SAP Web Application Server with ABAP and J2EE 

Uses

You can install the SAP Web Application Server in various ways:

·         J2EE only (see J2EE Cluster Architecture)

·         ABAP + J2EE add-in

For installation details see Installation Information.

The following describes the integrated version with ABAP and J2EE.

ABAP and J2EE Minimal Installation

The architecture of this type of system (with one instance) looks like:

This system provides the following functions:

·        Operation using SAPGUI

Users log on to the dispatcher and work processes perform the users’ tasks.

·        Processing Web requests.

Web requests are received by an Internet Communication Manager (ICM). These HTTP(S) requests may be designated for the Internet Communication Framework (ICF), that is, processed in an ABAP work process (for example, BSP Applications), or they may be J2EE requests, designated for the J2EE Engine.

With the help of the URL the ICM decides where it will forward the request to (see below).

Installation with Several SAP Web AS Instances

The following graphic shows an SAP System with three instances:

As the system should offer ABAP and J2EE, each instance must contain an Internet Communication Manager (ICM) that can receive Web requests.

Each of these integrated instances of the SAP Web AS contains the (ABAP) dispatcher and its work processes, which can process the ABAP programs, as well as the J2EE dispatcher and its server processes, to which it distributes the incoming J2EE requests.

One of the instances must provide must be installed as the (ABAP) central instance, that is, offer the enqueue service. Alternatively, you can work with the Standalone Enqueue Server, and without a central instance.

Of course, you do not have to use the Web Client to log on to an SAP System – you can also log on from the SAP GUI menu.  The message server is used for this as well as for transmitting requests in the ABAP world.

The J2EE cluster requires a special instance, the Central Services, for managing locks and transmitting messages and data.

Finally, all the applications and data for ABAP and J2EE each have a database.

Integration

To operate the SAP J2EE Engine, the following services must be active in the HTTP service tree (Transaction SICF):

·        /sap/public/icman: The ICM uses this service to forward requests to the J2EE server.

·        /sap/public/icf_info supplies the SAP Web Dispatcher with details of logon groups, server load, etc.

These services must be activated so that the SAP Web dispatcher and the ICM can forward the request correctly.

If these services are not active, you have to activate them in transaction SICF, as described here.

Functions

Distributing HTTP Requests Using the SAP Web Dispatcher

The SAP Web Dispatcher is the central access point from the Internet into the SAP System. The SAP Web dispatcher has to decide to which SAP Web AS it will send each incoming request. The procedure for this is described in section Server Selection and Load Balancing Using the SAP Web Dispatcher.

Processing HTTP(S) Requests Using the ICM

For each incoming HTTP request, the ICM must decide whether it should forward the request for processing to the ABAP engine (the ICF) or to the SAP J2EE engine.

This decision is made using the URL prefix. The ICM uses the same procedure as the SAP Web Dispatcher.

Communication Between the ICM and J2EE Dispatcher

A separate protocol is used for the communication between the ICM and J2EE Dispatcher. This protocol is described in Communication Between ICM and J2EE Engine.

Caching in the ICM

You can also use the Internet Server Cache with the J2EE server, in order to store HTTP responses (such as HTML pages or images). The next time, the request can be retrieved directly from the cache.