JAX-WS Web服务，如何工作

Question

I'm read official oracle tutorial, but dont understand this full. I'm glad if we answer my questions.

Question 1. What's conceptual difference between JAX-WS Web Service and RMI? Both RMI and JAX-WS can invoke remote method.

Question 2. Why we cant use servlets only for the features, that can be implemented by JAX-WS? Just declare init servlet's methods.

Question 3. As i understand, web service JAX-WS can't get http response and http request whithout servlets, for example. It's just set of endpoints classes, whose contains WebMethods with their implementation. Ie if we want to communicated with service through web-client we must declare appropriate servlet for this needs. This servlet will parse http request, invoke appropriate @WebMethod generate and sent http response. Is it correct?

Question 4. Is WSDL document just xml -file whose contain description availabl @WebMethod by this WEbService and all?

Question 5. From the official tutorial:

A client creates a proxy (a local object representing the service) and then simply invokes methods on the proxy.

Does client create a proxy based on service's WSDL -document?

Answer 1

My take on the answers in order:

• RMI invokes methods of remote Java objects directly from objects in other Java virtual machines and uses object serialization to marshal and unmarshal parameters. Notice how all of this is Java-specific. JAX-WS is about a Java API for leveraging standards (SOAP, WSDL, etc) to facilitate broader interoperability instead. As a result, applications of all kinds can talk to each other--not just Java to Java.

• With JAX-WS, you are using servlets. It's just that the specification provides an abstraction on top of the Servlet API. It is always better to work with abstractions than with low-level implementation details. This frees you up to work on the interesting stuff and helps you avoid mistakes.

• I don't quite follow this question, but HttpServlet is the Java EE abstraction for all HTTP communication. So JAX-WS, JAX-RS, and other specifications rely on HttpServlet. You don't have to specify the servlets or anything. That's one of the many low-level details the abstractions free you from.

• WSDL is a standard that transcends platform or implementation. In other words, it has no idea about @WebMethod or any other implementation-specific details. It just defines the interface for interacting with the service.

• Yes. WSDL's aren't meant to be consumed by humans. They define the interface for interacting with the service, and clients (Java, .NET, whatever) use these to auto-generate stubs for you to use to call the services defined in the WSDL. The client generates the SOAP request for you and processes the SOAP response for you.