Appendix A. Using the Maven OSGi Tooling

A Maven project for building an OSGi bundle can be a simple single level project. It does not require any sub-projects. However, it does require that you do the following:

A project that constructs an OSGi bundle can be a single level project. It only requires that you have a top-level POM file and a src folder. As in all Maven projects, you place all Java source code in the src/java folder, and you place any non-Java resources in the src/resources folder.

Non-Java resources include Spring configuration files, JBI endpoint configuration files, and WSDL contracts.

Before you can use the bundle plug-in you must add a dependency on Apache Felix. After you add the dependency, you can add the bundle plug-in to the plug-in portion of the POM.

Example A.1, “Adding an OSGi bundle plug-in to a POM” shows the POM entries required to add the bundle plug-in to your project.

...
<dependencies>
  <dependency>
    <groupId>org.apache.felix</groupId>
    <artifactId>org.osgi.core</artifactId>
    <version>1.0.0</version>
  </dependency>
...
</dependencies>
...
<build>
  <plugins>
    <plugin>
      <groupId>org.apache.felix</groupId>
      <artifactId>maven-bundle-plugin</artifactId>
      <configuration>
        <instructions>
          <Bundle-SymbolicName>${pom.artifactId}</Bundle-SymbolicName>
          <Import-Package>*,org.apache.camel.osgi</Import-Package>
          <Private-Package>org.apache.servicemix.examples.camel</Private-Package>
        </instructions>
      </configuration>
    </plugin>
  </plugins>
</build>
...

The entries in Example A.1, “Adding an OSGi bundle plug-in to a POM” do the following:

Adds the dependency on Apache Felix

Adds the bundle plug-in to your project

Configures the plug-in to use the project’s artifact ID as the bundle’s symbolic name

Configures the plug-in to include all Java packages imported by the bundled classes; also imports the org.apache.camel.osgi package

Configures the plug-in to bundle the listed class, but not to include them in the list of exported packages

For more information on configuring the bundle plug-in, see Section A.3, “Configuring the Bundle Plug-In”.

To have Maven use the bundle plug-in, instruct it to package the results of the project as a bundle. Do this by setting the POM file’s packaging element to bundle.

There are several Maven archetypes available to generate a project that is preconfigured to use the bundle plug-in:

The Spring OSGi archetype creates a generic project for building an OSGi project using Spring DM, as shown:

org.springframework.osgi/spring-bundle-osgi-archetype/1.1.2

You invoke the archetype using the following command:

mvn archetype:generate -DarchetypeGroupId=org.springframework.osgi -DarchetypeArtifactId=spring-osgi-bundle-archetype -DarchetypeVersion=1.1.2 -DgroupId=groupId -DartifactId=artifactId -Dversion=version

The Apache CXF code-first archetype creates a project for building a service from Java, as shown:

org.apache.servicemix.tooling/servicemix-osgi-cxf-code-first-archetype/2010.02.0-fuse-02-00

You invoke the archetype using the following command:

mvn archetype:generate -DarchetypeGroupId=org.apache.servicemix.tooling -DarchetypeArtifactId=servicemix-osgi-cxf-code-first-archetype -DarchetypeVersion=2010.02.0-fuse-02-00 -DgroupId=groupId -DartifactId=artifactId -Dversion=version

The Apache CXF wsdl-first archetype creates a project for creating a service from WSDL, as shown:

org.apache.servicemix.tooling/servicemix-osgi-cxf-wsdl-first-archetype/2010.02.0-fuse-02-00

You invoke the archetype using the following command:

mvn archetype:generate -DarchetypeGroupId=org.apache.servicemix.tooling -DarchetypeArtifactId=servicemix-osgi-cxf-wsdl-first-archetype -DarchetypeVersion=2010.02.0-fuse-02-00 -DgroupId=groupId -DartifactId=artifactId -Dversion=version

The Apache Camel archetype creates a project for building a route that is deployed into JBoss Fuse, as shown:

org.apache.servicemix.tooling/servicemix-osgi-camel-archetype/2010.02.0-fuse-02-00

You invoke the archetype using the following command:

mvn archetype:generate -DarchetypeGroupId=org.apache.servicemix.tooling -DarchetypeArtifactId=servicemix-osgi-camel-archetype -DarchetypeVersion=2010.02.0-fuse-02-00 -DgroupId=groupId -DartifactId=artifactId -Dversion=version

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.

Some of the commonly used configuration properties are:

By default, the bundle plug-in sets the value for the Bundle-SymbolicName property to groupId + "." + artifactId, with the following exceptions:

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 A.2, “Setting a bundle’s symbolic name”.

<plugin>
  <groupId>org.apache.felix</groupId>
  <artifactId>maven-bundle-plugin</artifactId>
  <configuration>
   <instructions>
     <Bundle-SymbolicName>${project.artifactId}</Bundle-SymbolicName>
     ...
    </instructions>
  </configuration>
</plugin>

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 A.3, “Setting a bundle’s name”.

<plugin>
  <groupId>org.apache.felix</groupId>
  <artifactId>maven-bundle-plugin</artifactId>
  <configuration>
   <instructions>
     <Bundle-Name>JoeFred</Bundle-Name>
     ...
    </instructions>
  </configuration>
</plugin>

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 A.4, “Setting a bundle’s version”.

<plugin>
  <groupId>org.apache.felix</groupId>
  <artifactId>maven-bundle-plugin</artifactId>
  <configuration>
   <instructions>
     <Bundle-Version>1.0.3.1</Bundle-Version>
     ...
    </instructions>
  </configuration>
</plugin>

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 default package, ., and any packages containing .impl or .internal.

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.*

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.

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.

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 A.5, “Including a private package in a bundle” shows the configuration for including a private package in a bundle

<plugin>
  <groupId>org.apache.felix</groupId>
  <artifactId>maven-bundle-plugin</artifactId>
  <configuration>
   <instructions>
     <Private-Package>org.apache.cxf.wsdlFirst.impl</Private-Package>
     ...
    </instructions>
  </configuration>
</plugin>

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.

Example A.6, “Specifying the packages imported by a bundle” shows the configuration for specifying the packages imported by a bundle

<plugin>
  <groupId>org.apache.felix</groupId>
  <artifactId>maven-bundle-plugin</artifactId>
  <configuration>
   <instructions>
     <Import-Package>javax.jws, javax.wsdl, org.apache.cxf.bus, org.apache.cxf.bus.spring, org.apache.cxf.bus.resource, org.apache.cxf.configuration.spring, org.apache.cxf.resource, org.springframework.beans.factory.config, * </Import-Package>
     ...
   </instructions>
  </configuration>
</plugin>

For more information on configuring a bundle plug-in, see: