Visualizer, Part 3: Poor Man's PDE Build

This is the third in my series (Part 1, Part 2) of posts about Visualizer. In this post I'll be talking about how to create a simplified PDE build.

As I mentioned in the previous post, Visualizer is built on OSGi. My preferred development environment for doing any Java development, but especially OSGi development, is Eclipse because of its wonderful JDT and PDE tooling. The PDE team has created an awesome environment for developing and managing OSGi bundles. However, one of the requirements that I had for Visualizer was that anyone could download the source code and build it, regardless of their IDE or environment preferences. PDE includes the ability to perform a headless build, but I didn't really want to expect the user to download Eclipse or to include a stripped down version of Eclipse in the Visualizer distribution just so the user could build it from the commandline. So I set out to create a "Poor Man's PDE Build" using just Ant.

Actually building the plugins with Ant is relatively simple. This short Ant file will build the plugin:

<?xml version="1.0" encoding="UTF-8"?>
<project default="build-plugin">
    <property name="src.dir" value="src"/>
    <property name="classes.dir" value="bin"/>
    <property file="META-INF/MANIFEST.MF"/>
    <property file="build.properties"/>
    
    <path id="classpath">
        <fileset dir="${dist.dir}">
            <include name="*.jar"/>
        </fileset>
        <fileset file="${osgi.framework}"/>
        <pathelement path="${java.class.path}"/>
    </path>
    
    <target name="init">
        <mkdir dir="${classes.dir}"/>
    </target>
    
    <target name="compile" depends="init">
        <echo message="Compiling the ${Bundle-SymbolicName} plugin"/>
        <javac srcdir="${src.dir}" destdir="${classes.dir}" classpathref="classpath" debug="true"/>
    </target>
    
    <target name="copy-resources">
        <echo message="Copying resources"/>
        <copy todir="${classes.dir}">
            <fileset dir="." includes="${bin.includes}"/>
        </copy>
    </target>
    
    <target name="build-plugin" depends="compile, copy-resources">
        <jar jarfile="${dist.dir}/${Bundle-SymbolicName}_${Bundle-Version}.jar" basedir="${classes.dir}" manifest="META-INF/MANIFEST.MF"/>
    </target>
    
    <target name="clean">
        <delete includeemptydirs="true">
            <fileset dir="${classes.dir}" includes="**/*"/>
        </delete>
    </target>
</project>

As you can see here, there really isn't much to the actual build. The best part is we can use the META-INF/MANIFEST.MF and build.properties created when we're working in PDE to control the build.

For a single bundle with no dependencies, this effectively duplicates the PDE build process. The difficulties comes in when you start having dependencies. If you use the headless PDE build, it will sort out all the dependencies for you and build your bundles in the proper order.

Implementing proper dependency resolution seemed awfully complicated, especially since PDE build already implements it. Fortunately, Visualizer doesn't require complicated dependency resolution because I've structured the bundles in a logical order. There are three levels of bundles: "core" which implement the main functionality, "ui" which implement the user interface to the core bundles, and "application" bundles that build on both the core and ui bundles.

Armed with this knowledge, we can structure a three stage build process where we first build all of the core bundles then all of the ui bundles and then all of the application bundles. To accomplish this, we have a master build.xml that calls out to the template build-plugin.xml file listed above using a subant task.

<target name="build-framework" depends="init">
    <!-- build org.andrill.visualizer, org.andrill.visualizer.services* -->
    <subant target="build-plugin" genericantfile="build-plugin.xml" failonerror="false">
        <property name="dist.dir" value="../${build.dir}"/>
        <property name="osgi.framework" value="../framework.jar"/>
        <dirset dir=".">
            <include name="org.andrill.visualizer"/>
            <include name="org.andrill.visualizer.services*"/>
        </dirset>
    </subant>
</target>

Here you can see we build first the org.andrill.visualizer bundle and then all of the org.andrill.visualizer.services bundles. As we build each bundle, we copy the bundled JAR file to our dist.dir. Each time a bundle is built, it creates its classpath from all of the JARs in dist.dar. So even though there are dependencies among bundles, we are progressively fulfilling those dependencies by collecting the built bundles in dist.dir.

Once all of the "core" bundles are built, we can kick off the build of the ui bundles:

<target name="build-ui" depends="build-framework">
    <!-- build org.andrill.visualizer.ui* -->
    <subant target="build-plugin" genericantfile="build-plugin.xml" failonerror="false">
        <property name="dist.dir" value="../${build.dir}"/>
        <property name="osgi.framework" value="../framework.jar"/>
        <dirset dir=".">
            <include name="org.andrill.visualizer.ui*"/>
        </dirset>
    </subant>
</target>

Finally we can build all of the "application" bundles by excluding everything we've already built:

<target name="build-apps" depends="build-framework, build-ui">
    <subant target="build-plugin" genericantfile="build-plugin.xml" failonerror="false">
        <property name="dist.dir" value="../${build.dir}"/>
        <property name="osgi.framework" value="../framework.jar"/>
        <dirset dir=".">
            <include name="*.*"/>
            <exclude name="org.andrill.visualizer"/>
            <exclude name="org.andrill.visualizer.services*"/>
            <exclude name="org.andrill.visualizer.ui*"/>
            <exclude name="${build.dir}"/>
            <exclude name="${dist.dir}"/>
        </dirset>
    </subant>
</target>

You can check out the full build file at: build.xml and build-plugin.xml.

It's not nearly as neat as just kicking off a PDE build and letting it do all of the hard work of figuring out the dependencies for you. However, I'm rather fond of my approach because it keeps me honest. If I create a new bundle and it starts breaking the build, then I know I need to go back and make sure I've thought through the dependencies and am not trying to mix "core" code with "ui" code and such. And there's no need to bundle Eclipse with the source to build the thing.