1.2. Preparing to use Maven
Overview
This section gives a brief overview of how to prepare Maven for building Red Hat JBoss A-MQ projects and introduces the concept of Maven coordinates, which are used to locate Maven artifacts.
Prerequisites
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 A-MQ repository
In order to access artifacts from the Red Hat JBoss A-MQ 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 A-MQ 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 A-MQ repository as shown in bold text in Example 1.1, “Adding the Red Hat JBoss A-MQ Repositories to Maven”.
Example 1.1. Adding the Red Hat JBoss A-MQ Repositories to Maven
<settings>
<profiles>
<profile>
<id>my-profile</id>
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<repositories>
<repository>
<id>fusesource</id>
<url>http://repo.fusesource.com/nexus/content/groups/public/</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
<releases>
<enabled>true</enabled>
</releases>
</repository> <repository>
<id>fusesource.snapshot</id>
<url>http://repo.fusesource.com/nexus/content/groups/public-snapshots/</url>
<snapshots>
<enabled>true</enabled>
</snapshots>
<releases>
<enabled>false</enabled>
</releases>
</repository>
<repository>
<id>apache-public</id>
<url>https://repository.apache.org/content/groups/public/</url>
<snapshots>
<enabled>true</enabled>
</snapshots>
<releases>
<enabled>true</enabled>
</releases>
</repository>
<!-- The rebuilt artifacts for the client aren't available in hosted
maven repository. There is a file-based repo that can optionally
be installed using the -maven-repo RPM files, creating a repo
at /usr/share/java/maven-repo -->
<repository>
<id>amq-client-repo</id>
<url>file:///usr/share/java/maven-repo</url>
<releases>
<enabled>true</enabled>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
</repositories>
</profile>
</profiles>
...
</settings>
The preceding example also shows repository element for the following repositories:
fusesource-snapshotrepository—if you want to experiment with building your application using an Red Hat JBoss A-MQ snapshot kit, you can include this repository.apache-publicrepository—you might not always need this repository, but it is often useful to include it, because JBoss A-MQ depends on many of the artifacts from Apache.
Artifacts
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
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
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:
<project ... > ... <groupId>org.fusesource.example</groupId> <artifactId>bundle-demo</artifactId> <packaging>bundle</packaging> <version>1.0-SNAPSHOT</version> ... </project>
For example, to define a dependency on the preceding artifact, you could add the following
dependency element to a POM:
<project ... >
...
<dependencies>
<dependency>
<groupId>org.fusesource.example</groupId>
<artifactId>bundle-demo</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
</dependencies>
...
</project>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.
