the HTTP port
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By default, the Web container listens on the TCP port, 8181. You can change this value by editing the
etc/org.ops4j.pax.web.cfg file and setting the value of the org.osgi.service.http.port property, as follows:
# Configure the Web container org.osgi.service.http.port=8181
# Configure the Web container
org.osgi.service.http.port=8181Enabling SSL/TLS security
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The Web container is also used for deploying the Fuse Management Console. The instructions for securing the Web container with SSL/TLS are identical to the instructions for securing the Fuse Management Console with SSL/TLS. See chapter "Securing the Jetty HTTP Server" in "Security Guide" for details.
Warning
If you are planning to enable SSL/TLS security, you must ensure that you explicitly disable the SSLv3 protocol, in order to safeguard against the Poodle vulnerability (CVE-2014-3566). For more details, see Disabling SSLv3 in JBoss Fuse 6.x and JBoss A-MQ 6.x.
Reference
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The properties that you can set in the Web container's configuration file are defined by the PAX Web library. You can set the following kinds of property:
Part IV. CDI Deployment Model
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Abstract
Contexts and Dependency Injection (CDI) is a dependency injection framework based entirely on the Java language (making use of Java annotations). Although originally developed for J2EE platforms (such as JBoss EAP), CDI is also supported in Apache Karaf. Pax CDI provides an adapter layer that makes it possible to integrate CDI applications in the OSGi container.
Chapter 13. Contexts and Dependency Injection (CDI)
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13.1. Introduction to CDI
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13.1.1. About Contexts and Dependency Injection (CDI)
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Contexts and Dependency Injection (CDI) 1.2 is a JSR specification, which defines a general-purpose dependency injection framework in the Java language. Although originally conceived for the Java EE platform, CDI can also be used in the context of an OSGi container, provided the requisite adapter layer (a combination of Pax CDI and JBoss Weld) is installed and enabled.
CDI 1.2 release is treated as a maintenance release of 1.1. Details about CDI 1.1 can be found in JSR 346: Contexts and Dependency Injection for Java™ EE 1.1.
JBoss Fuse includes Weld, which is the reference implementation of JSR-346:Contexts and Dependency Injection for Java™ EE 1.1.
Benefits of CDI
The benefits of CDI include:
- Simplifying and shrinking your code base by replacing big chunks of code with annotations.
- Flexibility, allowing you to disable and enable injections and events, use alternative beans, and inject non-CDI objects easily.
-
Optionally, allowing you to include
beans.xmlin yourMETA-INF/orWEB-INF/directory if you need to customize the configuration to differ from the default. The file can be empty. - Simplifying packaging and deployments and reducing the amount of XML you need to add to your deployments.
- Providing lifecycle management via contexts. You can tie injections to requests, sessions, conversations, or custom contexts.
- Providing type-safe dependency injection, which is safer and easier to debug than string-based injection.
- Decoupling interceptors from beans.
- Providing complex event notification.
13.1.2. JBoss Weld CDI Implementation
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Weld is the reference implementation of CDI, which is defined in JSR 346: Contexts and Dependency Injection for Java™ EE 1.1. Weld was inspired by Seam 2 and other dependency injection frameworks, and is included in JBoss Fuse.
13.2. Use CDI
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13.2.1. Enable CDI in the Apache Karaf Container
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CDI is not enabled by default in the Apache Karaf container. To enable CDI in Karaf, follow the instructions in Section 14.2, “Enabling Pax CDI”.
13.2.2. Use CDI to Develop an Application
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Contexts and Dependency Injection (CDI) gives you tremendous flexibility in developing applications, reusing code, adapting your code at deployment or run-time, and unit testing. JBoss Fuse includes Weld, the reference implementation of CDI. These tasks show you how to use CDI in your enterprise applications.
13.2.2.1. Exclude Beans From the Scanning Process
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One of the features of Weld, the JBoss Fuse implementation of CDI, is the ability to exclude classes in your archive from scanning, having container lifecycle events fired, and being deployed as beans. This is not part of the JSR-346 specification.
The following example has several <weld:exclude> tags:
- 1
- The first one excludes all Swing classes.
- 2
- The second excludes Google Web Toolkit classes if Google Web Toolkit is not installed.
- 3
- The third excludes classes which end in the string
Blether(using a regular expression), if the system property verbosity is set tolow. - 4
- The fourth excludes Java Server Faces (JSF) classes if Wicket classes are present and the viewlayer system property is not set.
The formal specification of Weld-specific configuration options can be found at http://jboss.org/schema/weld/beans_1_1.xsd.
13.2.2.2. Use an Injection to Extend an Implementation
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You can use an injection to add or change a feature of your existing code.
The following example adds a translation ability to an existing class, and assumes you already have a Welcome class, which has a method buildPhrase. The buildPhrase method takes as an argument the name of a city, and outputs a phrase like "Welcome to Boston!".
Example: Inject a Translator Bean Into the Welcome Class
The following injects a hypothetical Translator object into the Welcome class. The Translator object can be an EJB stateless bean or another type of bean, which can translate sentences from one language to another. In this instance, the Translator is used to translate the entire greeting, without modifying the original Welcome class. The Translator is injected before the buildPhrase method is called.
13.2.3. Ambiguous or Unsatisfied Dependencies
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Ambiguous dependencies exist when the container is unable to resolve an injection to exactly one bean.
Unsatisfied dependencies exist when the container is unable to resolve an injection to any bean at all.
The container takes the following steps to try to resolve dependencies:
- It resolves the qualifier annotations on all beans that implement the bean type of an injection point.
- It filters out disabled beans. Disabled beans are @Alternative beans which are not explicitly enabled.
In the event of an ambiguous or unsatisfied dependency, the container aborts deployment and throws an exception.
To fix an ambiguous dependency, see Use a Qualifier to Resolve an Ambiguous Injection.
13.2.3.1. Qualifiers
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Qualifiers are annotations used to avoid ambiguous dependencies when the container can resolve multiple beans, which fit into an injection point. A qualifier declared at an injection point provides the set of eligible beans, which declare the same Qualifier.
Qualifiers have to be declared with a retention and target as shown in the example below.
Example: Define the @Synchronous and @Asynchronous Qualifiers
@Qualifier
@Retention(RUNTIME)
@Target({TYPE, METHOD, FIELD, PARAMETER})
public @interface Synchronous {}
@Qualifier
@Retention(RUNTIME)
@Target({TYPE, METHOD, FIELD, PARAMETER})
public @interface Synchronous {}@Qualifier
@Retention(RUNTIME)
@Target({TYPE, METHOD, FIELD, PARAMETER})
public @interface Asynchronous {}
@Qualifier
@Retention(RUNTIME)
@Target({TYPE, METHOD, FIELD, PARAMETER})
public @interface Asynchronous {}Example: Use the @Synchronous and @Asynchronous Qualifiers
@Synchronous
public class SynchronousPaymentProcessor implements PaymentProcessor {
public void process(Payment payment) { ... }
}
@Synchronous
public class SynchronousPaymentProcessor implements PaymentProcessor {
public void process(Payment payment) { ... }
}@Asynchronous
public class AsynchronousPaymentProcessor implements PaymentProcessor {
public void process(Payment payment) { ... }
}
@Asynchronous
public class AsynchronousPaymentProcessor implements PaymentProcessor {
public void process(Payment payment) { ... }
}13.2.3.2. Use a Qualifier to Resolve an Ambiguous Injection
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You can resolve an ambiguous injection using a qualifier. Read more about ambiguous injections at Ambiguous or Unsatisfied Dependencies.
The following example is ambiguous and features two implementations of Welcome, one which translates and one which does not. The injection needs to be specified to use the translating Welcome.
Example: Ambiguous injection
Resolve an Ambiguous Injection with a Qualifier
To resolve the ambiguous injection, create a qualifier annotation called @Translating:
@Qualifier @Retention(RUNTIME) @Target({TYPE,METHOD,FIELD,PARAMETERS}) public @interface Translating{}@Qualifier @Retention(RUNTIME) @Target({TYPE,METHOD,FIELD,PARAMETERS}) public @interface Translating{}Copy to Clipboard Copied! Toggle word wrap Toggle overflow Annotate your translating Welcome with the @Translating annotation:
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Request the translating Welcome in your injection. You must request a qualified implementation explicitly, similar to the factory method pattern. The ambiguity is resolved at the injection point.
Copy to Clipboard Copied! Toggle word wrap Toggle overflow
13.2.4. Managed Beans
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Managed Beans are defined as container-managed objects with minimal programming restrictions, otherwise known by the acronym POJO (Plain Old Java Object). They support a small set of basic services, such as resource injection, lifecycle callbacks, and interceptors. Companion specifications, such as EJB and CDI, build on this basic model.
With very few exceptions, almost every concrete Java class that has a constructor with no parameters (or a constructor designated with the annotation @Inject) is a bean.
13.2.4.1. Types of Classes That are Beans
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A managed bean is a Java class. The basic lifecycle and semantics of a managed bean are defined by the Managed Beans specification. You can explicitly declare a managed bean by annotating the bean class @ManagedBean, but in CDI you do not need to. According to the specification, the CDI container treats any class that satisfies the following conditions as a managed bean:
- It is not a non-static inner class.
-
It is a concrete class, or is annotated
@Decorator. -
It is not annotated with an EJB component-defining annotation or declared as an EJB bean class in
ejb-jar.xml. -
It does not implement interface
javax.enterprise.inject.spi.Extension. -
It has either a constructor with no parameters, or a constructor annotated with
@Inject.
The unrestricted set of bean types for a managed bean contains the bean class, every superclass and all interfaces it implements directly or indirectly.
If a managed bean has a public field, it must have the default scope @Dependent.
13.2.4.2. Use CDI to Inject an Object Into a Bean
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CDI is activated automatically if CDI components are detected in an application. If you wish to customize your configuration to differ from the default, you can include META-INF/beans.xml or WEB-INF/beans.xml to your deployment archive.
Inject Objects into Other Objects
To obtain an instance of a class, annotate the field with
@Injectwithin your bean:public class TranslateController { @Inject TextTranslator textTranslator; ...public class TranslateController { @Inject TextTranslator textTranslator; ...Copy to Clipboard Copied! Toggle word wrap Toggle overflow Use your injected object’s methods directly. Assume that TextTranslator has a method
translate:// in TranslateController class public void translate() { translation = textTranslator.translate(inputText); }// in TranslateController class public void translate() { translation = textTranslator.translate(inputText); }Copy to Clipboard Copied! Toggle word wrap Toggle overflow Use an injection in the constructor of a bean. You can inject objects into the constructor of a bean as an alternative to using a factory or service locator to create them:
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Use the
Instance(<T>)interface to get instances programatically. TheInstanceinterface can return an instance of TextTranslator when parameterized with the bean type.@Inject Instance<TextTranslator> textTranslatorInstance; ... public void translate() { textTranslatorInstance.get().translate(inputText); }@Inject Instance<TextTranslator> textTranslatorInstance; ... public void translate() { textTranslatorInstance.get().translate(inputText); }Copy to Clipboard Copied! Toggle word wrap Toggle overflow
When you inject an object into a bean, all of the object’s methods and properties are available to your bean. If you inject into your bean’s constructor, instances of the injected objects are created when your bean’s constructor is called, unless the injection refers to an instance that already exists. For instance, a new instance would not be created if you inject a session-scoped bean during the lifetime of the session.
13.2.5. Contexts and Scopes
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A context, in terms of CDI, is a storage area that holds instances of beans associated with a specific scope.
A scope is the link between a bean and a context. A scope/context combination may have a specific lifecycle. Several pre-defined scopes exist, and you can create your own. Examples of pre-defined scopes are @RequestScoped, @SessionScoped, and @ConversationScope.
13.2.5.1. Available Contexts
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| Context | Description |
|---|---|
| @Dependent | The bean is bound to the lifecycle of the bean holding the reference. |
| @ApplicationScoped | The bean is bound to the lifecycle of the application. |
| @RequestScoped | The bean is bound to the lifecycle of the request. |
| @SessionScoped | The bean is bound to the lifecycle of the session. |
| @ConversationScoped | The bean is bound to the lifecycle of the conversation. The conversation scope is between the lengths of the request and the session, and is controlled by the application. |
| Custom scopes | If the above contexts do not meet your needs, you can define custom scopes. |
13.2.6. Bean Lifecycle
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This task shows you how to save a bean for the life of a request.
The default scope for an injected bean is @Dependent. This means that the bean’s lifecycle is dependent upon the lifecycle of the bean that holds the reference. Several other scopes exist, and you can define your own scopes. For more information, see “Contexts and Scopes”.
Manage Bean Lifecycles
Annotate the bean with the desired scope:
Your bean is saved in the context relating to the scope that you specify, and lasts as long as the scope applies.
13.2.6.1. Use a Producer Method
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This task shows how to use producer methods to produce a variety of different objects that are not beans for injection.
Example: Use a producer method instead of an alternative, to allow polymorphism after deployment
The @Preferred annotation in the example is a qualifier annotation. For more information about qualifiers, see Qualifiers.
The following injection point has the same type and qualifier annotations as the producer method, so it resolves to the producer method using the usual CDI injection rules. The producer method is called by the container to obtain an instance to service this injection point.
@Inject @Preferred PaymentStrategy paymentStrategy;
@Inject @Preferred PaymentStrategy paymentStrategy;Example: Assign a scope to a producer method
The default scope of a producer method is @Dependent. If you assign a scope to a bean, it is bound to the appropriate context. The producer method in this example is only called once per session.
@Produces @Preferred @SessionScoped
public PaymentStrategy getPaymentStrategy() {
...
}
@Produces @Preferred @SessionScoped
public PaymentStrategy getPaymentStrategy() {
...
}Example: Use an injection inside a producer method
Objects instantiated directly by an application cannot take advantage of dependency injection and do not have interceptors. However, you can use dependency injection into the producer method to obtain bean instances.
If you inject a request-scoped bean into a session-scoped producer, the producer method promotes the current request-scoped instance into session scope. This is almost certainly not the desired behavior, so use caution when you use a producer method in this way.
Note
The scope of the producer method is not inherited from the bean that declares the producer method.
Producer methods allow you to inject non-bean objects and change your code dynamically.
13.2.7. Named Beans
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You can name a bean by using the @Named annotation. Naming a bean allows you to use it directly in Java Server Faces (JSF) and Expression Language (EL).
The @Named annotation takes an optional parameter, which is the bean name. If this parameter is omitted, the bean name defaults to the class name of the bean with its first letter converted to lower-case.
13.2.7.1. Use Named Beans
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Configure Bean Names Using the @Named Annotation
Use the
@Namedannotation to assign a name to a bean.Copy to Clipboard Copied! Toggle word wrap Toggle overflow In the example above, the default name would be
greeterBeanif no name had been specified.- In the context of Camel CDI, the named bean is automatically added to the registry and can be accessed from a Camel route, as follows:
from("direct:inbound").bean("greeter");from("direct:inbound").bean("greeter");Copy to Clipboard Copied! Toggle word wrap Toggle overflow
13.2.8. Alternative Beans
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Alternatives are beans whose implementation is specific to a particular client module or deployment scenario.
By default, @Alternative beans are disabled. They are enabled for a specific bean archive by editing its beans.xml file.
Example: Defining Alternatives
This alternative defines a implementation of both @Synchronous PaymentProcessor and @Asynchronous PaymentProcessor, all in one:
13.2.8.1. Override an Injection with an Alternative
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You can use alternative beans to override existing beans. They can be thought of as a way to plug in a class which fills the same role, but functions differently. They are disabled by default.
This task shows you how to specify and enable an alternative.
Override an Injection
This task assumes that you already have a TranslatingWelcome class in your project, but you want to override it with a "mock" TranslatingWelcome class. This would be the case for a test deployment, where the true Translator bean cannot be used.
Define the alternative.
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Activate the substitute implementation by adding the fully-qualified class name to your
META-INF/beans.xmlorWEB-INF/beans.xmlfile.<beans> <alternatives> <class>com.acme.MockTranslatingWelcome</class> </alternatives> </beans><beans> <alternatives> <class>com.acme.MockTranslatingWelcome</class> </alternatives> </beans>Copy to Clipboard Copied! Toggle word wrap Toggle overflow
The alternative implementation is now used instead of the original one.
13.2.9. Stereotypes
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In many systems, use of architectural patterns produces a set of recurring bean roles. A stereotype allows you to identify such a role and declare some common metadata for beans with that role in a central place.
A stereotype encapsulates any combination of:
- Default scope
- A set of interceptor bindings
A stereotype can also specify either:
- All beans where the stereotypes are defaulted bean EL names
- All beans where the stereotypes are alternatives
A bean may declare zero, one, or multiple stereotypes. A stereotype is an @Stereotype annotation that packages several other annotations. Stereotype annotations may be applied to a bean class, producer method, or field.
A class that inherits a scope from a stereotype may override that stereotype and specify a scope directly on the bean.
In addition, if a stereotype has a @Named annotation, any bean it is placed on has a default bean name. The bean may override this name if the @Named annotation is specified directly on the bean. For more information about named beans, see Named Beans.
13.2.9.1. Use Stereotypes
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Without stereotypes, annotations can become cluttered. This task shows you how to use stereotypes to reduce the clutter and streamline your code.
Example: Annotation clutter
Define and Use Stereotypes
Define the stereotype.
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Use the stereotype.
Copy to Clipboard Copied! Toggle word wrap Toggle overflow
13.2.10. Observer Methods
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Observer methods receive notifications when events occur.
CDI also provides transactional observer methods, which receive event notifications during the before completion or after completion phase of the transaction in which the event was fired.
13.2.10.1. Transactional Observers
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Transactional observers receive the event notifications before or after the completion phase of the transaction in which the event was raised. Transactional observers are important in a stateful object model because state is often held for longer than a single atomic transaction.
There are five kinds of transactional observers:
- IN_PROGRESS: By default, observers are invoked immediately.
- AFTER_SUCCESS: Observers are invoked after the completion phase of the transaction, but only if the transaction completes successfully.
- AFTER_FAILURE: Observers are invoked after the completion phase of the transaction, but only if the transaction fails to complete successfully.
- AFTER_COMPLETION: Observers are invoked after the completion phase of the transaction.
- BEFORE_COMPLETION: Observers are invoked before the completion phase of the transaction.
The following observer method refreshes a query result set cached in the application context, but only when transactions that update the Category tree are successful:
public void refreshCategoryTree(@Observes(during = AFTER_SUCCESS) CategoryUpdateEvent event) { ... }
public void refreshCategoryTree(@Observes(during = AFTER_SUCCESS) CategoryUpdateEvent event) { ... }Assume we have cached a JPA query result set in the application scope:
Occasionally a Product is created or deleted. When this occurs, we need to refresh the Product catalog. But we have to wait for the transaction to complete successfully before performing this refresh.
The bean that creates and deletes Products triggers events, for example:
The Catalog can now observe the events after successful completion of the transaction:
13.2.10.2. Fire and Observe Events
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Example: Fire an event
The following code shows an event being injected and used in a method.
Example: Fire an event with a qualifier
You can annotate your event injection with a qualifier, to make it more specific. For more information about qualifiers, see Qualifiers.
Example: Observe an event
To observe an event, use the @Observes annotation.
public class AccountObserver {
void checkTran(@Observes Withdrawal w) {
...
}
}
public class AccountObserver {
void checkTran(@Observes Withdrawal w) {
...
}
}You can use qualifiers to observe only specific types of events.
public class AccountObserver {
void checkTran(@Observes @Suspicious Withdrawal w) {
...
}
}
public class AccountObserver {
void checkTran(@Observes @Suspicious Withdrawal w) {
...
}
}13.2.11. Interceptors
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Interceptors allow you to add functionality to the business methods of a bean without modifying the bean’s method directly. The interceptor is executed before any of the business methods of the bean. Interceptors are defined as part of the Enterprise JavaBeans specification, which can be found at https://jcp.org/aboutJava/communityprocess/final/jsr318/index.html.
CDI enhances this functionality by allowing you to use annotations to bind interceptors to beans.
Interception points
- Business method interception: A business method interceptor applies to invocations of methods of the bean by clients of the bean.
- Lifecycle callback interception: A lifecycle callback interceptor applies to invocations of lifecycle callbacks by the container.
- Timeout method interception: A timeout method interceptor applies to invocations of the EJB timeout methods by the container.
13.2.11.1. Use Interceptors with CDI
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CDI can simplify your interceptor code and make it easier to apply to your business code.
Without CDI, interceptors have two problems:
- The bean must specify the interceptor implementation directly.
- Every bean in the application must specify the full set of interceptors in the correct order. This makes adding or removing interceptors on an application-wide basis time-consuming and error-prone.
Example: Interceptors without CDI
Use interceptors with CDI
Define the interceptor binding type:
@InterceptorBinding @Retention(RUNTIME) @Target({TYPE, METHOD}) public @interface Secure {}@InterceptorBinding @Retention(RUNTIME) @Target({TYPE, METHOD}) public @interface Secure {}Copy to Clipboard Copied! Toggle word wrap Toggle overflow Mark the interceptor implementation:
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Use the interceptor in your business code:
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Enable the interceptor in your deployment, by adding it to
META-INF/beans.xmlorWEB-INF/beans.xml:Copy to Clipboard Copied! Toggle word wrap Toggle overflow
The interceptors are applied in the order listed.
13.2.12. Decorators
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A decorator intercepts invocations from a specific Java interface, and is aware of all the semantics attached to that interface. Decorators are useful for modeling some kinds of business concerns, but do not have the generality of interceptors. A decorator is a bean, or even an abstract class, that implements the type it decorates, and is annotated with @Decorator. To invoke a decorator in a CDI application, it must be specified in the beans.xml file.
A decorator must have exactly one @Delegate injection point to obtain a reference to the decorated object.
Example: Example Decorator
13.2.13. Portable Extensions
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CDI is intended to be a foundation for frameworks, extensions, and for integration with other technologies. Therefore, CDI exposes a set of SPIs for the use of developers of portable extensions to CDI.
Extensions can provide the following types of functionality:
- Integration with Business Process Management engines
- Integration with third-party frameworks, such as Spring, Seam, GWT, or Wicket
- New technology based upon the CDI programming model
According to the JSR-346 specification, a portable extension can integrate with the container in the following ways:
- Providing its own beans, interceptors, and decorators to the container
- Injecting dependencies into its own objects using the dependency injection service
- Providing a context implementation for a custom scope
- Augmenting or overriding the annotation-based metadata with metadata from another source
13.2.14. Bean Proxies
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Clients of an injected bean do not usually hold a direct reference to a bean instance. Unless the bean is a dependent object (scope @Dependent), the container must redirect all injected references to the bean using a proxy object.
A bean proxy, which can be referred to as client proxy, is responsible for ensuring the bean instance that receives a method invocation is the instance associated with the current context. The client proxy also allows beans bound to contexts, such as the session context, to be serialized to disk without recursively serializing other injected beans.
Due to Java limitations, some Java types cannot be proxied by the container. If an injection point declared with one of these types resolves to a bean with a scope other than @Dependent, the container aborts the deployment.
Certain Java types cannot be proxied by the container. These include:
- Classes that do not have a non-private constructor with no parameters
-
Classes that are declared
finalor have afinalmethod - Arrays and primitive types
13.2.15. Use a Proxy in an Injection
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A proxy is used for injection when the lifecycles of the beans are different from each other. The proxy is a subclass of the bean that is created at run-time, and overrides all the non-private methods of the bean class. The proxy forwards the invocation onto the actual bean instance.
In this example, the PaymentProcessor instance is not injected directly into Shop. Instead, a proxy is injected, and when the processPayment() method is called, the proxy looks up the current PaymentProcessor bean instance and calls the processPayment() method on it.
Example: Proxy Injection
Chapter 14. Pax CDI and OSGi Services
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14.1. Pax CDI Architecture
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Overview
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Figure 14.1, “Pax CDI Architecture” gives an overview of the technology stack underlying Pax CDI.
Figure 14.1. Pax CDI Architecture
Pax CDI
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Pax CDI is the integration layer that makes it possible to deploy a CDI container within the Apache Karaf OSGi container.
JBoss Weld
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JBoss Weld provides the CDI implementation for the Pax CDI integration. JBoss Weld is the reference implementation for CDI and comes with its own extensive documentation, CDI Reference Implementation.
Bean bundle
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A bean bundle is an OSGi bundle that has been enabled to use Pax CDI. A bundle cannot use CDI by default, it must be explicitly enabled to do so (see the section called “Requirements and capabilities”).
CDI container
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A CDI container effectively defines the scope for a collection of managed beans under CDI, which are capable of being published and injected within this scope. In the context of OSGi, a CDI container maps to a single bundle. That is, each bean bundle gets its own CDI container.
Camel CDI and other customizations
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JBoss Fuse provides additional features that define CDI customizations (that is, non-standard CDI annotations) targeted at different aspects of middleware development. For example:
camel-cdi- Provides custom annotations for defining and injecting Camel contexts and routes. See Chapter 15, Camel CDI.
switchyard-cdi- Provides custom annotations for use with SwitchYard. For example, see the quickstart example under the following directory of your JBoss Fuse installation:
quickstarts/switchyard/camel-bus-cdi
quickstarts/switchyard/camel-bus-cdiCopy to Clipboard Copied! Toggle word wrap Toggle overflow For more information, see chapter "Service Implementations" in "SwitchYard Development Guide". cxf-jaxrs-cdi- Provides support for CDI in JAX-RS, as defined in the JAX-RS 2.0 Specification (see section 10.2.3).
deltaspike- Apache Deltaspike is a general-purpose collection of CDI customizations.
14.2. Enabling Pax CDI
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Overview
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Pax CDI is not enabled by default in the Karaf container in JBoss Fuse, so you must enable it explicitly. There are two aspects of enabling Pax CDI in the Karaf container: first, installing the requisite Karaf features in the container; second, enabling CDI for a particular bundle, by adding the
Require-Capability header to the bundle's manifest (turning the bundle into a bean bundle).
Pax CDI features
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To make Pax CDI functionality available in the Karaf container, install the requisite Karaf features into your container. JBoss Fuse provides the following Karaf features for Pax CDI:
pax-cdi- Deploys the core components of Pax CDI. This feature must be combined with the
pax-cdi-weldCDI implementation. pax-cdi-weld- Deploys the JBoss Weld CDI implementation (which is the only CDI implementation supported on JBoss Fuse)
pax-cdi-web- Adds support for deploying a CDI application as a Web application (that is, deploying the CDI application into the Pax Web Jetty container). This enables support for the CDI features associated with servlet deployment, such as session-scoped beans, request-scoped beans, injection into servlets, and so on. This feature must be combined with the
pax-cdi-web-weldfeature (CDI implementation). pax-cdi-web-weld- Deploys the JBoss Weld CDI implementation for Web applications.
Requirements and capabilities
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CDI requires you to organize your Java code in a very specific way, so it cannot be enabled arbitrarily for any bundle. It only makes sense to enable CDI for each bundle that needs it, not for the entire container. Hence, it is necessary to use an OSGi extension mechanism that switches on the CDI capability on a bundle-by-bundle basis. The relevant OSGi mechanism is known as the requirements and capabilities mechanism.
The CDI capability is provided by the relevant Pax CDI packages (installed as Karaf features); and the CDI requirement is specified for each bundle by adding a
Require-Capability bundle header to the bundle's manifest file. For example, to enable the base Pax CDI functionality, you would add the following Require-Capability header to the bundle's manifest file:
Require-Capability : osgi.extender; filter:="(osgi.extender=pax.cdi)"
Require-Capability : osgi.extender; filter:="(osgi.extender=pax.cdi)"
A bundle that includes the preceding
Require-Capability bundle header effectively becomes a bean bundle (a CDI enabled bundle).
How to enable Pax CDI in Apache Karaf
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To enable Pax CDI in Apache Karaf, perform the following steps:
- Add the required
pax-cdiandpax-cdi-weldfeatures to the Karaf container, as follows:JBossFuse:karaf@root> features:install pax-cdi pax-cdi-weld
JBossFuse:karaf@root> features:install pax-cdi pax-cdi-weldCopy to Clipboard Copied! Toggle word wrap Toggle overflow - When the Pax CDI features are installed in the Karaf container, this is not sufficient to enable CDI. You must also explicitly enable Pax CDI in each bundle that uses CDI (so that it becomes a bean bundle). To enable Pax CDI in a bundle, open the
pom.xmlfile in your bundle's Maven project and add the followingRequire-Capabilityelement to the configuration of the Maven bundle plug-in:Copy to Clipboard Copied! Toggle word wrap Toggle overflow - To access the CDI annotations in Java, you must add a dependency on the CDI API package. Edit your bundle's POM file,
pom.xml, to add the CDI API package as a Maven dependency:Copy to Clipboard Copied! Toggle word wrap Toggle overflow - Rebuild your bundle in the usual way for your Maven project. For example, using the command:
mvn clean install
mvn clean installCopy to Clipboard Copied! Toggle word wrap Toggle overflow - Deploy the bundle to the Karaf container in the usual way (for example, using the
osgi:installconsole command).
14.3. OSGi Services Extension
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Overview
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Pax CDI also provides an integration with OSGi services, enabling you to reference an OSGi service or to publish an OSGi service using CDI annotations. This capability is provided by the Pax CDI OSGi Services Extension, which is not enabled by default.
Enabling the OSGi Services Extension
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To enable the Pax CDI OSGi Services Extension, you must include the following bundle header in the manifest file:
Require-Capability : org.ops4j.pax.cdi.extension; filter:="(extension=pax-cdi-extension)"
Require-Capability : org.ops4j.pax.cdi.extension; filter:="(extension=pax-cdi-extension)"
In a Maven project, you would normally add a
Require-Capability element to the configuration of the Maven bundle plug-in. For example, to add both the Pax CDI Extender and the Pax CDI OSGi Services Extension to the bundle, configure your project's POM file, pom.xml, as follows:
Maven dependency for the OSGi Services extensions API
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To access the OSGi Services annotations in your Java code, you need to add a dependency on the
pax-cdi-api package. Edit your bundle's POM file, pom.xml, to add the Pax CDI API package as a Maven dependency:
Injecting an OSGi Service
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You can inject an OSGi service into a field using the following annotation:
@Inject @OsgiService private IceCreamService iceCream;
@Inject @OsgiService
private IceCreamService iceCream;
Pax CDI finds the OSGi service to inject by matching the type of the OSGi service to the type of the field.
Disambiguating OSGi Services
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If there exists more than one OSGi service of a particular type, you can disambiguate the match by filtering on the OSGi service properties—for example:
@Inject @OsgiService(filter = "(&(flavour=chocolate)(lactose=false))") private IceCreamService iceCream;
@Inject @OsgiService(filter = "(&(flavour=chocolate)(lactose=false))")
private IceCreamService iceCream;
As usual for OSGi services, the properties filter is defined using LDAP filter syntax (see the section called “Matching service properties with a filter” for more details). For an example of how to set properties on an OSGi service, see the section called “Setting OSGi Service properties”.
Selecting OSGi Services at run time
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You can reference an OSGi service dynamically by injecting it as follows:
@Inject @OsgiService(dynamic = true) private Instance<IceCreamService> iceCreamServices;
@Inject
@OsgiService(dynamic = true)
private Instance<IceCreamService> iceCreamServices;
Calling
iceCreamServices.get() will return an instance of the IceCreamService service at run time. With this approach, it is possible to reference an OSGi service that is created after your bean is created.
Publishing a bean as OSGi Service with singleton scope
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You can publish an OSGi service with OSGi singleton scope (which is the default), as follows:
@OsgiServiceProvider
public class ChocolateService implements IceCreamService {
...
}
@OsgiServiceProvider
public class ChocolateService implements IceCreamService {
...
}
OSGi singleton scope means that the bean manager creates a single instance of the bean and returns that instance every time a bean instance is requested.
Publishing a bean as OSGi Service with prototype scope
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You can publish an OSGi service with OSGi prototype scope, as follows:
@OsgiServiceProvider
@PrototypeScoped
public class ChocolateService implements IceCreamService {
...
}
@OsgiServiceProvider
@PrototypeScoped
public class ChocolateService implements IceCreamService {
...
}
OSGi prototype scope means that the bean manager creates a new bean instance every time a bean instance is requested.
Publishing a bean as OSGi Service with bundle scope
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You can publish an OSGi service with bundle scope, as follows:
@OsgiServiceProvider
@BundleScoped
public class ChocolateService implements IceCreamService {
...
}
@OsgiServiceProvider
@BundleScoped
public class ChocolateService implements IceCreamService {
...
}
Bundle scope means that the bean manger creates a new bean instance for every client bundle. That is, the
@BundleScoped beans are registered with an org.osgi.framework.ServiceFactory.
Setting OSGi Service properties
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You can set properties on an OSGi service by annotating the service bean as follows:
Publishing an OSGi Service with explicit interfaces
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You can explicitly specify the Java interfaces supported by an OSGi Service bean, as follows:
@OsgiServiceProvider(classes = {ChocolateService.class, IceCreamService.class})
public class ChocolateService implements IceCreamService {
...
}
@OsgiServiceProvider(classes = {ChocolateService.class, IceCreamService.class})
public class ChocolateService implements IceCreamService {
...
}Chapter 15. Camel CDI
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15.1. Basic Features
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Overview
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The Camel CDI component provides auto-configuration for Apache Camel using CDI as the dependency injection framework, based on convention-over-configuration. It auto-detects Camel routes available in the application and provides beans for common Camel primitives like
Endpoint, ProducerTemplate or TypeConverter. It implements standard Camel bean integration so that Camel annotations like @Consume, @Produce and @PropertyInject can be used seamlessly in CDI beans. Besides, it bridges Camel events (for example RouteAddedEvent, CamelContextStartedEvent, ExchangeCompletedEvent, ...) as CDI events and provides a CDI events endpoint that can be used to consume / produce CDI events from / to Camel routes.
How to enable Camel CDI in Apache Karaf
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To enable Camel CDI in Apache Karaf, perform the following steps:
- Add the required
pax-cdi,pax-cdi-weld, andcamel-cdifeatures to the Karaf container, as follows:JBossFuse:karaf@root> features:install pax-cdi pax-cdi-weld camel-cdi
JBossFuse:karaf@root> features:install pax-cdi pax-cdi-weld camel-cdiCopy to Clipboard Copied! Toggle word wrap Toggle overflow - To enable Camel CDI in a bundle, open the
pom.xmlfile in your bundle's Maven project and add the followingRequire-Capabilityelement to the configuration of the Maven bundle plug-in:Copy to Clipboard Copied! Toggle word wrap Toggle overflow - To access the CDI annotations in Java, you must add a dependency on the CDI API package and on the Camel CDI package. Edit your bundle's POM file,
pom.xml, to add the CDI API package as a Maven dependency:Copy to Clipboard Copied! Toggle word wrap Toggle overflow - Rebuild your bundle in the usual way for your Maven project. For example, using the command:
mvn clean install
mvn clean installCopy to Clipboard Copied! Toggle word wrap Toggle overflow - Deploy the bundle to the Karaf container in the usual way (for example, using the
osgi:installconsole command).
Auto-configured Camel context
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Camel CDI automatically deploys and configures a
CamelContext bean. That CamelContext bean is automatically instantiated, configured and started (resp. stopped) when the CDI container initialises (resp. shuts down). It can be injected in the application, for example:
@Inject CamelContext context;
@Inject
CamelContext context;
The default
CamelContext bean is qualified with the built-in @Default qualifier, is scoped @ApplicationScoped and is of type DefaultCamelContext.
Note that this bean can be customised programmatically and other Camel context beans can be deployed in the application as well.
Auto-detecting Camel routes
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Camel CDI automatically collects all the
RoutesBuilder beans in the application, instantiates and add them to the CamelContext bean instance when the CDI container initialises. For example, adding a Camel route is as simple as declaring a class, for example:
Note that you can declare as many
RoutesBuilder beans as you want. Besides, RouteContainer beans are also automatically collected, instantiated and added to the CamelContext bean instance managed by Camel CDI when the container initialises.
Auto-configured Camel primitives
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Camel CDI provides beans for common Camel primitives that can be injected in any CDI beans, for example:
Camel context configuration
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If you just want to change the name of the default
CamelContext bean, you can used the @ContextName qualifier provided by Camel CDI, for example:
Else, if more customisation is needed, any
CamelContext class can be used to declare a custom Camel context bean. Then, the @PostConstruct and @PreDestroy lifecycle callbacks can be done to do the customisation, for example:
Producer and disposer methods can also be used as well to customize the Camel context bean, for example:
Similarly, producer fields can be used, for example:
This pattern can be used for example to avoid having the Camel context routes started automatically when the container initialises by calling the
setAutoStartup method, for example:
Multiple Camel contexts
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Any number of
CamelContext beans can actually be declared in the application as documented above. In that case, the CDI qualifiers declared on these CamelContext beans are used to bind the Camel routes and other Camel primitives to the corresponding Camel contexts. From example, if the following beans get declared:
The
RoutesBuilder beans qualified with @ContextName are automatically added to the corresponding CamelContext beans by Camel CDI. If no such CamelContext bean exists, it gets automatically created, as for the RouteAddedToBazCamelContext bean. Note this only happens for the @ContextName qualifier provided by Camel CDI. Hence the RouteNotAddedToAnyCamelContext bean qualified with the user-defined @MyOtherQualifier qualifier does not get added to any Camel contexts. That may be useful, for example, for Camel routes that may be required to be added later during the application execution.
Since Camel version 2.17.0, Camel CDI is capable of managing any kind of
CamelContext beans. In previous versions, it is only capable of managing beans of type CdiCamelContext so it is required to extend it.
The CDI qualifiers declared on the
CamelContext beans are also used to bind the corresponding Camel primitives, for example:
Configuration properties
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To configure the sourcing of the configuration properties used by Camel to resolve properties placeholders, you can declare a
PropertiesComponent bean qualified with @Named("properties"), for example:
If you want to use DeltaSpike configuration mechanism you can declare the following
PropertiesComponent bean:
You can see the
camel-example-cdi-properties example for a working example of a Camel CDI application using DeltaSpike configuration mechanism.
Auto-configured type converters
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CDI beans annotated with the
@Converter annotation are automatically registered into the deployed Camel contexts, for example:
Note that CDI injection is supported within the type converters.
Lazy Injection / Programmatic Lookup
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Available as of Camel 2.17
While the CDI programmatic model favors a type-safe resolution mechanism that occurs at application initialization time, it is possible to perform dynamic / lazy injection later during the application execution using the programmatic lookup mechanism.
Camel CDI provides for convenience the annotation literals corresponding to the CDI qualifiers that you can use for standard injection of Camel primitives. These annotation literals can be used in conjunction with the
javax.enterprise.inject.Instance interface which is the CDI entry point to perform lazy injection / programmatic lookup.
For example, you can use the provided annotation literal for the
@Uriqualifier to lazily lookup for Camel primitives, for example for ProducerTemplatebeans:
Or for
Endpoint beans, for example:
Similarly, you can use the provided annotation literal for the
@ContextName qualifier to lazily lookup for CamelContext beans, for example:
You can also refined the selection based on the Camel context type, for example:
Or even iterate over a selection of Camel contexts, for example:
Injecting a Camel context from Spring XML
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While CDI favors a type safe dependency injection mechanism, it may be useful to reuse existing Camel XML configurations by injecting them into a Camel CDI application. In other use cases, it might be handy to rely on the Camel XML DSL to configure its Camel context(s).
To inject by CDI a camelContext defined in Spring XML, you need to use the Java
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The string
@Resource annotation, instead of the @Inject @ContextName annotations in the Camel CDI extension. For example,
java:jboss/camel/context/simple-context is the name of the deployed context registered in the JNDI registry. simple-context is the xml:id of the camelContext element in the Spring XML file.
Important
Using the
@Inject @ContextName annotations can result in the creation of a new camelContext instead of injecting the named context, which later causes endpoint lookups to fail.
15.2. Camel Bean Integration
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Camel annotations
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As part of the Camel bean integration, Camel comes with a set of annotations that are seamlessly supported by Camel CDI. So you can use any of these annotations in your CDI beans, for example:
| Camel annotation | CDI equivalent | |
|---|---|---|
| Configuration property |
@PropertyInject("key")
String value;
|
If using DeltaSpike configuration mechanism:
@Inject @ConfigProperty(name = "key") String value;
See configuration properties for more details.
|
| Producer template injection (default Camel context) |
@Produce(uri = "mock:outbound") ProducerTemplate producer; |
@Inject
@Uri("direct:outbound")
ProducerTemplate producer;
|
| Endpoint injection (default Camel context) |
@EndpointInject(uri = "direct:inbound") Endpoint endpoint; |
@Inject
@Uri("direct:inbound")
Endpoint endpoint;
|
| Endpoint injection (Camel context by name) |
@EndpointInject(uri = "direct:inbound", context = "foo") Endpoint contextEndpoint; |
@Inject
@ContextName("foo")
@Uri("direct:inbound")
Endpoint contextEndpoint;
|
| Bean injection (by type) |
@BeanInject MyBean bean; |
@Inject MyBean bean; |
| Bean injection (by name) |
@BeanInject("foo")
MyBean bean;
|
@Inject
@Named("foo")
MyBean bean;
|
| POJO consuming |
@Consume(uri = "seda:inbound")
void consume(@Body String body) {
//...
}
|
Bean component
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You can refer to CDI beans, either by type or name, From the Camel DSL, for example with the Java Camel DSL:
class MyBean {
//...
}
from("direct:inbound").bean(MyBean.class);
class MyBean {
//...
}
from("direct:inbound").bean(MyBean.class);
Or to lookup a CDI bean by name from the Java DSL:
Referring beans from Endpoint URIs
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When configuring endpoints using the URI syntax you can refer to beans in the Registry using the
# notation. If the URI parameter value starts with a # sign then Camel CDI will lookup for a bean of the given type by name, for example:
from("jms:queue:{{destination}}?transacted=true&transactionManager=#jtaTransactionManager").to("...");
from("jms:queue:{{destination}}?transacted=true&transactionManager=#jtaTransactionManager").to("...");
Having the following CDI bean qualified with
@Named("jtaTransactionManager"):
15.3. CDI Events in Camel
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Camel events to CDI events
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Camel provides a set of management events that can be subscribed to for listening to Camel context, service, route and exchange events. Camel CDI seamlessly translates these Camel events into CDI events that can be observed using CDI observer methods, for example:
void onContextStarting(@Observes CamelContextStartingEvent event) {
// Called before the default Camel context is about to start
}
void onContextStarting(@Observes CamelContextStartingEvent event) {
// Called before the default Camel context is about to start
}
When multiple Camel contexts exist in the CDI container, the Camel context bean qualifiers, like
@ContextName, can be used to refine the observer method resolution to a particular Camel context as specified in observer resolution, for example:
Similarly, the
@Default qualifier can be used to observe Camel events for the default Camel context if multiples contexts exist, for example:
void onExchangeCompleted(@Observes @Default ExchangeCompletedEvent event) {
// Called after the exchange 'event.getExchange()' processing has completed
}
void onExchangeCompleted(@Observes @Default ExchangeCompletedEvent event) {
// Called after the exchange 'event.getExchange()' processing has completed
}
In that example, if no qualifier is specified, the
@Any qualifier is implicitly assumed, so that corresponding events for all the Camel contexts get received.
Note that the support for Camel events translation into CDI events is only activated if observer methods listening for Camel events are detected in the deployment, and that per Camel context.
CDI events endpoint
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The CDI event endpoint bridges the CDI events with the Camel routes so that CDI events can be seamlessly observed / consumed (resp. produced / fired) from Camel consumers (resp. by Camel producers).
The
CdiEventEndpoint<T> bean provided by Camel CDI can be used to observe / consume CDI events whose event type is T, for example:
@Inject
CdiEventEndpoint<String> cdiEventEndpoint;
from(cdiEventEndpoint).log("CDI event received: ${body}");
@Inject
CdiEventEndpoint<String> cdiEventEndpoint;
from(cdiEventEndpoint).log("CDI event received: ${body}");
This is equivalent to writing:
Conversely, the
CdiEventEndpoint<T> bean can be used to produce / fire CDI events whose event type is T, for example:
@Inject
CdiEventEndpoint<String> cdiEventEndpoint;
from("direct:event").to(cdiEventEndpoint).log("CDI event sent: ${body}");
@Inject
CdiEventEndpoint<String> cdiEventEndpoint;
from("direct:event").to(cdiEventEndpoint).log("CDI event sent: ${body}");
This is equivalent to writing:
Or using a Java 8 lambda expression:
The type variable
T (resp. the qualifiers) of a particular CdiEventEndpoint<T> injection point are automatically translated into the parameterized event type (resp. into the event qualifiers) for example:
When multiple Camel contexts exist in the CDI container, the Camel context bean qualifiers, like
@ContextName, can be used to qualify the CdiEventEndpoint<T> injection points, for example:
Note that the CDI event Camel endpoint dynamically adds an observer method for each unique combination of event type and event qualifiers and solely relies on the container typesafe observer resolution, which leads to an implementation as efficient as possible.
Besides, as the impedance between the typesafe nature of CDI and the dynamic nature of the Camel component model is quite high, it is not possible to create an instance of the CDI event Camel endpoint via URIs. Indeed, the URI format for the CDI event component is:
cdi-event://PayloadType<T1,...,Tn>[?qualifiers=QualifierType1[,...[,QualifierTypeN]...]]
cdi-event://PayloadType<T1,...,Tn>[?qualifiers=QualifierType1[,...[,QualifierTypeN]...]]
With the authority
PayloadType (resp. the QualifierType) being the URI escaped fully qualified name of the payload (resp. qualifier) raw type followed by the type parameters section delimited by angle brackets for payload parameterized type. Which leads to unfriendly URIs, for example:
cdi-event://org.apache.camel.cdi.example.EventPayload%3Cjava.lang.Integer%3E?qualifiers=org.apache.camel.cdi.example.FooQualifier%2Corg.apache.camel.cdi.example.BarQualifier
cdi-event://org.apache.camel.cdi.example.EventPayload%3Cjava.lang.Integer%3E?qualifiers=org.apache.camel.cdi.example.FooQualifier%2Corg.apache.camel.cdi.example.BarQualifier
But more fundamentally, that would prevent efficient binding between the endpoint instances and the observer methods as the CDI container doesn't have any ways of discovering the Camel context model during the deployment phase.
15.4. OSGi Integration
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Auto-configured OSGi integration
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The Camel context beans are automatically adapted by Camel CDI so that they are registered as OSGi services and the various resolvers (like
ComponentResolver and DataFormatResolver) integrate with the OSGi registry. That means that the Karaf Camel commands can be used to operate the Camel contexts auto-configured by Camel CDI, for example:
karaf@root()> camel:context-list Context Status Total # Failed # Inflight # Uptime ------- ------ ------- -------- ---------- ------ camel-cdi Started 1 0 0 1 minute
karaf@root()> camel:context-list
Context Status Total # Failed # Inflight # Uptime
------- ------ ------- -------- ---------- ------
camel-cdi Started 1 0 0 1 minute
See the
camel-example-cdi-osgi example, available in the list of camel examples for a working example of the Camel CDI OSGi integration.
Part V. OSGi Service Layer
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Abstract
In Red Hat JBoss Fuse, the natural way to communicate between deployed bundles is to use OSGi services. An OSGi service exposes Java methods that can be invoked by other bundles in the container.
Chapter 16. OSGi Services
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Abstract
The OSGi core framework defines the OSGi Service Layer, which provides a simple mechanism for bundles to interact by registering Java objects as services in the OSGi service registry. One of the strengths of the OSGi service model is that any Java object can be offered as a service: there are no particular constraints, inheritance rules, or annotations that must be applied to the service class. This chapter describes how to deploy an OSGi service using the OSGi blueprint container.
16.1. The Blueprint Container
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Abstract
The blueprint container is a dependency injection framework that simplifies interaction with the OSGi container. In particular, the blueprint container supports a configuration-based approach to using the OSGi service registry—for example, providing standard XML elements to import and export OSGi services.
16.1.1. Blueprint Configuration
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Location of blueprint files in a JAR file
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Relative to the root of the bundle JAR file, the standard location for blueprint configuration files is the following directory:
OSGI-INF/blueprint
OSGI-INF/blueprint
Any files with the suffix,
.xml, under this directory are interpreted as blueprint configuration files; in other words, any files that match the pattern, OSGI-INF/blueprint/*.xml.
Location of blueprint files in a Maven project
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In the context of a Maven project, ProjectDir, the standard location for blueprint configuration files is the following directory:
ProjectDir/src/main/resources/OSGI-INF/blueprint
ProjectDir/src/main/resources/OSGI-INF/blueprintBlueprint namespace and root element
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Blueprint configuration elements are associated with the following XML namespace:
http://www.osgi.org/xmlns/blueprint/v1.0.0
http://www.osgi.org/xmlns/blueprint/v1.0.0
The root element for blueprint configuration is
blueprint, so a blueprint XML configuration file normally has the following outline form:
<?xml version="1.0" encoding="UTF-8"?> <blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"> ... </blueprint>
<?xml version="1.0" encoding="UTF-8"?>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0">
...
</blueprint>
Note
In the
blueprint root element, there is no need to specify the location of the blueprint schema using an xsi:schemaLocation attribute, because the schema location is already known to the blueprint framework.
Blueprint Manifest configuration
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There are a few aspects of blueprint configuration that are controlled by headers in the JAR's manifest file,
META-INF/MANIFEST.MF, as follows:
Custom Blueprint file locations
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If you need to place your blueprint configuration files in a non-standard location (that is, somewhere other than
OSGI-INF/blueprint/*.xml), you can specify a comma-separated list of alternative locations in the Bundle-Blueprint header in the manifest file—for example:
Bundle-Blueprint: lib/account.xml, security.bp, cnf/*.xml
Bundle-Blueprint: lib/account.xml, security.bp, cnf/*.xmlMandatory dependencies
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Dependencies on an OSGi service are mandatory by default (although this can be changed by setting the
availability attribute to optional on a reference element or a reference-list element). Declaring a dependency to be mandatory means that the bundle cannot function properly without that dependency and the dependency must be available at all times.
Normally, while a blueprint container is initializing, it passes through a grace period, during which time it attempts to resolve all mandatory dependencies. If the mandatory dependencies cannot be resolved in this time (the default timeout is 5 minutes), container initialization is aborted and the bundle is not started. The following settings can be appended to the
Bundle-SymbolicName manifest header to configure the grace period:
blueprint.graceperiod- If
true(the default), the grace period is enabled and the blueprint container waits for mandatory dependencies to be resolved during initialization; iffalse, the grace period is skipped and the container does not check whether the mandatory dependencies are resolved. blueprint.timeout- Specifies the grace period timeout in milliseconds. The default is 300000 (5 minutes).
For example, to enable a grace period of 10 seconds, you could define the following
Bundle-SymbolicName header in the manifest file:
Bundle-SymbolicName: org.fusesource.example.osgi-client; blueprint.graceperiod:=true; blueprint.timeout:= 10000
Bundle-SymbolicName: org.fusesource.example.osgi-client;
blueprint.graceperiod:=true;
blueprint.timeout:= 10000
The value of the
Bundle-SymbolicName header is a semi-colon separated list, where the first item is the actual bundle symbolic name, the second item, blueprint.graceperiod:=true, enables the grace period and the third item, blueprint.timeout:= 10000, specifies a 10 second timeout.
16.1.2. Defining a Service Bean
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Overview
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Similarly to the Spring container, the blueprint container enables you to instantiate Java classes using a
bean element. You can create all of your main application objects this way. In particular, you can use the bean element to create a Java object that represents an OSGi service instance.
Blueprint bean element
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The blueprint
bean element is defined in the blueprint schema namespace, http://www.osgi.org/xmlns/blueprint/v1.0.0. The blueprint {http://www.osgi.org/xmlns/blueprint/v1.0.0}bean element should not be confused with the Spring {http://www.springframework.org/schema/beans}bean element, which has a similar syntax but is defined in a different namespace.
Note
The Spring DM specification version 2.0 or later, allows you to mix both kinds of
bean element under the beans root element, (as long as you define each bean elements using the appropriate namespace prefix).
Sample beans
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The blueprint
bean element enables you to create objects using a similar syntax to the conventional Spring bean element. One significant difference, however, is that blueprint constructor arguments are specified using the argument child element, in contrast to Spring's constructor-arg child element. The following example shows how to create a few different types of bean using blueprint's bean element:
Where the
Account class referenced by the last bean example could be defined as follows:
Differences between Blueprint and Spring
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Althought the syntax of the blueprint
bean element and the Spring bean element are similar, there are a few differences, as you can see from Table 16.1, “Comparison of Spring bean with Blueprint bean”. In this table, the XML tags (identifiers enclosed in angle brackets) refer to child elements of bean and the plain identifiers refer to attributes.
| Spring DM Attributes/Tags | Blueprint Attributes/Tags |
|---|---|
id | id |
name/<alias> | N/A |
class | class |
scope | scope=("singleton"|"prototype") |
lazy-init=("true"|"false") | activation=("eager"|"lazy") |
depends-on | depends-on |
init-method | init-method |
destroy-method | destroy-method |
factory-method | factory-bean |
factory-bean | factory-ref |
<constructor-arg> | <argument> |
<property> | <property> |
Where the default value of the blueprint
scope attribute is singleton and the default value of the blueprint activation attribute is eager.
References
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For more details on defining blueprint beans, consult the following references:
- Spring Dynamic Modules Reference Guide v2.0 (see the blueprint chapters).
- Section 121 Blueprint Container Specification, from the OSGi Compendium Services R4.2 specification.
16.1.3. Exporting a Service
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Overview
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This section describes how to export a Java object to the OSGi service registry, thus making it accessible as a service to other bundles in the OSGi container.
Exporting with a single interface
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To export a service to the OSGi service registry under a single interface name, define a
service element that references the relevant service bean, using the ref attribute, and specifies the published interface, using the interface attribute.
For example, you could export an instance of the
SavingsAccountImpl class under the org.fusesource.example.Account interface name using the blueprint configuration code shown in Example 16.1, “Sample Service Export with a Single Interface”.
Example 16.1. Sample Service Export with a Single Interface
Where the
ref attribute specifies the ID of the corresponding bean instance and the interface attribute specifies the name of the public Java interface under which the service is registered in the OSGi service registry. The classes and interfaces used in this example are shown in Example 16.2, “Sample Account Classes and Interfaces”
Example 16.2. Sample Account Classes and Interfaces
Exporting with multiple interfaces
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To export a service to the OSGi service registry under multiple interface names, define a
service element that references the relevant service bean, using the ref attribute, and specifies the published interfaces, using the interfaces child element.
For example, you could export an instance of the
SavingsAccountImpl class under the list of public Java interfaces, org.fusesource.example.Account and org.fusesource.example.SavingsAccount, using the following blueprint configuration code:
Note
The
interface attribute and the interfaces element cannot be used simultaneously in the same service element. You must use either one or the other.
Exporting with auto-export
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If you want to export a service to the OSGi service registry under all of its implemented public Java interfaces, there is an easy way of accomplishing this using the
auto-export attribute.
For example, to export an instance of the
SavingsAccountImpl class under all of its implemented public interfaces, use the following blueprint configuration code:
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"> <bean id="savings" class="org.fusesource.example.SavingsAccountImpl"/> <service ref="savings" auto-export="interfaces"/> ... </blueprint>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0">
<bean id="savings" class="org.fusesource.example.SavingsAccountImpl"/>
<service ref="savings" auto-export="interfaces"/>
...
</blueprint>
Where the
interfaces value of the auto-export attribute indicates that blueprint should register all of the public interfaces implemented by SavingsAccountImpl. The auto-export attribute can have the following valid values:
disabled- Disables auto-export. This is the default.
interfaces- Registers the service under all of its implemented public Java interfaces.
class-hierarchy- Registers the service under its own type (class) and under all super-types (super-classes), except for the
Objectclass. all-classes- Like the
class-hierarchyoption, but including all of the implemented public Java interfaces as well.
Setting service properties
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The OSGi service registry also allows you to associate service properties with a registered service. Clients of the service can then use the service properties to search for or filter services. To associate service properties with an exported service, add a
service-properties child element that contains one or more beans:entry elements (one beans:entry element for each service property).
For example, to associate the
bank.name string property with a savings account service, you could use the following blueprint configuration:
Where the
bank.name string property has the value, HighStreetBank. It is possible to define service properties of type other than string: that is, primitive types, arrays, and collections are also supported. For details of how to define these types, see Controlling the Set of Advertised Properties. in the Spring Reference Guide.
Note
Strictly speaking, the
entry element ought to belong to the blueprint namespace. The use of the beans:entry element in Spring's implementation of blueprint is non-standard.
Default service properties
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There are two service properties that might be set automatically when you export a service using the
service element, as follows:
osgi.service.blueprint.compname—is always set to theidof the service'sbeanelement, unless the bean is inlined (that is, the bean is defined as a child element of theserviceelement). Inlined beans are always anonymous.service.ranking—is automatically set, if the ranking attribute is non-zero.
Specifying a ranking attribute
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If a bundle looks up a service in the service registry and finds more than one matching service, you can use ranking to determine which of the services is returned. The rule is that, whenever a lookup matches multiple services, the service with the highest rank is returned. The service rank can be any non-negative integer, with
0 being the default. You can specify the service ranking by setting the ranking attribute on the service element—for example:
<service ref="savings" interface="org.fusesource.example.Account" ranking="10"/>
<service ref="savings" interface="org.fusesource.example.Account" ranking="10"/>Specifying a registration listener
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If you want to keep track of service registration and unregistration events, you can define a registration listener callback bean that receives registration and unregistration event notifications. To define a registration listener, add a
registration-listener child element to a service element.
For example, the following blueprint configuration defines a listener bean,
listenerBean, which is referenced by a registration-listener element, so that the listener bean receives callbacks whenever an Account service is registered or unregistered:
Where the
registration-listener element's ref attribute references the id of the listener bean, the registration-method attribute specifies the name of the listener method that receives the registration callback, and unregistration-method attribute specifies the name of the listener method that receives the unregistration callback.
The following Java code shows a sample definition of the
Listener class that receives notifications of registration and unregistration events:
The method names,
register and unregister, are specified by the registration-method and unregistration-method attributes respectively. The signatures of these methods must conform to the following syntax:
- First method argument—any type T that is assignable from the service object's type. In other words, any supertype class of the service class or any interface implemented by the service class. This argument contains the service instance, unless the service bean declares the
scopeto beprototype, in which case this argument isnull(when the scope isprototype, no service instance is available at registration time). - Second method argument—must be of either
java.util.Maptype orjava.util.Dictionarytype. This map contains the service properties associated with this service registration.
16.1.4. Importing a Service
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Overview
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This section describes how to obtain and use references to OSGi services that have been exported to the OSGi service registry. Essentially, you can use either the
reference element or the reference-list element to import an OSGi service. The key difference between these elements is not (as you might at first be tempted to think) that reference returns a single service reference, while reference-list returns a list of service references. Rather, the real difference is that the reference element is suitable for accessing stateless services, while the reference-list element is suitable for accessing stateful services.
Managing service references
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The following models for obtaining OSGi services references are supported:
Reference manager
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A reference manager instance is created by the blueprint
reference element. This element returns a single service reference and is the preferred approach for accessing stateless services. Figure 16.1, “Reference to Stateless Service” shows an overview of the model for accessing a stateless service using the reference manager.
Figure 16.1. Reference to Stateless Service
Beans in the client blueprint container get injected with a proxy object (the provided object), which is backed by a service object (the backing service) from the OSGi service registry. This model explicitly takes advantage of the fact that stateless services are interchangeable, in the following ways:
- If multiple services instances are found that match the criteria in the
referenceelement, the reference manager can arbitrarily choose one of them as the backing instance (because they are interchangeable). - If the backing service disappears, the reference manager can immediately switch to using one of the other available services of the same type. Hence, there is no guarantee, from one method invocation to the next, that the proxy remains connected to the same backing service.
The contract between the client and the backing service is thus stateless, and the client must not assume that it is always talking to the same service instance. If no matching service instances are available, the proxy will wait for a certain length of time before throwing the
ServiceUnavailable exception. The length of the timeout is configurable by setting the timeout attribute on the reference element.
Reference list manager
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A reference list manager instance is created by the blueprint
reference-list element. This element returns a list of service references and is the preferred approach for accessing stateful services. Figure 16.2, “List of References to Stateful Services” shows an overview of the model for accessing a stateful service using the reference list manager.
Figure 16.2. List of References to Stateful Services
Beans in the client blueprint container get injected with a
java.util.List object (the provided object), which contains a list of proxy objects. Each proxy is backed by a unique service instance in the OSGi service registry. Unlike the stateless model, backing services are not considered to be interchangeable here. In fact, the lifecycle of each proxy in the list is tightly linked to the lifecycle of the corresponding backing service: when a service gets registered in the OSGi registry, a corresponding proxy is synchronously created and added to the proxy list; and when a service gets unregistered from the OSGi registry, the corresponding proxy is synchronously removed from the proxy list.
The contract between a proxy and its backing service is thus stateful, and the client may assume when it invokes methods on a particular proxy, that it is always communicating with the same backing service. It could happen, however, that the backing service becomes unavailable, in which case the proxy becomes stale. Any attempt to invoke a method on a stale proxy will generate the
ServiceUnavailable exception.
Matching by interface (stateless)
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The simplest way to obtain a stateles service reference is by specifying the interface to match, using the
interface attribute on the reference element. The service is deemed to match, if the interface attribute value is a super-type of the service or if the attribute value is a Java interface implemented by the service (the interface attribute can specify either a Java class or a Java interface).
For example, to reference a stateless
SavingsAccount service (see Example 16.1, “Sample Service Export with a Single Interface”), define a reference element as follows:
Where the
reference element creates a reference manager bean with the ID, savingsRef. To use the referenced service, inject the savingsRef bean into one of your client classes, as shown.
The bean property injected into the client class can be any type that is assignable from
SavingsAccount. For example, you could define the Client class as follows:
Matching by interface (stateful)
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The simplest way to obtain a stateful service reference is by specifying the interface to match, using the
interface attribute on the reference-list element. The reference list manager then obtains a list of all the services, whose interface attribute value is either a super-type of the service or a Java interface implemented by the service (the interface attribute can specify either a Java class or a Java interface).
For example, to reference a stateful
SavingsAccount service (see Example 16.1, “Sample Service Export with a Single Interface”), define a reference-list element as follows:
Where the
reference-list element creates a reference list manager bean with the ID, savingsListRef. To use the referenced service list, inject the savingsListRef bean reference into one of your client classes, as shown.
By default, the
savingsAccountList bean property is a list of service objects (for example, java.util.List<SavingsAccount>). You could define the client class as follows:
Matching by interface and component name
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To match both the interface and the component name (bean ID) of a stateless service, specify both the
interface attribute and the component-name attribute on the reference element, as follows:
<reference id="savingsRef"
interface="org.fusesource.example.SavingsAccount"
component-name="savings"/>
<reference id="savingsRef"
interface="org.fusesource.example.SavingsAccount"
component-name="savings"/>
To match both the interface and the component name (bean ID) of a stateful service, specify both the
interface attribute and the component-name attribute on the reference-list element, as follows:
<reference-list id="savingsRef"
interface="org.fusesource.example.SavingsAccount"
component-name="savings"/>
<reference-list id="savingsRef"
interface="org.fusesource.example.SavingsAccount"
component-name="savings"/>Matching service properties with a filter
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You can select services by matching service properties against a filter. The filter is specified using the
filter attribute on the reference element or on the reference-list element. The value of the filter attribute must be an LDAP filter expression. For example, to define a filter that matches when the bank.name service property equals HighStreetBank, you could use the following LDAP filter expression:
(bank.name=HighStreetBank)
(bank.name=HighStreetBank)
To match two service property values, you can use
& conjunction, which combines expressions with a logical and.For example, to require that the foo property is equal to FooValue and the bar property is equal to BarValue, you could use the following LDAP filter expression:
(&(foo=FooValue)(bar=BarValue))
(&(foo=FooValue)(bar=BarValue))
For the complete syntax of LDAP filter expressions, see section 3.2.7 of the OSGi Core Specification.
Filters can also be combined with the
interface and component-name settings, in which case all of the specified conditions are required to match.
For example, to match a stateless service of
SavingsAccount type, with a bank.name service property equal to HighStreetBank, you could define a reference element as follows:
<reference id="savingsRef"
interface="org.fusesource.example.SavingsAccount"
filter="(bank.name=HighStreetBank)"/>
<reference id="savingsRef"
interface="org.fusesource.example.SavingsAccount"
filter="(bank.name=HighStreetBank)"/>
To match a stateful service of
SavingsAccount type, with a bank.name service property equal to HighStreetBank, you could define a reference-list element as follows:
<reference-list id="savingsRef"
interface="org.fusesource.example.SavingsAccount"
filter="(bank.name=HighStreetBank)"/>
<reference-list id="savingsRef"
interface="org.fusesource.example.SavingsAccount"
filter="(bank.name=HighStreetBank)"/>Specifying whether mandatory or optional
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By default, a reference to an OSGi service is assumed to be mandatory (see the section called “Mandatory dependencies”). It is possible, however, to customize the dependency behavior of a
reference element or a reference-list element by setting the availability attribute on the element. There are two possible values of the availability attribute: mandatory (the default), means that the dependency must be resolved during a normal blueprint container initialization; and optional, means that the dependency need not be resolved during initialization.
The following example of a
reference element shows how to declare explicitly that the reference is a mandatory dependency:
<reference id="savingsRef"
interface="org.fusesource.example.SavingsAccount"
availability="mandatory"/>
<reference id="savingsRef"
interface="org.fusesource.example.SavingsAccount"
availability="mandatory"/>Specifying a reference listener
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To cope with the dynamic nature of the OSGi environment—for example, if you have declared some of your service references to have
optional availability—it is often useful to track when a backing service gets bound to the registry and when it gets unbound from the registry. To receive notifications of service binding and unbinding events, you can define a reference-listener element as the child of either the reference element or the reference-list element.
For example, the following blueprint configuration shows how to define a reference listener as a child of the reference manager with the ID,
savingsRef:
The preceding configuration registers an instance of
org.fusesource.example.client.Listener type as a callback that listens for bind and unbind events. Events are generated whenever the savingsRef reference manager's backing service binds or unbinds.
The following example shows a sample implementation of the
Listener class:
The method names,
onBind and onUnbind, are specified by the bind-method and unbind-method attributes respectively. Both of these callback methods take an org.osgi.framework.ServiceReference argument.
16.2. Publishing an OSGi Service
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Overview
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This section explains how to generate, build, and deploy a simple OSGi service in the OSGi container. The service is a simple Hello World Java class and the OSGi configuration is defined using a blueprint configuration file.
Prerequisites
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In order to generate a project using the Maven Quickstart archetype, you must have the following prerequisites:
- Maven installation—Maven is a free, open source build tool from Apache. You can download the latest version from http://maven.apache.org/download.html (minimum is 2.0.9).
- Internet connection—whilst performing a build, Maven dynamically searches external repositories and downloads the required artifacts on the fly. In order for this to work, your build machine must be connected to the Internet.
Generating a Maven project
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The
maven-archetype-quickstart archetype creates a generic Maven project, which you can then customize for whatever purpose you like. To generate a Maven project with the coordinates, org.fusesource.example:osgi-service, enter the following command:
mvn archetype:create -DarchetypeArtifactId=maven-archetype-quickstart -DgroupId=org.fusesource.example -DartifactId=osgi-service
mvn archetype:create
-DarchetypeArtifactId=maven-archetype-quickstart
-DgroupId=org.fusesource.example
-DartifactId=osgi-service
The result of this command is a directory,
ProjectDir/osgi-service, containing the files for the generated project.
Note
Be careful not to choose a group ID for your artifact that clashes with the group ID of an existing product! This could lead to clashes between your project's packages and the packages from the existing product (because the group ID is typically used as the root of a project's Java package names).
Customizing the POM file
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You must customize the POM file in order to generate an OSGi bundle, as follows:
- Follow the POM customization steps described in Section 6.1, “Generating a Bundle Project”.
- In the configuration of the Maven bundle plug-in, modify the bundle instructions to export the
org.fusesource.example.servicepackage, as follows:Copy to Clipboard Copied! Toggle word wrap Toggle overflow
Writing the service interface
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Create the
ProjectDir/osgi-service/src/main/java/org/fusesource/example/service sub-directory. In this directory, use your favorite text editor to create the file, HelloWorldSvc.java, and add the code from Example 16.3, “The HelloWorldSvc Interface” to it.
Example 16.3. The HelloWorldSvc Interface
Writing the service class
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Create the
ProjectDir/osgi-service/src/main/java/org/fusesource/example/service/impl sub-directory. In this directory, use your favorite text editor to create the file, HelloWorldSvcImpl.java, and add the code from Example 16.4, “The HelloWorldSvcImpl Class” to it.
Example 16.4. The HelloWorldSvcImpl Class
Writing the blueprint file
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The blueprint configuration file is an XML file stored under the
OSGI-INF/blueprint directory on the class path. To add a blueprint file to your project, first create the following sub-directories:
ProjectDir/osgi-service/src/main/resources ProjectDir/osgi-service/src/main/resources/OSGI-INF ProjectDir/osgi-service/src/main/resources/OSGI-INF/blueprint
ProjectDir/osgi-service/src/main/resources
ProjectDir/osgi-service/src/main/resources/OSGI-INF
ProjectDir/osgi-service/src/main/resources/OSGI-INF/blueprint
Where the
src/main/resources is the standard Maven location for all JAR resources. Resource files under this directory will automatically be packaged in the root scope of the generated bundle JAR.
Example 16.5, “Blueprint File for Exporting a Service” shows a sample blueprint file that creates a
HelloWorldSvc bean, using the bean element, and then exports the bean as an OSGi service, using the service element.
Under the
ProjectDir/osgi-service/src/main/resources/OSGI-INF/blueprint directory, use your favorite text editor to create the file, config.xml, and add the XML code from Example 16.5, “Blueprint File for Exporting a Service”.
Example 16.5. Blueprint File for Exporting a Service
Running the service bundle
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To install and run the
osgi-service project, perform the following steps:
- Build the project—open a command prompt and change directory to
ProjectDir/osgi-service. Use Maven to build the demonstration by entering the following command:mvn install
mvn installCopy to Clipboard Copied! Toggle word wrap Toggle overflow If this command runs successfully, theProjectDir/osgi-service/targetdirectory should contain the bundle file,osgi-service-1.0-SNAPSHOT.jar. - Install and start the osgi-service bundle—at the Red Hat JBoss Fuse console, enter the following command:
JBossFuse:karaf@root> osgi:install -s file:ProjectDir/osgi-service/target/osgi-service-1.0-SNAPSHOT.jar
JBossFuse:karaf@root> osgi:install -s file:ProjectDir/osgi-service/target/osgi-service-1.0-SNAPSHOT.jarCopy to Clipboard Copied! Toggle word wrap Toggle overflow Where ProjectDir is the directory containing your Maven projects and the-sflag directs the container to start the bundle right away. For example, if your project directory isC:\Projectson a Windows machine, you would enter the following command:JBossFuse:karaf@root> osgi:install -s file:C:/Projects/osgi-service/target/osgi-service-1.0-SNAPSHOT.jar
JBossFuse:karaf@root> osgi:install -s file:C:/Projects/osgi-service/target/osgi-service-1.0-SNAPSHOT.jarCopy to Clipboard Copied! Toggle word wrap Toggle overflow NoteOn Windows machines, be careful how you format thefileURL—for details of the syntax understood by thefileURL handler, see Section A.1, “File URL Handler”. - Check that the service has been created—to check that the bundle has started successfully, enter the following Red Hat JBoss Fuse console command:
JBossFuse:karaf@root> osgi:list
JBossFuse:karaf@root> osgi:listCopy to Clipboard Copied! Toggle word wrap Toggle overflow Somewhere in this listing, you should see a line for theosgi-servicebundle, for example:[ 236] [Active ] [Created ] [ ] [ 60] osgi-service (1.0.0.SNAPSHOT)
[ 236] [Active ] [Created ] [ ] [ 60] osgi-service (1.0.0.SNAPSHOT)Copy to Clipboard Copied! Toggle word wrap Toggle overflow To check that the service is registered in the OSGi service registry, enter a console command like the following:JBossFuse:karaf@root> osgi:ls 236
JBossFuse:karaf@root> osgi:ls 236Copy to Clipboard Copied! Toggle word wrap Toggle overflow Where the argument to the preceding command is theosgi-servicebundle ID. You should see some output like the following at the console:Copy to Clipboard Copied! Toggle word wrap Toggle overflow
16.3. Accessing an OSGi Service
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Overview
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This section explains how to generate, build, and deploy a simple OSGi client in the OSGi container. The client finds the simple Hello World service in the OSGi registry and invokes the
sayHello() method on it.
Prerequisites
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In order to generate a project using the Maven Quickstart archetype, you must have the following prerequisites:
- Maven installation—Maven is a free, open source build tool from Apache. You can download the latest version from http://maven.apache.org/download.html (minimum is 2.0.9).
- Internet connection—whilst performing a build, Maven dynamically searches external repositories and downloads the required artifacts on the fly. In order for this to work, your build machine must be connected to the Internet.
Generating a Maven project
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The
maven-archetype-quickstart archetype creates a generic Maven project, which you can then customize for whatever purpose you like. To generate a Maven project with the coordinates, org.fusesource.example:osgi-client, enter the following command:
mvn archetype:create -DarchetypeArtifactId=maven-archetype-quickstart -DgroupId=org.fusesource.example -DartifactId=osgi-client
mvn archetype:create
-DarchetypeArtifactId=maven-archetype-quickstart
-DgroupId=org.fusesource.example
-DartifactId=osgi-client
The result of this command is a directory,
ProjectDir/osgi-client, containing the files for the generated project.
Note
Be careful not to choose a group ID for your artifact that clashes with the group ID of an existing product! This could lead to clashes between your project's packages and the packages from the existing product (because the group ID is typically used as the root of a project's Java package names).
Customizing the POM file
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You must customize the POM file in order to generate an OSGi bundle, as follows:
- Follow the POM customization steps described in Section 6.1, “Generating a Bundle Project”.
- Because the client uses the
HelloWorldSvcJava interface, which is defined in theosgi-servicebundle, it is necessary to add a Maven dependency on theosgi-servicebundle. Assuming that the Maven coordinates of theosgi-servicebundle areorg.fusesource.example:osgi-service:1.0-SNAPSHOT, you should add the following dependency to the client's POM file:Copy to Clipboard Copied! Toggle word wrap Toggle overflow
Writing the Blueprint file
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To add a blueprint file to your client project, first create the following sub-directories:
ProjectDir/osgi-client/src/main/resources ProjectDir/osgi-client/src/main/resources/OSGI-INF ProjectDir/osgi-client/src/main/resources/OSGI-INF/blueprint
ProjectDir/osgi-client/src/main/resources
ProjectDir/osgi-client/src/main/resources/OSGI-INF
ProjectDir/osgi-client/src/main/resources/OSGI-INF/blueprint
Under the
ProjectDir/osgi-client/src/main/resources/OSGI-INF/blueprint directory, use your favorite text editor to create the file, config.xml, and add the XML code from Example 16.6, “Blueprint File for Importing a Service”.
Example 16.6. Blueprint File for Importing a Service
Where the
reference element creates a reference manager that finds a service of HelloWorldSvc type in the OSGi registry. The bean element creates an instance of the Client class and injects the service reference as the bean property, helloWorldSvc. In addition, the init-method attribute specifies that the Client.init() method is called during the bean initialization phase (that is, after the service reference has been injected into the client bean).
Writing the client class
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Under the
ProjectDir/osgi-client/src/main/java/org/fusesource/example/client directory, use your favorite text editor to create the file, Client.java, and add the Java code from Example 16.7, “The Client Class”.
Example 16.7. The Client Class
The
Client class defines a getter and a setter method for the helloWorldSvc bean property, which enables it to receive the reference to the Hello World service by injection. The init() method is called during the bean initialization phase, after property injection, which means that it is normally possible to invoke the Hello World service within the scope of this method.
Running the client bundle
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To install and run the
osgi-client project, perform the following steps:
- Build the project—open a command prompt and change directory to
ProjectDir/osgi-client. Use Maven to build the demonstration by entering the following command:mvn install
mvn installCopy to Clipboard Copied! Toggle word wrap Toggle overflow If this command runs successfully, theProjectDir/osgi-client/targetdirectory should contain the bundle file,osgi-client-1.0-SNAPSHOT.jar. - Install and start the osgi-service bundle—at the Red Hat JBoss Fuse console, enter the following command:
JBossFuse:karaf@root> osgi:install -s file:ProjectDir/osgi-client/target/osgi-client-1.0-SNAPSHOT.jar
JBossFuse:karaf@root> osgi:install -s file:ProjectDir/osgi-client/target/osgi-client-1.0-SNAPSHOT.jarCopy to Clipboard Copied! Toggle word wrap Toggle overflow Where ProjectDir is the directory containing your Maven projects and the-sflag directs the container to start the bundle right away. For example, if your project directory isC:\Projectson a Windows machine, you would enter the following command:JBossFuse:karaf@root> osgi:install -s file:C:/Projects/osgi-client/target/osgi-client-1.0-SNAPSHOT.jar
JBossFuse:karaf@root> osgi:install -s file:C:/Projects/osgi-client/target/osgi-client-1.0-SNAPSHOT.jarCopy to Clipboard Copied! Toggle word wrap Toggle overflow NoteOn Windows machines, be careful how you format thefileURL—for details of the syntax understood by thefileURL handler, see Section A.1, “File URL Handler”. - Client output—f the client bundle is started successfully, you should immediately see output like the following in the console:
Bundle ID: 239 OSGi client started. Calling sayHello() Hello World!
Bundle ID: 239 OSGi client started. Calling sayHello() Hello World!Copy to Clipboard Copied! Toggle word wrap Toggle overflow
16.4. Integration with Apache Camel
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Overview
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Apache Camel provides a simple way to invoke OSGi services using the Bean language. This feature is automatically available whenever a Apache Camel application is deployed into an OSGi container and requires no special configuration.
Registry chaining
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When a Apache Camel route is deployed into the OSGi container, the
CamelContext automatically sets up a registry chain for resolving bean instances: the registry chain consists of the OSGi registry, followed by the blueprint (or Spring) registry. Now, if you try to reference a particular bean class or bean instance, the registry resolves the bean as follows:
- Look up the bean in the OSGi registry first. If a class name is specified, try to match this with the interface or class of an OSGi service.
- If no match is found in the OSGi registry, fall back on the blueprint registry (or the Spring registry, if you are using the Spring container).
Sample OSGi service interface
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Consider the OSGi service defined by the following Java interface, which defines the single method,
getGreeting():
package org.fusesource.example.hello.boston;
public interface HelloBoston {
public String getGreeting();
}
package org.fusesource.example.hello.boston;
public interface HelloBoston {
public String getGreeting();
}Sample service export
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When defining the bundle that implements the
HelloBoston OSGi service, you could use the following blueprint configuration to export the service:
Where it is assumed that the
HelloBoston interface is implemented by the HelloBostonImpl class (not shown).
Invoking the OSGi service from Java DSL
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After you have deployed the bundle containing the
HelloBoston OSGi service, you can invoke the service from a Apache Camel application using the Java DSL. In the Java DSL, you invoke the OSGi service through the Bean language, as follows:
from("timer:foo?period=5000")
.bean(org.fusesource.example.hello.boston.HelloBoston.class, "getGreeting")
.log("The message contains: ${body}")
from("timer:foo?period=5000")
.bean(org.fusesource.example.hello.boston.HelloBoston.class, "getGreeting")
.log("The message contains: ${body}")
In the
bean command, the first argument is the OSGi interface or class, which must match the interface exported from the OSGi service bundle. The second argument is the name of the bean method you want to invoke. For full details of the bean command syntax, see section "Bean Integration" in "Apache Camel Development Guide".
Note
When you use this approach, the OSGi service is implicitly imported. It is not necessary to import the OSGi service explicitly in this case.
Invoking the OSGi service from XML DSL
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In the XML DSL, you can also use the Bean language to invoke the
HelloBoston OSGi service, but the syntax is slightly different. In the XML DSL, you invoke the OSGi service through the Bean language, using the method element, as follows:
Note
When you use this approach, the OSGi service is implicitly imported. It is not necessary to import the OSGi service explicitly in this case.
Chapter 17. JMS Broker
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Abstract
Red Hat JBoss Fuse supports the deployment of JMS brokers. By default, it deploys an Apache ActiveMQ JMS broker. It includes all of the required bundles to deploy additional Apache ActiveMQ instances by deploying a new broker configuration.
17.1. Working with the Default Broker
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Abstract
Red Hat JBoss Fuse starts up with a message broker by default. You can use this broker as it is for your application, or you can update its configuration to suite the needs of your application.
Overview
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When you deploy a Red Hat JBoss Fuse instance, whether as a standalone container or as a part of a fabric, the default behavior is for a Apache ActiveMQ instance to be started in the container. The default broker creates an Openwire port that listens on port
61616. The broker remains installed in the container and activates whenever you restart the container.
Broker configuration
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The default broker's configuration is controlled by two files:
etc/activemq.xml—a standard Apache ActiveMQ configuration file that serves as a template for the default broker's configuration. It contains property place holders, specified using the syntax${propName}, that allow you to set the values of the actual property using the OSGi Admin service.etc/io.fabric8.mq.fabric.server-broker.cfg—the OSGi configuration file that specifies the values for the properties in the broker's template configuration file.
For details on how to edit the default broker's configuration see the JBoss A-MQ documentation.
Broker data
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The default broker's data is stored in
data/activemq. You can change this location using the config command to change the broker's data property as shown in Example 17.1, “Configuring the Default Broker's Data Directory”.
Example 17.1. Configuring the Default Broker's Data Directory
JBossFuse:karaf@root> config:edit io.fabric8.mq.fabric.server.3e3d0055-1c5f-40e3-987e-024c1fac1c3f JBossFuse:karaf@root> config:propset data dataStore JBossFuse:karaf@root> config:update
JBossFuse:karaf@root> config:edit io.fabric8.mq.fabric.server.3e3d0055-1c5f-40e3-987e-024c1fac1c3f
JBossFuse:karaf@root> config:propset data dataStore
JBossFuse:karaf@root> config:updateDisabling the default broker
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If you do not want to use the default broker, you can disable it by removing its OSGi configuration file. There are two procedures to follow, depending on whether a Karaf container has been started:
If no Karaf container has been started:
- Delete
FUSE_HOME/etc/io.fabric8.mq.fabric.server-broker.cfg.
If you have already started a Karaf container, use the following instructions whilst JBoss Fuse is running.
- From the JBoss Fuse command console, list the JBoss Fuse brokers:
activemq:listThe result should look like this:brokerName = amq
brokerName = amqCopy to Clipboard Copied! Toggle word wrap Toggle overflow - List the configuration PID files:
config:list | grep io.fabric8.mq.fabricThe result will look like this:Copy to Clipboard Copied! Toggle word wrap Toggle overflow - Delete the configuration PID files labeled
Pid:in the example above.config:delete io.fabric8.mq.fabric.server.cd4295e7-1db9-44b6-9118-69011a0f09a3 config:delete io.fabric8.mq.fabric.standalone.server.4de976b1-2fae-4391-97d9-3a08876e39ab
config:delete io.fabric8.mq.fabric.server.cd4295e7-1db9-44b6-9118-69011a0f09a3 config:delete io.fabric8.mq.fabric.standalone.server.4de976b1-2fae-4391-97d9-3a08876e39abCopy to Clipboard Copied! Toggle word wrap Toggle overflow Note that your files will have the same names as those shown above until the last numeric portion of the the file name, which is a system generated ID for the broker. Replace the filenames in the instructions with your actual filename. - List the JBoss Fuse brokers again:
activemq:listThe deleted broker will not appear. - To permanently delete the default broker:Stop the JBoss Fuse instance.Delete file
FUSE_HOME/etc/io.fabric8.mq.fabric.server-broker.cfg.Restart the JBoss Fuse instance and run theactivemq:listcommand. The deleted broker will not appear.
17.2. JMS Endpoints in a Router Application
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Overview
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The following example shows how you can integrate a JMS broker into a router application. The example generates messages using a timer; sends the messages through the
camel.timer queue in the JMS broker; and then writes the messages to a specific directory in the file system.
Prerequisites
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In order to run the sample router application, you need to have the
activemq-camel feature installed in the OSGi container. The activemq-camel component is needed for defining Apache ActiveMQ-based JMS endpoints in Apache Camel. This feature is not installed by default, so you must install it using the following console command:
JBossFuse:karaf@root> features:install activemq-camel
JBossFuse:karaf@root> features:install activemq-camel
You also need the
activemq feature, but this feature is normally available, because Red Hat JBoss Fuse installs it by default.
Tip
Most of the Apache Camel components are not installed by default. Whenever you are about to define an endpoint in a Apache Camel route, remember to check whether the corresponding component feature is installed. Apache Camel component features generally have the same name as the corresponding Apache Camel component artifact ID,
camel-ComponentName.
Router configuration
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Example 17.2, “Sample Route with JMS Endpoints” gives an example of a Apache Camel route defined using the Spring XML DSL. Messages generated by the timer endpoint are propagated through the JMS broker and then written out to the file system.
Example 17.2. Sample Route with JMS Endpoints
Camel activemq component
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In general, it is necessary to create a custom instance of the Apache Camel
activemq component, because you need to specify the connection details for connecting to the broker. The preceding example uses Spring syntax to instantiate the activemq bean which connects to the broker URL, tcp://localhost:61616. The broker URL must correspond to one of the transport connectors defined in the broker configuration file, deploy/test-broker.xml.
Sample routes
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Example 17.2, “Sample Route with JMS Endpoints” defines two routes, as follows:
- The first route uses a
timerendpoint to generate messages at four-second intervals. ThesetBodyelement places a dummy string in the body of the message (which would otherwise benull). The messages are then sent to thecamel.timerqueue on the broker (theactivemq:camel.timerendpoint).NoteTheactivemqscheme inactivemq:camel.timeris resolved by looking upactivemqin the bean registry, which resolves to the locally instantiated bean with ID,activemq. - The second route pulls messages off the
camel.timerqueue and then writes the messages to the specified directory,C:\temp\sandpit\timer, in the file system.
Steps to run the example
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To run the sample router application, perform the following steps:
- Using your favorite text editor, copy and paste the router configuration from Example 17.2, “Sample Route with JMS Endpoints” into a file called
camel-timer.xml.Edit the file endpoint in the second route, in order to change the target directory to a suitable location on your file system:<route> <from uri="activemq:camel.timer"/> <to uri="file:YourDirectoryHere!"/> </route><route> <from uri="activemq:camel.timer"/> <to uri="file:YourDirectoryHere!"/> </route>Copy to Clipboard Copied! Toggle word wrap Toggle overflow - Start up a local instance of the Red Hat JBoss Fuse runtime by entering the following at a command prompt:
./bin/fuse
./bin/fuseCopy to Clipboard Copied! Toggle word wrap Toggle overflow - Make sure the requisite features are installed in the OSGi container. To install the
activemq-camelfeature, enter the following command at the console:JBossFuse:karaf@root> features:install activemq-camel
JBossFuse:karaf@root> features:install activemq-camelCopy to Clipboard Copied! Toggle word wrap Toggle overflow To ensure that theactivemq-brokerfeature is not installed, enter the following command at the console:JBossFuse:karaf@root> features:uninstall activemq-broker
JBossFuse:karaf@root> features:uninstall activemq-brokerCopy to Clipboard Copied! Toggle word wrap Toggle overflow - Use one of the following alternatives to obtain a broker instance for this demonstration:
- Use the default broker—assuming you have not disabled the default broker, you can use it for this demonstration, because it is listening on the correct port, 61616.
- Create a new broker instance using the console—if you prefer not to use the default broker, you can disable it (as described in Section 17.1, “Working with the Default Broker”) and then create a new JMS broker instance by entering the following command at the console:
JBossFuse:karaf@root> activemq:create-broker --name test
JBossFuse:karaf@root> activemq:create-broker --name testCopy to Clipboard Copied! Toggle word wrap Toggle overflow After executing this command, you should see the broker configuration file,test-broker.xml, in theInstallDir/deploydirectory.
- Hot deploy the router configuration you created in step 1. Copy the
camel-timer.xmlfile into theInstallDir/deploydirectory. - Within a few seconds, you should start to see files appearing in the target directory (which is
C:\temp\sandpit\timer, by default). The file component automatically generates a unique filename for each message that it writes.It is also possible to monitor activity in the JMS broker by connecting to the Red Hat JBoss Fuse runtime's JMX port. To monitor the broker using JMX, perform the following steps:- To monitor the JBoss Fuse runtime, start a JConsole instance (a standard Java utility) by entering the following command:
jconsole
jconsoleCopy to Clipboard Copied! Toggle word wrap Toggle overflow - Initially, a JConsole: Connect to Agent dialog prompts you to connect to a JMX port. From the Local tab, select the
org.apache.felix.karaf.main.Bootstrapentry and click Connect. - In the main JConsole window, click on the MBeans tab and then drill down to
org.apache.activemq|test|Queuein the MBean tree (assuming thattestis the name of your broker). - Under the
Queuefolder, you should see thecamel.timerqueue. Click on thecamel.timerqueue to view statistics on the message throughput of this queue.
- To shut down the router application, delete the
camel-timer.xmlfile from theInstallDir/deploydirectory while the Karaf container is running.
Appendix A. URL Handlers
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Abstract
There are many contexts in Red Hat JBoss Fuse where you need to provide a URL to specify the location of a resource (for example, as the argument to a console command). In general, when specifying a URL, you can use any of the schemes supported by JBoss Fuse's built-in URL handlers. This appendix describes the syntax for all of the available URL handlers.
A.1. File URL Handler
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Syntax
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A file URL has the syntax,
file:PathName, where PathName is the relative or absolute pathname of a file that is available on the Classpath. The provided PathName is parsed by Java's built-in file URL handler. Hence, the PathName syntax is subject to the usual conventions of a Java pathname: in particular, on Windows, each backslash must either be escaped by another backslash or replaced by a forward slash.
Examples
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For example, consider the pathname,
C:\Projects\camel-bundle\target\foo-1.0-SNAPSHOT.jar, on Windows. The following example shows the correct alternatives for the file URL on Windows:
file:C:/Projects/camel-bundle/target/foo-1.0-SNAPSHOT.jar file:C:\\Projects\\camel-bundle\\target\\foo-1.0-SNAPSHOT.jar
file:C:/Projects/camel-bundle/target/foo-1.0-SNAPSHOT.jar
file:C:\\Projects\\camel-bundle\\target\\foo-1.0-SNAPSHOT.jar
The following example shows some incorrect alternatives for the file URL on Windows:
file:C:\Projects\camel-bundle\target\foo-1.0-SNAPSHOT.jar // WRONG! file://C:/Projects/camel-bundle/target/foo-1.0-SNAPSHOT.jar // WRONG! file://C:\\Projects\\camel-bundle\\target\\foo-1.0-SNAPSHOT.jar // WRONG!
file:C:\Projects\camel-bundle\target\foo-1.0-SNAPSHOT.jar // WRONG!
file://C:/Projects/camel-bundle/target/foo-1.0-SNAPSHOT.jar // WRONG!
file://C:\\Projects\\camel-bundle\\target\\foo-1.0-SNAPSHOT.jar // WRONG!A.2. HTTP URL Handler
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Syntax
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A HTTP URL has the standard syntax,
http:Host[:Port]/[Path][#AnchorName][?Query]. You can also specify a secure HTTP URL using the https scheme. The provided HTTP URL is parsed by Java's built-in HTTP URL handler, so the HTTP URL behaves in the normal way for a Java application.
A.3. Mvn URL Handler
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Overview
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If you use Maven to build your bundles or if you know that a particular bundle is available from a Maven repository, you can use the Mvn handler scheme to locate the bundle.
Note
To ensure that the Mvn URL handler can find local and remote Maven artifacts, you might find it necessary to customize the Mvn URL handler configuration. For details, see the section called “Configuring the Mvn URL handler”.
Syntax
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An Mvn URL has the following syntax:
mvn:[repositoryUrl!]groupId/artifactId[/[version][/[packaging][/[classifier]]]]
mvn:[repositoryUrl!]groupId/artifactId[/[version][/[packaging][/[classifier]]]]
Where repositoryUrl optionally specifies the URL of a Maven repository. The groupId, artifactId, version, packaging, and classifier are the standard Maven coordinates for locating Maven artifacts (see the section called “Maven coordinates”).
Omitting coordinates
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When specifying an Mvn URL, only the groupId and the artifactId coordinates are required. The following examples reference a Maven bundle with the groupId,
org.fusesource.example, and with the artifactId, bundle-demo:
mvn:org.fusesource.example/bundle-demo mvn:org.fusesource.example/bundle-demo/1.1
mvn:org.fusesource.example/bundle-demo
mvn:org.fusesource.example/bundle-demo/1.1
When the version is omitted, as in the first example, it defaults to
LATEST, which resolves to the latest version based on the available Maven metadata.
In order to specify a classifier value without specifying a packaging or a version value, it is permissible to leave gaps in the Mvn URL. Likewise, if you want to specify a packaging value without a version value. For example:
mvn:groupId/artifactId///classifier mvn:groupId/artifactId/version//classifier mvn:groupId/artifactId//packaging/classifier mvn:groupId/artifactId//packaging
mvn:groupId/artifactId///classifier
mvn:groupId/artifactId/version//classifier
mvn:groupId/artifactId//packaging/classifier
mvn:groupId/artifactId//packagingSpecifying a version range
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When specifying the version value in an Mvn URL, you can specify a version range (using standard Maven version range syntax) in place of a simple version number. You use square brackets—
[ and ]—to denote inclusive ranges and parentheses—( and )—to denote exclusive ranges. For example, the range, [1.0.4,2.0), matches any version, v, that satisfies 1.0.4 <= v < 2.0. You can use this version range in an Mvn URL as follows:
mvn:org.fusesource.example/bundle-demo/[1.0.4,2.0)
mvn:org.fusesource.example/bundle-demo/[1.0.4,2.0)Configuring the Mvn URL handler
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Before using Mvn URLs for the first time, you might need to customize the Mvn URL handler settings, as follows:
Check the Mvn URL settings
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The Mvn URL handler resolves a reference to a local Maven repository and maintains a list of remote Maven repositories. When resolving an Mvn URL, the handler searches first the local repository and then the remote repositories in order to locate the specified Maven artifiact. If there is a problem with resolving an Mvn URL, the first thing you should do is to check the handler settings to see which local repository and remote repositories it is using to resolve URLs.
To check the Mvn URL settings, enter the following commands at the console:
JBossFuse:karaf@root> config:edit org.ops4j.pax.url.mvn JBossFuse:karaf@root> config:proplist
JBossFuse:karaf@root> config:edit org.ops4j.pax.url.mvn
JBossFuse:karaf@root> config:proplist
The
config:edit command switches the focus of the config utility to the properties belonging to the org.ops4j.pax.url.mvn persistent ID. The config:proplist command outputs all of the property settings for the current persistent ID. With the focus on org.ops4j.pax.url.mvn, you should see a listing similar to the following:
Where the
localRepository setting shows the local repository location currently used by the handler and the repositories setting shows the remote repository list currently used by the handler.
Edit the configuration file
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To customize the property settings for the Mvn URL handler, edit the following configuration file:
InstallDir/etc/org.ops4j.pax.url.mvn.cfg
InstallDir/etc/org.ops4j.pax.url.mvn.cfg
The settings in this file enable you to specify explicitly the location of the local Maven repository, remove Maven repositories, Maven proxy server settings, and more. Please see the comments in the configuration file for more details about these settings.
Customize the location of the local repository
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In particular, if your local Maven repository is in a non-default location, you might find it necessary to configure it explicitly in order to access Maven artifacts that you build locally. In your
org.ops4j.pax.url.mvn.cfg configuration file, uncomment the org.ops4j.pax.url.mvn.localRepository property and set it to the location of your local Maven repository. For example:
Reference
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For more details about the
mvn URL syntax, see the original Pax URL Mvn Protocol documentation.
A.4. Wrap URL Handler
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Overview
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If you need to reference a JAR file that is not already packaged as a bundle, you can use the Wrap URL handler to convert it dynamically. The implementation of the Wrap URL handler is based on Peter Krien's open source Bnd utility.
Syntax
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A Wrap URL has the following syntax:
wrap:locationURL[,instructionsURL][$instructions]
wrap:locationURL[,instructionsURL][$instructions]
The locationURL can be any URL that locates a JAR (where the referenced JAR is not formatted as a bundle). The optional instructionsURL references a Bnd properties file that specifies how the bundle conversion is performed. The optional instructions is an ampersand,
&, delimited list of Bnd properties that specify how the bundle conversion is performed.
Default instructions
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In most cases, the default Bnd instructions are adequate for wrapping an API JAR file. By default, Wrap adds manifest headers to the JAR's
META-INF/Manifest.mf file as shown in Table A.1, “Default Instructions for Wrapping a JAR”.
| Manifest Header | Default Value |
|---|---|
Import-Package | *;resolution:=optional |
Export-Package | All packages from the wrapped JAR. |
Bundle-SymbolicName | The name of the JAR file, where any characters not in the set [a-zA-Z0-9_-] are replaced by underscore, _. |
Examples
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The following Wrap URL locates version 1.1 of the
commons-logging JAR in a Maven repository and converts it to an OSGi bundle using the default Bnd properties:
wrap:mvn:commons-logging/commons-logging/1.1
wrap:mvn:commons-logging/commons-logging/1.1
The following Wrap URL uses the Bnd properties from the file,
E:\Data\Examples\commons-logging-1.1.bnd:
wrap:mvn:commons-logging/commons-logging/1.1,file:E:/Data/Examples/commons-logging-1.1.bnd
wrap:mvn:commons-logging/commons-logging/1.1,file:E:/Data/Examples/commons-logging-1.1.bnd
The following Wrap URL specifies the
Bundle-SymbolicName property and the Bundle-Version property explicitly:
wrap:mvn:commons-logging/commons-logging/1.1$Bundle-SymbolicName=apache-comm-log&Bundle-Version=1.1
wrap:mvn:commons-logging/commons-logging/1.1$Bundle-SymbolicName=apache-comm-log&Bundle-Version=1.1
If the preceding URL is used as a command-line argument, it might be necessary to escape the dollar sign,
\$, to prevent it from being processed by the command line, as follows:
wrap:mvn:commons-logging/commons-logging/1.1\$Bundle-SymbolicName=apache-comm-log&Bundle-Version=1.1
wrap:mvn:commons-logging/commons-logging/1.1\$Bundle-SymbolicName=apache-comm-log&Bundle-Version=1.1Reference
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For more details about the
wrap URL handler, see the following references:
- The Bnd tool documentation, for more details about Bnd properties and Bnd instruction files.
- The original Pax URL Wrap Protocol documentation.
A.5. War URL Handler
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Overview
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If you need to deploy a WAR file in an OSGi container, you can automatically add the requisite manifest headers to the WAR file by prefixing the WAR URL with
war:, as described here.
Syntax
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A War URL is specified using either of the following syntaxes:
war:warURL warref:instructionsURL
war:warURL
warref:instructionsURL
The first syntax, using the
war scheme, specifies a WAR file that is converted into a bundle using the default instructions. The warURL can be any URL that locates a WAR file.
The second syntax, using the
warref scheme, specifies a Bnd properties file, instructionsURL, that contains the conversion instructions (including some instructions that are specific to this handler). In this syntax, the location of the referenced WAR file does not appear explicitly in the URL. The WAR file is specified instead by the (mandatory) WAR-URL property in the properties file.
WAR-specific properties/instructions
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Some of the properties in the
.bnd instructions file are specific to the War URL handler, as follows:
WAR-URL- (Mandatory) Specifies the location of the War file that is to be converted into a bundle.
Web-ContextPath- Specifies the piece of the URL path that is used to access this Web application, after it has been deployed inside the Web container.NoteEarlier versions of PAX Web used the property,
Webapp-Context, which is now deprecated.
Default instructions
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By default, the War URL handler adds manifest headers to the WAR's
META-INF/Manifest.mf file as shown in Table A.2, “Default Instructions for Wrapping a WAR File”.
| Manifest Header | Default Value |
|---|---|
Import-Package | javax.*,org.xml.*,org.w3c.* |
Export-Package | No packages are exported. |
Bundle-SymbolicName | The name of the WAR file, where any characters not in the set [a-zA-Z0-9_-\.] are replaced by period, .. |
Web-ContextPath | No default value. But the WAR extender will use the value of Bundle-SymbolicName by default. |
Bundle-ClassPath |
In addition to any class path entries specified explicitly, the following entries are added automatically:
|
Examples
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The following War URL locates version 1.4.7 of the
wicket-examples WAR in a Maven repository and converts it to an OSGi bundle using the default instructions:
war:mvn:org.apache.wicket/wicket-examples/1.4.7/war
war:mvn:org.apache.wicket/wicket-examples/1.4.7/war
The following Wrap URL specifies the
Web-ContextPath explicitly:
war:mvn:org.apache.wicket/wicket-examples/1.4.7/war?Web-ContextPath=wicket
war:mvn:org.apache.wicket/wicket-examples/1.4.7/war?Web-ContextPath=wicket
The following War URL converts the WAR file referenced by the
WAR-URL property in the wicket-examples-1.4.7.bnd file and then converts the WAR into an OSGi bundle using the other instructions in the .bnd file:
warref:file:E:/Data/Examples/wicket-examples-1.4.7.bnd
warref:file:E:/Data/Examples/wicket-examples-1.4.7.bndReference
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For more details about the
war URL syntax, see the original Pax URL War Protocol documentation.
Appendix B. OSGi Best Practices
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Abstract
The combination of Maven and the OSGi framework provides a sophisticated framework for building and deploying enterprise applications. In order to use this framework effectively, however, it is necessary to adopt certain conventions and best practices. The practices described in this appendix are intended to optimize the manageability and scalability of your OSGi applications.
B.1. OSGi Tooling
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Overview
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The following best practices are recommended for OSGi related tools and utilities:
Use the Maven bundle plug-in to generate the Manifest
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Even for a moderately sized bundle project, it is usually impractical to create and maintain a bundle Manifest by hand. The Maven bundle plug-in is the most effective tool for automating the generation of bundle Manifests in a Maven project. See Section B.2, “Building OSGi Bundles”.
Avoid using the OSGi API directly
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Avoid using the OSGi Java API directly. Prefer a higher level technology, for example: Blueprint (from the OSGi Compendium Specification), Spring-DM, Declarative Services (DS), iPojo, and so on.
Prefer Blueprint over Spring-DM
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The Blueprint container is now the preferred framework for instantiating, registering, and referencing OSGi services, because this container has now been adopted as an OSGi standard. This ensures greater portability for your OSGi service definitions in the future.
Spring Dynamic Modules (Spring-DM) provided much of the original impetus for the definition of the Blueprint standard, but should now be regarded as obsolescent. Using the Blueprint container does not prevent you from using the Spring framework: the latest version of Spring is compatible with Blueprint.
Use Apache Karaf features to group bundles together
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When an application is composed of a large number of bundles, it becomes essential to group bundles together in order to deploy them efficiently. Apache Karaf features is a mechanism that is designed just for this purpose. It is easy to use and supported by a variety of different tools. See Chapter 8, Deploying Features for details.
Use the OSGi Configuration Admin service
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The OSGi Configuration Admin service is the preferred mechanism for providing configuration properties to your application. This configuration mechanism enjoys better tooling support than other approaches. For example, in Red Hat JBoss Fuse the OSGi Configuration Admin service is supported in the following ways:
- Properties integrated with Spring XML files.
- Properties automatically read from configuration files,
etc/persistendId.cfg - Properties can be set in feature repositories.
Use PAX-Exam for testing
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In order for testing to be really effective, you should run at least some of your tests in an OSGi container. This requires you to start an OSGi container, configure its environment, install prerequisite bundles, and install the actual test. Performing these steps manually for every test would make testing prohibitively difficult and time-consuming. Pax-Exam solves this problem by providing a testing framework that is capable of automatically initializing an OSGi container before running tests in the container.
B.2. Building OSGi Bundles
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Overview
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The following best practices are recommended when building OSGi bundles using Maven:
Use package prefix as the bundle symbolic name
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Use your application's package prefix as the bundle symbolic name. For example, if all of your Java source code is located in sub-packages of
org.fusesource.fooProject, use org.fusesource.fooProject as the bundle symbolic name.
Artifact ID should be derived from the bundle symbolic name
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It makes sense to identify a Maven artifact with an OSGi bundle. To show this relationship as clearly as possible, you should use base the artifact ID on the bundle symbolic name. Two conventions are commonly used:
- The artifact ID is identical to the bundle symbolic name—this enables you to define the bundle symbolic name in terms of the artifact ID, using the following Maven bundle instruction:
<Bundle-SymbolicName>${project.artifactId}</Bundle-SymbolicName><Bundle-SymbolicName>${project.artifactId}</Bundle-SymbolicName>Copy to Clipboard Copied! Toggle word wrap Toggle overflow - The bundle symbolic name is composed of the group ID and the artifact ID, joined by a dot—this enables you to define the bundle symbolic name in terms of the group ID and the artifact ID, using the following Maven bundle instruction:
<Bundle-SymbolicName>${project.groupId}.${project.artifactId}</Bundle-SymbolicName><Bundle-SymbolicName>${project.groupId}.${project.artifactId}</Bundle-SymbolicName>Copy to Clipboard Copied! Toggle word wrap Toggle overflow
Note
Properties of the form
project.* can be used to reference the value of any element in the current POM. To construct the name of a POM property, take the XPath name of any POM element (for example, project/artifactId) and replace occurrences of / with the . character. Hence, ${project.artifactId} references the artifactId element from the current POM.
Always export packages with a version
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One of the key advantages of the OSGi framework is its ability to manage bundle versions and the possibility of deploying multiple versions of a bundle in the same container. In order to take advantage of this capability, however, it is essential that you associate a version with any packages that you export.
For example, you can configure the
maven-bundle-plugin plug-in to export packages with the current artifact version (given by the project.version property) as follows:
<Export-Package>
${project.artifactId}*;version=${project.version}
</Export-Package>
<Export-Package>
${project.artifactId}*;version=${project.version}
</Export-Package>
Notice how this example exploits the convention that packages use the artifact ID,
project.artifactId, as their package prefix. The combination of package prefix and wildcard, ${project.artifactId}*, enables you to reference all of the source code in your bundle.
Use naming convention for private packages
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If you define any private packages in your bundle (packages that you do not want to export), it is recommended that you identify these packages using a strict naming convention. For example, if your bundle includes implementation classes that you do not want to export, you should place these classes in packages prefixed by
${project.artifactId}.impl or ${project.artifactId}.internal.
Note
If you do not specify any
Export-Package instruction, the default behavior of the Maven bundle plug-in is to exclude any packages that contain a path segment equal to impl or internal.
To ensure that the private packages are not exported, you can add an entry of the form
!PackagePattern to the Maven bundle plug-in's export instructions. The effect of this entry is to exclude any matching packages. For example, to exclude any packages prefixed by ${project.artifactId}.impl, you could add the following instruction to the Maven bundle plug-in configuration:
<Export-Package>
!${project.artifactId}.impl.*,
${project.artifactId}*;version=${project.version}
</Export-Package>
<Export-Package>
!${project.artifactId}.impl.*,
${project.artifactId}*;version=${project.version}
</Export-Package>Note
The order of entries in the
Export-Package element is significant. The first match in the list determines whether a package is included or excluded. Hence, in order for exclusions to be effective, they should appear at the start of the list.
Import packages with version ranges
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In order to benefit from OSGi version management capabilities, it is important to restrict the range of acceptable versions for imported packages. You can use either of the following approaches:
- Manual version ranges—you can manually specify the version range for an imported package using the
versionqualifier, as shown in the following example:<Import-Package> org.springframework.*;version="[2.5,4)", org.apache.commons.logging.*;version="[1.1,2)", * </Import-Package>
<Import-Package> org.springframework.*;version="[2.5,4)", org.apache.commons.logging.*;version="[1.1,2)", * </Import-Package>Copy to Clipboard Copied! Toggle word wrap Toggle overflow Version ranges are specified using the standard OSGi version range syntax, where square brackets—that is,[and]—denote inclusive ranges and parentheses—that is,(and)—denote exclusive ranges. Hence the range,[2.5,4), means that the version,v, is restricted to the range,2.5 <= v < 4. Note the special case of a range written as a simple number—for example,version="2.5", which is equivalent to the range,[2.5,infinity). - Automatic version ranges—if packages are imported from a Maven dependency and if the dependency is packaged as an OSGi bundle, the Maven bundle plug-in automatically adds the version range to the import instructions.The default behavior is as follows. If your POM depends on a bundle that is identified as version 1.2.4.8, the generated manifest will import version 1.2 of the bundle's exported packages (that is, the imported version number is truncated to the first two parts, major and minor).It is also possible to customize how imported version ranges are generated from the bundle dependency. When setting the
versionproperty, you can use the${@}macro (which returns the original export version) and the${version}macro (which modifies a version number) to generate a version range. For example, consider the followingversionsettings:*;version="${@}"- If a particular package has export version
1.2.4.8, the generated import version resolves to1.2.4.8. *;version="${version;==;${@}}"- If a particular package has export version
1.2.4.8, the generated import version resolves to1.2. *;version="[${version;==;${@}},${version;=+;${@}})"- If a particular package has export version
1.2.4.8, the generated import version range resolves to[1.2,1.3). *;version="[${version;==;${@}},${version;+;${@}})"- If a particular package has export version
1.2.4.8, the generated import version range resolves to[1.2,2).
The middle part of the version macro—for example,==or=+—formats the returned version number. The equals sign,=, returns the corresponding version part unchanged; the plus sign,+, returns the corresponding version part plus one; and the minus sign,-, returns the corresponding version part minus one. For more details, consult the Bnd documentation for the version macro and the -versionpolicy option.
Note
In practice, you are likely to find that the majority of imported packages can be automatically versioned by Maven. It is, typically, only occasionally necessary to specify a version manually.
Avoid importing packages that you export
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Normally, it is not good practice to import the packages that you export (though there are exceptions to this rule). Here are some guidelines to follow:
- If the bundle is a pure library (providing interfaces and classes, but not instantiating any classes or OSGi services), do not import the packages that you export.
- If the bundle is a pure API (providing interfaces and abstract classes, but no implementation classes), do not import the packages that you export.
- If the bundle is a pure implementation (implementing and registering an OSGi service, but not providing any API), you do not need to export any packages at all.NoteThe registered OSGi service must be accessible through an API interface or class, but it is presumed that this API is provided in a separate API bundle. The implementation bundle therefore needs to import the corresponding API packages.
- A special case arises, if an implementation and its corresponding API are combined into the same bundle. In this case, the API packages must be listed amongst the export packages and amongst the import packages. This configuration is interpreted in a special way by the OSGi framework: it actually means that the API packages will either be exported or imported at run time (but not both).The reason for this special configuration is that, in a complex OSGi application, it is possible that an API package might be provided by more than one bundle. But you do not want multiple copies of an API to be exported into OSGi, because that can lead to technical problems like class cast exceptions. When a package is listed both in the exports and in the imports, the OSGi resolver proceeds as follows:
- First of all, the resolver checks whether the package has already been exported from another bundle. If so, the resolver imports the package, but does not export it.
- Otherwise, the resolver uses the local API package and exports this package, but it does not import the package.
Assuming you want to avoid importing the packages that you export, there are two alternative approaches you can take, as follows:
- (Recommended) The most effective way of suppressing the import of exported packages is to append the
-noimport:=truesetting to package patterns in theExport-Packageinstruction. For example:<Export-Package> ${project.artifactId}*;version=${project.version};-noimport:=true </Export-Package><Export-Package> ${project.artifactId}*;version=${project.version};-noimport:=true </Export-Package>Copy to Clipboard Copied! Toggle word wrap Toggle overflow The marked packages are now not imported, irrespective of what is contained in theImport-Packageinstruction. - An alternative way of avoiding the import is to add one or more package exclusions to the Maven bundle plug-in's
Import-Packageelement (this was the only possibility in earlier versions of the Maven bundle plug-in). For example, the followingImport-Packageelement instructs the Maven bundle plug-in to exclude all packages prefixed by the artifact ID,${project.artifactId}:Copy to Clipboard Copied! Toggle word wrap Toggle overflow
Use optional imports with caution
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When an imported package is specified with optional resolution, this allows the bundle to be resolved without resolving the optional package. This affects the resolution order of the bundles which, in turn, can affect the runtime behavior. You should therefore be careful with optional imports, in case they have some unintended side effects.
A package is optional when it appears in the
Import-Package manifest header with the resolution:="optional" setting appended to it. For example, the following example shows an Import-Package instruction for the Maven bundle plug-in that specifies an optional import:
<Import-Package> org.springframework.*;version="[2.5,4)", org.apache.commons.logging.*;version="[1.1,2)";resolution:="optional", * </Import-Package>
<Import-Package>
org.springframework.*;version="[2.5,4)",
org.apache.commons.logging.*;version="[1.1,2)";resolution:="optional",
*
</Import-Package>Avoid using the Require-Bundle header
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Avoid using the
Require-Bundle header, if possible. The trouble with using the Require-Bundle header is that it forces the OSGi resolver to use packages from the specified bundle. Importing at the granularity of packages, on the other hand, allows the resolver to be more flexible, because there are fewer constraints: if a package is already available and resolved from another bundle, the resolver could use that package instead.
B.3. Sample POM File
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POM file
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Example B.1, “Sample POM File Illustrating Best Practices” shows a sample POM that illustrates the best practices for building an OSGi bundle using Maven.
Example B.1. Sample POM File Illustrating Best Practices
Index
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B
- broker.xml, Broker configuration
- Bundle-Name, Setting a bundle's name
- Bundle-SymbolicName, Setting a bundle's symbolic name
- Bundle-Version, Setting a bundle's version
- bundles, OSGi Bundles
- exporting packages, Specifying exported packages
- importing packages, Specifying imported packages
- lifecycle states, Bundle lifecycle states
- name, Setting a bundle's name
- private packages, Specifying private packages
- symbolic name, Setting a bundle's symbolic name
- version, Setting a bundle's version
C
- class loading, Class Loading in OSGi
- Conditional Permission Admin service, OSGi framework services
- Configuration Admin service, OSGi Compendium services
- console, Red Hat JBoss Fuse
D
- default broker
- configuration, Broker configuration
- data directory, Broker data
- disabling, Disabling the default broker
- default repositories, Adding a default Maven repository
E
- execution environment, OSGi architecture
- Export-Package, Specifying exported packages
I
- Import-Package, Specifying imported packages
- io.fabric8.mq.fabric.server-default.cfg, Broker configuration
J
- JBoss Fuse, Red Hat JBoss Fuse
- console, Red Hat JBoss Fuse
L
- lifecycle layer, OSGi architecture
- lifecycle states, Bundle lifecycle states
M
- Maven
- local repository, Customizing the location of the local Maven repository
- remote repositories, Adding a remote Maven repository
- module layer, OSGi architecture
O
- org.ops4j.pax.url.mvn.localRepository.localRepository, Customizing the location of the local Maven repository
- org.ops4j.pax.url.mvn.localRepository.settings, Customizing the location of the local Maven repository
- org.ops4j.pax.url.mvn.repositories, Adding a remote Maven repository, Adding a default Maven repository
- OSGi Compendium services, OSGi Compendium services
- Configuration Admin service, OSGi Compendium services
- OSGi framework, OSGi Framework
- bundles, OSGi architecture
- execution environment, OSGi architecture
- lifecycle layer, OSGi architecture
- module layer, OSGi architecture
- security layer, OSGi architecture
- service layer, OSGi architecture
- OSGi framework services, OSGi framework services
- Conditional Permission Admin service, OSGi framework services
- Package Admin service, OSGi framework services
- Permission Admin service, OSGi framework services
- Start Level service, OSGi framework services
- URL Handlers service, OSGi framework services
- OSGi service registry, OSGi service registry
- OSGi services, OSGi Services
- service invocation model, Service invocation model
- service registry, OSGi service registry
P
- Package Admin service, OSGi framework services
- Permission Admin service, OSGi framework services
- Private-Package, Specifying private packages
R
- remote repositories, Adding a remote Maven repository
- repositories
- default, Adding a default Maven repository
- remote, Adding a remote Maven repository
S
- security layer, OSGi architecture
- service layer, OSGi architecture
- Start Level service, OSGi framework services
U
- URL Handlers service, OSGi framework services
Legal Notice
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The text of and illustrations in this document are licensed by Red Hat under a Creative Commons Attribution–Share Alike 3.0 Unported license ("CC-BY-SA"). An explanation of CC-BY-SA is available at http://creativecommons.org/licenses/by-sa/3.0/. In accordance with CC-BY-SA, if you distribute this document or an adaptation of it, you must provide the URL for the original version.
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