Why does Ant say “NoClassDefFound” when my JAR is on the classpath?

Question

I am using Java 1.6, Eclipse, and Ant.

The following is my target for creating a jar file and running it:

Answer 1

You've set the compile classpath but the App.jar does not include your libs (only the classes you compiled) or a manifest classpath.

You'll need to do the following:

<target name="jar">
    <mkdir dir="${jar.dir}" />
    <manifestclasspath property="manifest.classpath"
                       jarfile="${jar.dir}/App.jar">
      <classpath refid="classpath" />
    </manifestclasspath>
    <jar destfile="${jar.dir}/App.jar" basedir="${classes.dir}">
        <manifest>
            <attribute name="Main-Class" value="main.App" />
            <attribute name="Class-Path" value="${manifest.classpath}" />.
        </manifest>
    </jar>
</target>

See also ant manifestclasspath task