NullPointerException in SessionData.removeAttribute, getServletContext

Question

I am trying to setup Session replication on BEA10 installed on my non multihomed windows machine.
          I have added two managed servers (MS1, MS2) to the cluster (MYCLUSTER) and have set the cluster MYCLUSTER as the target for my web application.
          Information about my setup is as follows -
          1. I have set my machine to have static IP
          2. For load balancing, I have installed weblogic.servlet.proxy.HttpClusterServlet on third managed server (MS3). This third server is not part of the cluster, MYCLUSTER
          3. Load balancing is working fine because when I hit the URL of the app the request goes in round-robin to each server in the cluster.
          This I have verified from the logs of both the servers (MS1, MS2).
          4. When I hit one of the servers (say MS1) and login into the application the app starts working fine and I am able to navigate through different pages.
          Now the problem is that when I shutdown the MS1 which has responded to the current session and then try to navigate further in the application, I get following exceptions in the log file of the MS2.
          Point worth noting is that some part of the session has got replicated to the MS2 because I remain logged-in into the application when I try to send request to the app which is now being served by MS2.
          The User Info is available in session in the second server and also appears on the page.
          5. I have set <persistent-store-type>replicated</persistent-store-type> under session-descriptor in weblogic.xml
          6. I have deployed app as exploded WAR and have set <page-check-seconds>0</page-check-seconds> for jsp hot deployment.
          ####<Aug 30, 2007 10:53:51 AM MST> <Error> <HTTP> <VCHADD745> <Server9080> <[ACTIVE] ExecuteThread: '10' for queue: 'weblogic.kernel.Default (self-tuning)'> <<WLS Kernel>> <> <> <1188496431495> <BEA-101020> <[weblogic.servlet.internal.WebAppServletContext@2226390 - appName: 'mywebapp', name: 'mywebapp.war', context-path: '/mywebapp'] Servlet failed with Exception
          java.lang.NullPointerException
               at weblogic.servlet.internal.session.SessionData.removeAttribute(SessionData.java:627)
               at weblogic.servlet.internal.session.SessionData.removeAttribute(SessionData.java:586)
               at weblogic.servlet.internal.session.ReplicatedSessionData.removeAttribute(ReplicatedSessionData.java:523)
               at com.mypackage.SomeSessionContext.clear(SomeSessionContext.java:893)
          java.lang.NullPointerException
               at weblogic.servlet.internal.session.SessionData.getServletContext(SessionData.java:233)
               at com.mypackage.SomeSessionContext.getApplicationBean(SomeSessionContext.java:199)                    Code at line 893 SomeSessionContext.java
          this.session.removeAttribute(element);                    Code at 199 in SomeSessionContext.java
          ServletContext servletContext = this.session.getServletContext();                    Please help me resolve the issue.

Answer 1

I was able to resolve the issue. Actually we were keeping handle to session object in another object which was being stored in session. Since session object is not serializable its reference in the replicated object was null. This was causing the NPE when on the replicated server code was trying to get something from null session refrence.