CICS® provides the tools and runtime environment to develop and run Java™ enterprise applications in a Java Virtual Machine (JVM) that is under the control of a CICS region. Java applications can interact with CICS services and applications written in other languages.
Java on z/OS®
provides comprehensive support for running Java applications.
CICS uses the IBM® 64-bit SDK for z/OS, Java Technology Edition, Version 7, 
Version 7
Release 1
, or Version 8. Any of the three versions can be used, but all
JVM servers running in a CICS region must use the same
version. Check the Java releases that are supported by this CICS Transaction server release at 
CICS
Transaction Server for z/OS 5.1 detailed system requirements. The SDK contains a Java Runtime Environment that supports the full set of Java APIs and a set of development tools. To encourage the
adoption of Java on z/OS, a special processor is available in certain z Systems™ hardware. This processor is
called the IBM zEnterprise® Application Assist Processor (zAAP) and can
provide additional processor capacity to run eligible Java
workloads at a reduced cost. CICS can exploit this capability
in its Java workloads. You can find more information about Java on the z/OS platform
and download the 64-bit version of the SDK at http://www.ibm.com/servers/eserver/zseries/software/java/.
CICS provides an Eclipse-based tool and the JVM server runtime environment for Java applications:
- CICS Explorer® SDK
The CICS Explorer SDK is a freely available download for Eclipse-based Integrated Development Environments (IDEs). The SDK provides support for developing and deploying applications that comply with the OSGi Service Platform specification. The OSGi Service Platform provides a mechanism for developing applications using a component model and deploying those applications into a framework as OSGi bundles. An OSGi bundle is the unit of deployment for an application component and contains version control information, dependencies, and application code. The main benefit of OSGi is that you can create applications from reusable components that are accessed only though well-defined interfaces called OSGi services. You can also manage the life cycle and dependencies of Java applications in a granular way.
The CICS Explorer SDK supports developing Java applications for any supported release of CICS. The SDK includes the Java CICS (JCICS) library of classes to access CICS services and examples to get started with developing applications for CICS. You can also use the tool to convert existing Java applications to OSGi.
- JVM server
The JVM server is the strategic runtime environment for Java applications in CICS. A JVM server can handle many concurrent requests from different Java applications in a single JVM. Use of a JVM server reduces the number of JVMs that are required to run Java applications in a CICS region. To use a JVM server, Java applications must be threadsafe and must comply with the OSGi specification. JVM server provides the following benefits:
- Eligible Java workloads can run on zAAP processors, reducing the cost of transactions.
- Different types of work such as threadsafe Java programs and web services, can run in a JVM server.
- Application life cycle can be managed in the OSGi framework, without restarting the JVM server.
- Java applications that are packaged using OSGi can be
ported more easily between CICS and other
platforms.Note: OSGi applications in CICS can be installed in a Liberty JVM server but cannot use any of the Liberty services or features as they are not supported.
