Sharing Session Data Across WARS

Although sharing session data across WARS is a Servlet 2.4 spec violation, and a potential security issue, there is a semi-reasonable business case for it:

A large application is broken up into multiple WARS, so that new functionality can be pushed out in a more modularized fashion.

While there is a more elegant way to handle this via JBossCache, it is possible to get JBoss 4.0.2 to share session data across WARs. I used http://www.fwd.at/tomcat/sharing-session-data-howto.html as a reference for sharing session data across WARs.

WARNING - I was not able to get this to work in Tomcat 5.5.7 or Tomcat 5.5.9 standalone. Sharing of session data across WARS is a violation of the Servlet 2.4 spec and this workaround should be considered a last resort!

In a nutshell, this is what I did:

• Created a simple struts app/configuration for my test JSPs and Actions.

• Write a method that stores session data in a "shared" context.

      private synchronized void storeDataInContext(ServletContext context, String sessionid, Object data) {          

         //load the shared_userroles from the context
         Hashtable shareddata = (Hashtable)context.getAttribute("shared_data");

         // if not yet available, create a new one
         if (shareddata==null) {
            shareddata = new Hashtable();
         }

         // store the userroles of the current session
         shareddata.put(sessionid, data);

         // store the shareddata back into the Context
         context.setAttribute("shared_data", shareddata);
         System.out.println("I SET THE DATA OBJ TO: " + data);
      }

• Write method that gets data from the shared context.

      private Object getDataFromContext(ServletContext context,     String sessionid) {

         // get the Context containing the shared session data
      ServletContext ssocontext = context.getContext("/wars-session-share");

      Object data = null;

      // read the shareddata
      Hashtable shareddata = (Hashtable) ssocontext.getAttribute("shared_data");
         if (shareddata != null) {
          // get the right object using the ssosessionid
          data = shareddata.get(sessionid);
         }

      return data;
      }

• Make sure jbossweb-tomcat55.sar\META-INF\jboss-service.xml has UseJBossWebLoader="true". Otherwise, you will get a ClassCastException.

I've attached the source, so you can try this approach. I've included a simple ant build.xml script that'll compile/deploy the code to jboss or tomcat. I don't know why it doesn't work in standalone tomcat, but I'm pretty sure the issue is configuration related.