16.  Building Web Services with JAX-WS

Chapter 16

Building Web Services with JAX-WS

JAX-WS stands for Java API for XML Web Services. JAX-WS is a technologyfor building web services and clients that communicate using XML. JAX-WS allows developersto write message-oriented as well as RPC-oriented web services.

In JAX-WS, a web service operation invocation is represented by an XML-based protocolsuch as SOAP. The SOAP specification defines the envelope structure, encoding rules, andconventions for representing web service invocations and responses. These calls and responses aretransmitted as SOAP messages (XML files) over HTTP.

Although SOAP messages are complex, the JAX-WS API hides this complexity from theapplication developer. On the server side, the developer specifies the web service operationsby defining methods in an interface written in the Java programming language. The developeralso codes one or more classes that implement those methods. Client programs arealso easy to code. A client creates a proxy (a local object representingthe service) and then simply invokes methods on the proxy. With JAX-WS, thedeveloper does not generate or parse SOAP messages. It is the JAX-WS runtimesystem that converts the API calls and responses to and from SOAP messages.

With JAX-WS, clients and web services have a big advantage: the platform independenceof the Java programming language. In addition, JAX-WS is not restrictive: a JAX-WSclient can access a web service that is not running on the Javaplatform, and vice versa. This flexibility is possible because JAX-WS uses technologies definedby the World Wide Web Consortium (W3C): HTTP, SOAP, and the Web ServiceDescription Language (WSDL). WSDL specifies an XML format for describing a service asa set of endpoints operating on messages.

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