Learn how EJB calls operate in WebSphere application Server V6.1

The order uses the EJB Enterprise javabeans™ (EJB) deployed in Ibm®websphere®application Server. Communication with these EJB components requires the use of concepts such as Internet ORB Protocol (Internet Inter-ORB PROTOCOL,IIOP) communication, JNDI lookup, and workload management. This interaction can be very complex and is usually a black box for many WebSphere users. This article provides a basic knowledge of how EJB traffic works in the context of WebSphere application Server. This article discusses communication in and out of the ORB and the definition of the basic invocation patterns and components involved in invoking the EJB components deployed in the EJB container. This article assumes that readers have a basic understanding of the j2ee™ principle and the general management knowledge of WebSphere application Server.

Introduction

For many WebSphere users, EJB communication is a black box. That is, we understand that calling method "X" returns the desired result from the EJB business logic. Under normal operating conditions, it may be sufficient to have this knowledge, since it is not usually necessary to understand the inner workings of the ORB. However, when performance issues or load-balancing problems arise, an in-depth knowledge of the ORB can greatly enhance the problem-determination process and reduce problem resolution time. As with any WebSphere component, if you understand the operating mechanism of the ORB and its associated communication protocols, you can gain further expertise in troubleshooting.

Orb

The ORB is a central part of the CORBA or common Object Request Broker Architecture (Common object ask Agent architecture), which is designed to make remote objects as usable as local objects in object-oriented distributed applications. In addition, the ORB allows these objects to communicate with each other, regardless of the specific platform, technology, and language that is used to implement those objects.

CORBA is an open, vendor-independent, distributed computing specification created by the Object Management Organization (Management GROUP,OMG), an alliance of more than 600 software vendors and other companies that promote open standard interfaces. CORBA and its Interface definition language (Interface definition Language,idl) provides a common format for representing objects that can be distributed to Java™, C, C + + Applications that are written and run on different operating systems and computers in other languages.

The ORB (object request agent) plays an integral role in the application server runtime. The ORB is implemented as part of the Java Virtual machine (Java MACHINE,JVM). IBM WebSphere Application Server includes additional code that manages the Orb instance (commonly known as an extension ORB) and also provides a plug-in framework for object services such as security. This IBM ORB implementation differs from the Sun™orb, and the code base is completely different. It is the basis on which the EJB container relies for proxy communication in order to implement the Java remote method invocation (Java sqlremote methods Invocation,rmi) interaction. RMI is a traditional way to perform remote communication in Java and communicates between Java objects using a non-standard protocol called the Java Remote Method Protocol (Java PROTOCOL,JRMP). At the most basic level, RMI is just the object-oriented version of the Java Remote Procedure call (Sqlremote Procedure call,rpc). The WebSphere application Server uses ORB to facilitate client/server RMI communication and to communicate between components.

The ORB manages inbound and outbound requests for remote Java objects, such as EJB components. The ORB provides the client with a framework to locate the EJB on the server and invoke the operations on those ejbs like a local operation. (This concept is called local-remote transparency.) The relationship between the ORB and the EJB container can be described using Figure 1.

Figure 1. ORB and EJB containers