Build and Version Numbering for Java Projects (ant, cvs, hudson)

For several of my projects I capture the subversion revision number, time, user who ran the build, and some system information, stuff them into a .properties file that gets included in the application jar, and read that jar at runtime.

The ant code looks like this:

<!-- software revision number --><property name="version" value="1.23"/><target name="buildinfo">    <tstamp>        <format property="builtat" pattern="MM/dd/yyyy hh:mm aa" timezone="America/New_York"/>    </tstamp>            <exec executable="svnversion" outputproperty="svnversion"/>    <exec executable="whoami" outputproperty="whoami"/>    <exec executable="uname" outputproperty="buildsystem"><arg value="-a"/></exec>    <propertyfile file="path/to/project.properties"        comment="This file is automatically generated - DO NOT EDIT">                <entry key="buildtime" value="${builtat}"/>        <entry key="build" value="${svnversion}"/>        <entry key="builder" value="${whoami}"/>        <entry key="version" value="${version}"/>        <entry key="system" value="${buildsystem}"/>    </propertyfile></target>

It's simple to extend this to include whatever information you might want to add.

Your build.xml

...<property name="version" value="1.0"/>...<target name="jar" depends="compile">    <buildnumber file="build.num"/>    <manifest file="MANIFEST.MF">        ...        <attribute name="Main-Class" value="MyClass"/>        <attribute name="Implementation-Version" value="${version}.${build.number}"/>        ...    </manifest></target>...

Your java code

String ver = MyClass.class.getPackage().getImplementationVersion();

• Build numbers should be associated with a continuous integration server like hudson. Use different jobs for different branches/teams/distributions.
• To keep the version number in the final build, I would recommend just using maven for build system. It will create a .properties file archived into the final .jar/.war/.whatever-ar on META-INF/maven/<project group>/<project id>/pom.properties. The .properties file will contain the version property.
• Since I am recommending maven, I would urge you to check out the release plugin to prepare the release on source repository and keep the versions on sync.