The bundle-manifest task allows you to create a JAR manifest with the necessary OSGi headers for the bundle to be created.

<project name="example.freespace" default="all">

  [..]
  <!-- Build manifest from bundle descriptor and add additional entries -->
  <bundle-manifest file="${build.classes.dir}/META-INF/MANIFEST.MF"
        classes="${build.classes.dir}"
        descriptor="${basedir}/bundle.xml">
    <attribute name="Bundle-Version" value="${version}"/>
    <attribute name="Bundle-Vendor" value="${implementation.vendor}"/>
    <attribute name="Bundle-DocURL" value="${implementation.url}"/>
    <attribute name="Implementation-Title"
        value="${Name} (${subproject-name})"/>
    <attribute name="Implementation-Version" value="${version}"/>
    <attribute name="Implementation-Vendor"
        value="${implementation.vendor}"/>
    <attribute name="Implementation-URL"
        value="${implementation.url}"/>
  </bundle-manifest>
  
  <!-- Now build the actual bundle. -->
  <jar jarfile="${build.dir}/${subproject-name}.jar"
        filesetmanifest="merge" manifestencoding="UTF-8">
    <fileset dir="${build.classes.dir}"/>
    <metainf dir="${project-root.dir}" includes="LICENSE.txt,NOTICE.txt"/>
  </jar>
  [..]
</project>

The example above shows a typical use of the bundle-manifest task. As you can see, the first step is to generate the manifest which is written to /META-INF/MANIFEST.MF (in the directory where you place the compiled classes). The jar task can then merge that generated manifest into the final manifest that will be found in the JAR file (see filesetmanifest="merge").

The file attribute specifies the manifest file to be written.

The descriptor attribute specifies the bundle descriptor for the bundle.

The classes attribute specifies the directory containing the compiled Java classes to be analyzed to determine all necessary imports.

Additionally, you can add a nested path element (See Ant's path-like structures) as a child of bundle-manifest to specify additional JAR files that will be assumed to be embedded in the bundle (under /META-INF/lib/). These embedded JARs will also be scanned for external dependencies. You are, however, responsible for copying these JARs to the right place in the classes directory so they end up in the bundle/JAR and are found at runtime.

Finally, you can provide any number of header attributes just like is possible in Ant's manifest or jar tasks. It is recommended to provide at least the Bundle-Version header so the bundle's version number is applied to all exports.