Understanding JVMs

CICS® provides the support you need to run a Java™ program in a z/OS Java Virtual Machine (JVM) executing under the control of a CICS region. CICS support for JVMs allows you to run CICS application programs written in the Java language and compiled to bytecode by any standard Java compiler. You can find information about Java on the z/OS platform at http://www.ibm.com/servers/eserver/zseries/software/java/

CICS TS 3.1 supports the JVM provided by the IBM® Software Developer Kit for z/OS®, Java 2 Technology Edition, Version 1.4.2 .
Note: There are two versions of the IBM Software Developer Kit for z/OS, Java 2 Technology Edition Version 1.4, a 31-bit and a 64-bit version. CICS TS 3.1 supports only the 31-bit version, which must be at the 1.4.2 level.
This JVM features persistent reusable JVM technology and includes several optimizations designed for the execution of CICS transactions. These optimizations are:

The structure of a JVM tells you what you need to know about the structure of a JVM in order to use JVMs with CICS.

CICS performs the following management tasks relating to JVMs:

Setting up Java support tells you how to set up and use JVMs in your CICS system.

Java programs that ran under CICS Transaction Server for z/OS, Version 2 Release 2 or CICS Transaction Server for z/OS, Version 2 Release 3 can also run under CICS Transaction Server for z/OS, Version 3 Release 1. CICS Transaction Server for z/OS, Version 2 supported the JVM created by the IBM Developer Kit for OS/390 Java 2 Technology Edition Version 1.3.1s, which also featured the persistent reusable JVM technology. However, the older type of JVM that was introduced in CICS Transaction Server for OS/390®, Version 1 Release 3, which was not reusable, is no longer supported. Any Java programs that ran under CICS Transaction Server for OS/390, Version 1 Release 3 must be migrated to Java 2 to run under the JVM provided by the IBM Software Developer Kit for z/OS, Java 2 Technology Edition, Version 1.4.2. Removal of support for CICS Transaction Server for OS/390, Version 1 Release 3 JVMs has more information about this.