Java Instance 

Definition

A Java instance is a unit in the SAP Web Java cluster, which can be started, stopped, and monitored separately. It runs on a physical server; but it is also possible to run several instances on one server. An instance is identified by the system ID (SID) and the instance number.

Central Services are a special example of a Java instance.

Another special instance is the one that installed the SDM (Software Deployment Manager). This one usually runs with the database and Central Services on the same machine and is then indicated as the central instance.

Structure

A Java instance contains at least one Server Process.

Normally it comprises one Java Dispatcher and several server processes.

A Java instance is started and stopped by the Java Startup and Control Framework.

Integration

There could also be Java instances in mixed ABAP/J2EE systems, as well as in Java-only systems. See SAP Web Application Server with ABAP and Java.

Example

An HTTP request that wants to execute a servlet, runs the following layers in the J2EE engine.

The Java dispatcher receives the request, selects a server process for the processing and establishes the connection from the client to the server.