How to monitor and tuning JVM

  Experts,

      in my customer,  there are 35000 users for internet expense, and 8000 users for forms (gl, fa, po, inv, ar). EBS version is 11.5.10.2, database is 10.2.0.3, and JDK is 1.4.2.  Platform is AIX 5.3L,  and resources as following:

      ------------------------------------------------------------

      Node            CPU                  Mem

      apps node1   15C                   48g

      apps node2   15C                   48g

      db     rac1     15C                   54g

      db     rac2     15C                   54g

      ------------------------------------------------------------

     when OIE concurrent user more than 300, java session consumes more than 50% CPU, and outputs many javacore files because of JVM outmemory. How to monitor the JVM, and what is JVM doing, and how to tuning?

thanks

Jason