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Turn EJB components into Web services

Build and deploy an EJB component as a Web service with JAX-RPC

By Debu Panda, JavaWorld.com, 08/02/04

The evolution of Web-related technologies has changed the way applications in an organization communicate with customer and partner applications. Like every popular technology, Web services came like a wave and have assimilated deeply into IT organizations. Having revolutionized the IT world, Web services are here to stay. Thus, to compete in the market space, certain parts of your enterprise applications must be exposed as Web services.

The wide acceptance of Web services by companies has changed the way applications are designed, and Java developers must adapt to a service-oriented architecture. If you develop applications using J2EE, you are probably in the best position to adapt to a service-oriented architecture and expose your application as a Web service. Most J2EE application servers, such as Oracle Application Server 10g and BEA WebLogic, provide support for building and deploying Web services applications. However, J2EE 1.4 standardized building and deploying Web services applications with Java API for XML-based Remote Procedure Call (JAX-RPC).

JAX-RPC enables developers to write Web services applications by using Java classes and EJB (Enterprise JavaBeans) components. Numerous business applications have been written to EJB to encapsulate business logic in the middle tier. If you use EJB in your enterprise applications, you can easily expose them as Web services without redeveloping the business logic. This article discusses how you can build and deploy an EJB component as a Web service by using JAX-RPC and provides some guidelines for using EJB components as Web services.

What is JAX-RPC?

Before we dive into the details of developing an EJB Web service, let's quickly examine JAX-RPC. JAX-RPC, defined under Java Specification Request 101 in the Java Community Process, provides the Java API for building and accessing Web services. It can be seen as the heart and soul of building and deploying Web services with J2EE. JAX-RPC provides a simple, robust platform for building Web services applications by hiding from the application developer the complexity of mapping between XML types and Java types and the lower-level details of handling XML and SOAP (Simple Object Access Protocol) messages. It introduces a method call paradigm by providing two programming models: a server-side model, for developing Web services endpoints using Java classes or stateless EJB components, and a client-side model, for building Java clients that access Web services as local objects. JAX-RPC 1.1 mandates use of SOAP 1.1 and interoperability with other Web services built with other technologies such as Microsoft .Net. Several J2EE 1.4-compliant application servers, such as Oracle Application Server Containers for J2EE (OC4J) 10.0.3, Sun ONE (Open Network Environment) Application Server, and IBM Websphere V6, support JAX-RPC.

Developing and deploying an EJB Web service

EJB components, by design, are meant for distributed computing and are hence well suited for exposure as Web services. EJB supports declarative transactions and security, and these benefits can also be leveraged if you decide to use EJB components as Web services. J2EE 1.4 allows exposing only stateless session beans as Web services with JAX-RPC.