Welcome to the Application Server space. This is the SDN WIKI starting point for topics around the Application Server.
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The SAP NetWeaver Application Server is the last development of what we used to refer to as the SAP Web Application Server. It is the technological foundation for all SAP applications, both classic SAP ABAP applications (e.g. ECC, CRM, BW) and new NetWeaver components (such as Portal, XI, and so on). In other words, the Application Server implements the Application Platform layer of the SAP NetWeaver framework.
The SAP NetWeaver Application Server has two personalities (ABAP and J2EE), which were introduced since the release 6.20 of the SAP Web Application Server (before there was only the ABAP personality). Business requirements have been increasing dramatically in the last few years, making today's development effort very time consuming. The J2EE standard was designed to address this challange, and SAP's involvement with it means that customers are not forced to maintain a 3rd-party J2EE-compatible application server anymore, effectively lowering the system landscape complexity.
With NetWeaver 2004s, the ABAP and Java personalities have been integrated to a much farther extent. SAP has introduced the Virtual Machine Container technology, enabling a Java VM to run integrated into an ABAP work process. Since the ABAP and Java VMs run in the same work process, the security and speed of the communications between the two has been significantly increased. Moreover, the VM Container architecture enables strict isolation between the active user sessions, thus a high reliability is guaranteed, which is similar to reliability provided by the standard ABAP environment.
This does not mean the J2EE engine has now become useless. In general, J2EE applications will be deployed and executed on the J2EE engine. After all it is the SAP J2EE engine that provides the J2EE specification's services. On the other hand, the execution of applications on Java VMs integrated in ABAP work processes is only intended for components developed by SAP.
Note 854170 - Activating the component "VM Container" (SMP login required)
Unbreakable Java - The Java Server that Never Goes Down
SAP VM Container: Using Process Attachable Virtual Machines to Provide Isolation and Scalability for Large Servers
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