Spring Tutorials

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

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

Although SOAP messages are complex, the JAX-WS API hides this complexity from the application developer. On the server side, the developer specifies the web service operations by defining methods in an interface written in the Java programming language. The developer also codes one or more classes that implement those methods. Client programs are also easy to code.

A client creates a proxy (a local object representing the service) and then simply invokes methods on the proxy. With JAX-WS, the developer does not generate or parse SOAP messages. It is the JAX-WS runtime system that converts the API calls and responses to and from SOAP messages.

The above Diagram shows Communication between a JAX-WS Web Service and a Client .The starting point for developing a JAX-WS web service is a Java class annotated with the javax.jws.WebService annotation. The @WebService annotation defines the class as a web service endpoint.

A service endpoint interface or service endpoint implementation (SEI) is a Java interface or class, respectively, that declares the methods that a client can invoke on the service. An interface is not required when building a JAX-WS endpoint. The web service implementation class implicitly defines an SEI.

You may specify an explicit interface by adding the endpointInterface element to the @WebService annotation in the implementation class. You must then provide an interface that defines the public methods made available in the endpoint implementation class. These are the basic steps for creating the web service and client:

1. Code the implementation class.
2. Compile the implementation class.
3. Use wsgen to generate the artifacts required to deploy the service.
4. Package the files into a WAR file.
5. Deploy the WAR file. The web service artifacts (which are used to communicate with clients) are generated by the Application Server during deployment.
6. Code the client class.
7. Use wsimport to generate and compile the web service artifacts needed to connect to the service.
8. Compile the client class.
9. Run the client.

JAX-WS endpoints must follow these requirements as given below:

1. The implementing class must be annotated with either the javax.jws.WebService or javax.jws.WebServiceProvider annotation.
2. The implementing class may explicitly reference an SEI through the endpointInterface element of the @WebService annotation, but is not required to do so. If no endpointInterface is specified in @WebService, an SEI is implicitly defined for the implementing class.
3. The business methods of the implementing class must be public, and must not be declared static or final.
4. Business methods that are exposed to web service clients must be annotated with javax.jws.WebMethod.
5. Business methods that are exposed to web service clients must have JAXB-compatible parameters and return types.
6. The implementing class must not be declared final and must not be abstract.
7. The implementing class must have a default public constructor.
8. The implementing class must not define the finalize method.
9. The implementing class may use the javax.annotation.PostConstruct or javax.annotation.PreDestroy annotations on its methods for life cycle event callbacks.

In this example, the implementation class, Hello, is annotated as a web service endpoint using the @WebService annotation. Hello declares a single method named sayHello, annotated with the @WebMethod annotation. @WebMethod exposes the annotated method to web service clients.

package helloservice.endpoint;
import javax.jws.WebService;
@WebService
public class Hello {
private String message = new String("Hello, ");
public void Hello() {}
@WebMethod
public String sayHello(String name) {
return message + name + ".";
}}