Detecting Cycles using JDepend and Ant

Package dependency cycles are bad, mmkay? However, it’s amazing how easy it is for cycles to accidentally appear, especially among teams of developers who may not be aware of the pitfalls. Ideally, I would like the automated build to break if a cycle appears, ensuring that the problem can be fixed up before it gets out of hand.

JDepend already reports if cycles are present between packages, but it isn’t as easy as it could be to cause the build to break. One suggestion is to write a JUnit test that runs JDepend separately, and fails if a cycle is found (see the JDepend documentation). Although possible, I don’t think it is as elegant as it could be, because:

• I have to get the path to the compiled code into the unit test, either by hard coding the path, or possibly passing it in as a parameter somehow. This is tight coupling between the unit test and the place from which it runs.
• I have to invoke JDepend twice: once to check for cycles, and again to generate the HTML report.

I think that an Ant script is a much better place for this functionality: it already has all the path information, all it needs is a way to find out if there are any cycles. If so, it can fail the build if appropriate. Unfortunately, the current JDepend Ant task doesn’t provide a way to find out. Until now, that is! I’ve just completed a couple of patches: one to JDepend itself, and another to the JDepend Ant task. My patch added an extra attribute to the <jdepend> element called “cyclesdetectedproperty”. This will set a property if JDepend detected a cycle. I expect that this could be used in a manner similar to this:

<target name="report-jdepend" depends="compile"
       description="Creates a package dependency report">
   <mkdir dir="${java-report.jdepend-data-dir}"/>
   <jdepend outputfile="${java-report.jdepend-data-dir}/jdepend.xml"
            format="xml"
            cyclesdetectedproperty="jdepend-cycles-found">
       <exclude name="java.*"/>
       <exclude name="javax.*"/>
       <classespath>
           <pathelement location="${java-build.classes-dir}"/>
       </classespath>
   </jdepend>

   <mkdir dir="${java-report.jdepend-dir}"/>
   <xslt basedir="${java-report.jdepend-data-dir}"
          destdir="${java-report.jdepend-dir}"
          includes="jdepend.xml"
          style="${ant.home}/etc/jdepend.xsl"/>

   <fail if="jdepend-cycles-found">Cyclical package dependencies found</fail>
</target>

I haven’t released these patches yet, but I will soon be adding it to the Ant Script Library. All going well, I’ll try and get the patches rolled back into the JDepend and Ant code bases. Let me know if you’re interested in seeing it earlier.

Update:

I just spotted the verifydesign task in AntContrib, which actually does what I would like, and more. Pretty neat, but I’d still prefer that I could fail the build from JDepend, as it is a much simpler task to configure.