どのJarにクラスが入ってるか探す

public class ClassFinder {

    public static void main(String[] args) throws Exception {
	String className = System.getProperty("className");
        System.out.println("Going to search " + className);

        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        System.out.println("Context ClassLoader is " + loader);

        String path = className.replace('.', '/').concat(".class");

	Enumeration<URL> enu = ((URLClassLoader)loader).findResources(path);
        while (enu.hasMoreElements()) {
            System.out.println(enu.nextElement());
        }
    }
}

ant から使うとクラスパスが柔軟に設定できていいと思う。

...
  <path id="build.classpath">
    <fileset dir="lib">
      <include name="*.jar"/>
    </fileset>
    <fileset dir="${jboss.home}/client">
      <include name="*.jar"/>
    </fileset>

    <fileset dir="${jboss.home}/server/${server.name}/lib">
      <include name="**/*.jar"/>
    </fileset>
  </path>

  <target name="run" depends="compile">
    <java classname="test.ClassFinder" fork="true">
      <sysproperty key="className" value="${className}"/>
      <classpath refid="build.classpath"/>
    </java>
  </target>
...
[tkobayas@tkobayas JarSearch]$ ant run -DclassName=javax.ejb.Stateless
Buildfile: build.xml

compile:

run:
     [java] Going to search javax.ejb.Stateless
     [java] Context ClassLoader is sun.misc.Launcher$AppClassLoader@17182c1
     [java] jar:file:/home/tkobayas/usr/local/jboss-eap-4.3.0.GA_CP07/jboss-as/client/jboss-ejb3x.jar!/javax/ejb/Stateless.class
     [java] jar:file:/home/tkobayas/usr/local/jboss-eap-4.3.0.GA_CP07/jboss-as/server/default/lib/jboss-ejb3x.jar!/javax/ejb/Stateless.class

BUILD SUCCESSFUL
Total time: 2 seconds