Chapter 17. Pax CDI and OSGi Services

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).

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:

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)"

A bundle that includes the preceding Require-Capability bundle header effectively becomes a bean bundle (a CDI enabled bundle).

To enable Pax CDI in Apache Karaf, perform the following steps:

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.

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)"

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:

<project ...>
  ...
  <build>
    <plugins>
      ...
      <plugin>
        <groupId>org.apache.felix</groupId>
        <artifactId>maven-bundle-plugin</artifactId>
        <extensions>true</extensions>
        <configuration>
          <instructions>
            <Bundle-SymbolicName>${project.groupId}.${project.artifactId}</Bundle-SymbolicName>
            <Import-Package>*</Import-Package>
            <Require-Capability>
              osgi.extender; filter:="(osgi.extender=pax.cdi)",
              org.ops4j.pax.cdi.extension; filter:="(extension=pax-cdi-extension)"
            </Require-Capability>
          </instructions>
        </configuration>
      </plugin>
      ...
    </plugins>
  </build>
  ...
</project>

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:

<project ...>
  ...
  <dependencies>
    ...
    <!-- CDI API -->
    <dependency>
        <groupId>org.ops4j.pax.cdi</groupId>
        <artifactId>pax-cdi-api</artifactId>
        <version>1.0.0.RC1</version>
    </dependency>
    ...
  </dependencies>
  ...
</project>