ANT eclipse headless build - java.lang.NoClassDefFoundError

I am trying to make a headless build that requires eclipse specific tasks.

For launching the ant buildfile, I use the following command. I do it this way because I believe it allows me to run eclipse tasks that previously complained that they needed a workspace to run in. If this is incorrect/if there is a better way, please inform me.

My batch script:

    java -jar %EQUINOX_LAUNCHER_JAR% -application org.eclipse.ant.core.antRunner -buildfile %ANT_SCRIPT_JAR% -data %WORKSPACE_PATH%

Inside my ant buildfile, I need to define a task:

<taskdef name="myTask" classname="path.to.class.with.execute"><classpath><pathelement location="path\to\dependency.jar"/></classpath></taskdef>

When running

<myTask/>

I get

java.lang.NoClassDefFoundError: path/to/class/that/I/tried/to/import

Solution

Classes which your task’s code uses must be in the classpath. One option is to add them explicitly to the classpath when defining the task:

<taskdef name="myTask" classname="path.to.class.with.execute">
    <classpath>
        <pathelement location="path/to/dependency.jar"/>
        <pathelement location="path/to/transitive-dependency.jar"/>
        <pathelement location="path/to/other-transitive-dependency.jar"/>
    </classpath>
</taskdef>

If all the .jar files are in the same directory tree, you can shorten it to:

<taskdef name="myTask" classname="path.to.class.with.execute">
    <classpath>
        <fileset dir="path/to/dir" includes="**/*.jar"/>
    </classpath>
</taskdef>

One other possibility is to add a Class-Path attribute to the manifest of the .jar which contains the task class. The attribute’s value is a space separated list of relative URLs, with their implied base being the .jar file where the manifest resides. For example:

Class-Path: transitive-dependency.jar utils/other-transitive-dependency.jar

If you’re building the task .jar itself in Ant, you can specify the Class-Path attribute in Ant’s jar task:

<jar destfile="task.jar">
    <fileset dir="classes"/>
    <manifest>
        <attribute name="Class-Path"
            value="transitive-dependency.jar utils/other-transitive-dependency.jar"/>
    </manifest>
</jar>