Architecture Manual 
This documentation provides an overview of the architecture of the SAP Web Application Server for Java. It describes the setup of a J2EE cluster and the components involved.
Also, it describes the system architecture of the SAP J2EE Engine.
Integration
You can operate the SAP J2EE Engine solely for J2EE applications or together with the ABAP Engine in the SAP Web AS.
The integrated scenario is described in the documentation section SAP Web Application Server with ABAP and J2EE.
This architecture overview provides an introduction to and background information for administration and development of J2EE applications with the SAP Web AS.
The SAP Library for J2EE technology contains the following additional sections:
Technical Operations Manual for the SAP J2EE Engine
In the section Overview of the Available Manuals you will find a summary of the contents, as well as the target audience the manuals are intended for.
Features
The Architecture Manual is divided into the following sections:
SAP J2EE Engine System Architecture
Introduction to SAP NetWeaver Developer Studio (this documentation is also in the Development Manual)
Java Persistence (You can also find this documentation in the Development Manual)