5 Replies Latest reply on Apr 5, 2002 8:26 PM by Adrian Brock

    How do I access MBean service from EJB Bean Impl?

    Won Cho Newbie

      There's RMIConnector instance registered to JNDI service w/ lookup name "jmx:<machine name>:rmi". Using that instance, I can invoke any MBean operations. It works fine from remote client where it can instanciate RMIClientConnectorImpl. (internally, it looks up for the RMIConnector through JNDI.)

      Now... I want to do the same thing from EJB bean impl. But, I'm getting ClassNotFound error for the RMIConnector class type where RMIConnector is from lib/ext/jboss.jar.

      I believe that there's unique classloader assigned to each ejb.jar, war.jar, or ear.jar. Though, I don't know where it's parent classloader comes from. (Maybe from MLet to load bootstrap services?) Since jboss.jar is loaded by ClassPathExtension MBean (internally, it uses MLet), jboss.jar is loaded from different classloader.

      How can I enable the EJB bean to acess the class from jboss.jar?

      or... is there any other way EJB bean can use MBean service? BTW, I'm using jboss 2.4.4

      Your help is greately appreciated.

        • 1. Re: How do I access MBean service from EJB Bean Impl?
          Won Cho Newbie

          Great. It works now.

          MBeanServer server = (MBeanServer) MBeanServerFactory.findMBeanServer(null).iterator().next();

          Then, invoke through the server works fine.
          The MBeanServerFactory came from lib/jmxri.jar, and somehow it can access jars from lib/ext. But, from EJB, it cannot access the jars from lib/ext. How is that possible?

          The parent of the ClassLoader of EJB can load the jars from lib, and the parent of the ClassLoader of lib can load jars from lib/ext????

          • 2. Re: How do I access MBean service from EJB Bean Impl?
            Adrian Brock Master

            I'm not sure I understand the problem.
            What is the error you see?

            There are three levels of classloader

            lib - created by the manifest of run.jar
            lib/ext - created by jboss.conf
            ejb - the thread context class loader

            Regards,
            Adrian

            • 3. Re: How do I access MBean service from EJB Bean Impl?
              Won Cho Newbie

              Hello Adrian.
              I think I solved that funky problem.

              From run.jar of the jboss bin directory, it has this manifest attribute:
              Class-Path: ../lib/jmxri.jar ../conf/ ../client/jboss-client.jar ../lib/jaas.jar ../lib/jdbc2_0-stdext.jar ../lib/jboss-jaas.jar ../lib/jaxp.jar

              So, the default classloader loads the jmxri.jar.
              The parent of MLet classloader is the default classloader.

              This MLet classloader loads all jars from jboss where ./ is the lib/ext directory.
              <!-- Place the config directory in the classpath -->




              So, those jars from lib/ext ask the default classloader before MLet classloader. Because the MLet's parent is the default classloader, jmxri.jar can access the classes from the lib/ext jars.

              The EJB's classloader must not be MLet. Its parent classloader must be the default classloader.
              So, EJB class can access those classes from jmxri.jar.

              To summarize the point, the classes loaded by the parent classloader can use the classes loaded by its child classloader. And, vice-versa.
              But, the classes loaded by one child classloader cannot use the class loaded by another child classload although they have same parent classloader.

              • 4. Re: How do I access MBean service from EJB Bean Impl?
                Adrian Brock Master

                Yes,

                This is standard java classloader behaviour.

                JBoss3.0 changes this rule with the UnifiedClassLoaders.
                All child classloaders are available from other childs
                of a global parent.

                It isn't standard java classloading, but it simplifies
                the packaging and allows other performance enhancements.

                Regards,
                Adrian

                • 5. Re: How do I access MBean service from EJB Bean Impl?
                  Adrian Brock Master

                  Actually, as a further clarification

                  Under standard java, a parent cannot access a child's
                  classes during dynamic classloading, unless
                  the child's classloader is set as the thread's classloader.

                  Regards,
                  Adrian