Appendix A. Preparing to use Maven

This section gives a brief overview of how to prepare Maven for building Red Hat Fuse projects and introduces the concept of Maven coordinates, which are used to locate Maven artifacts.

A.1. Preparing to set up Maven

Maven is a free, open source, build tool from Apache. Typically, you use Maven to build Fuse applications.

Procedure

  1. Download the latest version of Maven from the Maven download page.

  2. Ensure that your system is connected to the Internet.

    While building a project, the default behavior is that Maven searches external repositories and downloads the required artifacts. Maven looks for repositories that are accessible over the Internet.

    You can change this behavior so that Maven searches only repositories that are on a local network. That is, Maven can run in an offline mode. In offline mode, Maven looks for artifacts in its local repository. See Section A.3, “Using local Maven repositories”.

A.2. Adding Red Hat repositories to Maven

To access artifacts that are in Red Hat Maven repositories, you need to add those repositories to Maven’s settings.xml file. Maven looks for the settings.xml file in the .m2 directory of the user’s home directory. If there is not a user specified settings.xml file, Maven uses the system-level settings.xml file at M2_HOME/conf/settings.xml.

Prerequisite

You know the location of the settings.xml file in which you want to add the Red Hat repositories.

Procedure

In the settings.xml file, add repository elements for the Red Hat repositories as shown in this example: 

<?xml version="1.0"?>
<settings>

  <profiles>
    <profile>
      <id>extra-repos</id>
      <activation>
        <activeByDefault>true</activeByDefault>
      </activation>
      <repositories>
       <repository>
            <id>redhat-ga-repository</id>
            <url>https://maven.repository.redhat.com/ga</url>
            <releases>
                <enabled>true</enabled>
            </releases>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
        <repository>
            <id>redhat-ea-repository</id>
            <url>https://maven.repository.redhat.com/earlyaccess/all</url>
            <releases>
                <enabled>true</enabled>
            </releases>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
        <repository>
          <id>jboss-public</id>
          <name>JBoss Public Repository Group</name>
          <url>https://repository.jboss.org/nexus/content/groups/public/</url>
        </repository>
      </repositories>
      <pluginRepositories>
        <pluginRepository>
            <id>redhat-ga-repository</id>
            <url>https://maven.repository.redhat.com/ga</url>
            <releases>
                <enabled>true</enabled>
            </releases>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </pluginRepository>
        <pluginRepository>
            <id>redhat-ea-repository</id>
            <url>https://maven.repository.redhat.com/earlyaccess/all</url>
            <releases>
                <enabled>true</enabled>
            </releases>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </pluginRepository>
        <pluginRepository>
          <id>jboss-public</id>
          <name>JBoss Public Repository Group</name>
          <url>https://repository.jboss.org/nexus/content/groups/public</url>
        </pluginRepository>
      </pluginRepositories>
    </profile>
  </profiles>

  <activeProfiles>
    <activeProfile>extra-repos</activeProfile>
  </activeProfiles>

</settings>

A.3. Using local Maven repositories

If you are running the Apache Karaf container without an Internet connection, and you need to deploy an application that has dependencies that are not available offline, you can use the Maven dependency plug-in to download the application’s dependencies into a Maven offline repository. You can then distribute this customized Maven offline repository to machines that do not have an Internet connection.

Procedure

  1. In the project directory that contains the pom.xml file, download a repository for a Maven project by running a command such as the following: 

    mvn org.apache.maven.plugins:maven-dependency-plugin:3.1.0:go-offline -Dmaven.repo.local=/tmp/my-project

    In this example, Maven dependencies and plug-ins that are required to build the project are downloaded to the /tmp/my-project directory.

  2. Distribute this customized Maven offline repository internally to any machines that do not have an Internet connection.

A.4. About Maven artifacts and coordinates

In the Maven build system, the basic building block is an artifact. After a build, the output of an artifact is typically an archive, such as a JAR or WAR file.

A key aspect of Maven is the ability to locate artifacts and manage the dependencies between them. A Maven coordinate is a set of values that identifies the location of a particular artifact. A basic coordinate has three values in the following form:

groupId:artifactId:version

Sometimes Maven augments a basic coordinate with a packaging value or with both a packaging value and a classifier value. A Maven coordinate can have any one of the following forms: 

groupId:artifactId:version
groupId:artifactId:packaging:version
groupId:artifactId:packaging:classifier:version

Here are descriptions of the values:

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 of 1.0-SNAPSHOT is 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 is jar.
classifier
Enables you to distinguish between artifacts that were built from the same POM, but have different content.

Elements in an artifact’s POM file define the artifact’s group ID, artifact ID, packaging, and version, as shown here: 

<project ... >
  ...
  <groupId>org.fusesource.example</groupId>
  <artifactId>bundle-demo</artifactId>
  <packaging>bundle</packaging>
  <version>1.0-SNAPSHOT</version>
  ...
</project>

To define a dependency on the preceding artifact, you would add the following dependency element to a POM file: 

<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.