J2EE Instance 

Definition

A J2EE instance is a unit in the J2EE 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 J2EE 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 J2EE instance contains at least one Server Process.

Normally it comprises one J2EE Dispatcher and several server processes.

A J2EE instance is started and stopped by the J2EE Startup and Control Framework.

Integration

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

Example

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

The J2EE dispatcher receives the request, selects a server process for the processing and establishes the connection from the client to the server.