Describe creating a Web Service using JAX-WS.

Describe creating a Web Service using JAX-WS.
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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.

You use the endpoint implementation class and the wsgen tool to generate the web service artifacts that connect a web service client to the JAX-WS runtime.

Together, the wsgen tool and the Application Server provide the Application Server's implementation of JAX-WS.

These are the basic steps for creating the web service and client:

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

Requirements of a JAX-WS Endpoint

JAX-WS endpoints must follow these requirements:

The implementing class must be annotated with either the javax.jws.WebService or javax.jws.WebServiceProvider annotation.
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.
The business methods of the implementing class must be public, and must NOT be declared static or final.
Business methods that are exposed to web service clients must be annotated with javax.jws.WebMethod.
Business methods that are exposed to web service clients must have JAXB-compatible parameters and return types.
The implementing class must NOT be declared final and must NOT be abstract.
The implementing class must have a default public constructor.
The implementing class must NOT define the finalize() method.
The implementing class may use the javax.annotation.PostConstruct or javax.annotation.PreDestroy annotations on its methods for life cycle event callbacks.
The @PostConstruct method is called by the container before the implementing class begins responding to web service clients.
The @PreDestroy method is called by the container before the endpoint is removed from operation.

Coding the Service Endpoint Implementation Class

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. sayHello returns a greeting to the client, using the name passed to sayHello to compose the greeting. The implementation class also must define a default, public, no-argument constructor.

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 + ".";
    }
}

A Simple JAX-WS Client

HelloClient is a stand-alone Java program that accesses the sayHello method of HelloService. It makes this call through a port, a local object that acts as a proxy for the remote service. The port is created at development time by the wsimport tool, which generates JAX-WS portable artifacts based on a WSDL file.

When invoking the remote methods on the port, the client performs these steps:

Uses the javax.xml.ws.WebServiceRef annotation to declare a reference to a web service. @WebServiceRef uses the wsdlLocation element to specify the URI of the deployed service's WSDL file:
```
@WebServiceRef(wsdlLocation="http://localhost:8080/helloservice/hello?wsdl")
static HelloService service;
								
```
Retrieves a proxy to the service, also known as a port, by invoking getHelloPort on the service.
```
Hello port = service.getHelloPort();
								
```
The port implements the SEI defined by the service.

Invokes the port's sayHello method, passing to the service a name.

String response = port.sayHello(name);

Here is the full source of HelloClient:

package simpleclient;

import javax.xml.ws.WebServiceRef;
import helloservice.endpoint.HelloService;
import helloservice.endpoint.Hello;

public class HelloClient {

    @WebServiceRef(wsdlLocation="http://localhost:8080/helloservice/hello?wsdl")
    static HelloService service;

    public static void main(String[] args) {
        try {
            HelloClient client = new HelloClient();
            client.doTest(args);
        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    public void doTest(String[] args) {
        try {
            System.out.println("Retrieving the port from
                     the following service: " + service);
            Hello port = service.getHelloPort();
            System.out.println("Invoking the sayHello operation
                     on the port.");

            String name;
            if (args.length > 0) {
                name = args[0];
            } else {
                name = "No Name";
            }

            String response = port.sayHello(name);
            System.out.println(response);
        } catch(Exception e) {
            e.printStackTrace();
        }
    }
}

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