Monday May 11, 2009

Asynchronous Webservice

Asynchronous Webservice Client: Client side asynchrony can be achieved using the following,



  1. Async Polling

  2. Async Callback-handler


1. Create a Calculator Application using the examples which comes with glassfishesb/netbeans


 calculator app


2.  Observe the webservice client for the above, note the webservice interface has a single operation which is by default a synchronous call, we will see how to generate the interface which makes the same call in an asynchronous way



3. Enable Asynchronous Client : note the interface now has two more operations


enable asyn client


4. How to invoke using the above generated service endpoint interface ,


Async Polling


The client application will invoke the async polling operation on the stub and check for a response on the Response object. The response is available when Response.isDone returns true.



javax.xml.ws.Response<com.sun.CalculateResponse> resp = port.calculateAsync(x, y);
 while(!resp.isDone()) {
  // do something


}
System.out.println("Result = "+resp.get().getReturn());
 



Async CallbackHandler


In this case the  client application has to provide an AsyncHandler by implementing the javax.xml.ws.AsyncHandler<T> interface.



// Async callback handler


class CalculatorWSCallbackHandler implements javax.xml.ws.AsyncHandler<com.sun.CalculateResponse> {
    private com.sun.CalculateResponse output;


    public void handleResponse(javax.xml.ws.Response<com.sun.CalculateResponse> response) {
        try {
            output = response.get();
        } catch(Exception ex) {
            // handle exception
        }
    }


    com.sun.CalculateResponse getResponse() {
         return output;
    }
}


// The async handler is then passed as a parameter of the async callback method:


CalculatorWSCallbackHandler asyncHandler = new CalculatorWSCallbackHandler();
 // process asynchronous response here
 java.util.concurrent.Future<? extends java.lang.Object> result = port.calculateAsync(x, y, asyncHandler);
 while(!result.isDone()) {
  // do something
 }
 out.println("Result = "+asyncHandler.getResponse().getReturn());
  



5. Using the Dispatch Api


Four types of MEP are supported using the dispatch API



  • Object response = dispatch.invoke(T);

  • dispatch.invokeOneway(T);

  • Response<T> response = dispatch.invokeAsync(T);

  • Future<?> response = dispatch.invokeAsync(T, AsyncHandler);



The example shows how the asynchronous invocation can be made while using the SOAPMessage

Aysnc Polling



Response<SOAPMessage> res = dispatch.invokeAsync(soapMessage);
 while (!res.isDone()) {
     //do some work
 }
 SOAPMessage soapM = res.get();



Async CallbackHandler



class ResponseHandler implements javax.xml.ws.AsyncHandler<SOAPMessage> {



 SOAPMessage output = null;


 public void handleResponse(Response<SOAPMessage> arg0) {
     try {
  output = arg0.get();
     } catch (Exception e) {
  // handle exception
     }
 }
 SOAPMessage getResponse() {
     return output;
 }
      }
 



 ResponseHandler rhandler = new ResponseHandler();
 Future<? extends java.lang.Object> f = dispatch.invokeAsync(message, rhandler);
 while(!f.isDone()){
     //do some work
 }
 
 SOAPMessage m = rhandler.getResponse();



Using WS-Addressing


WS-addressing supports asynchronous MEP , here is one example taken from the specification, Note the replyTo part of the Request message, Any service implementing ws-addressing specification will send the response message based on the replyTo Message addresing property



Request 



<S:Envelope
  <wsa:MessageID>abc</wsa:MessageID>
    <wsa:ReplyTo>
    <wsa:Address>http://abc.com/client1</wsa:Address>
    </wsa:ReplyTo>
    <wsa:To S:mustUnderstand="1">http://fabrikam123.example</wsa:To>
    <wsa:Action>http://fabrikam123.example/mail/Delete</wsa:Action>
  </S:Header>
  <S:Body>
    <f123:Delete>    
       <maxCount>42</maxCount>
    </f123:Delete>
  </S:Body>
</S:Envelope>



Response



<S:Envelope
    <wsa:MessageID>xyz</wsa:MessageID>
    <wsa:RelatesTo>abc</wsa:RelatesTo>
    <wsa:To S:mustUnderstand="1">
     
http://abc.com/client1
    </wsa:To>
    <wsa:Action>http://fabrikam123.example/mail/DeleteAck</wsa:Action>
  </S:Header>
  <S:Body>
    <f123:DeleteAck/>
  </S:Body>
</S:Envelope>




 


The diagram below shows the flow  of messages


ws-addressing


Note: if replyTo contains an anonymous URI


http://schemas.xmlsoap.org/ws/2003/03/addressing/role/anonymous



When an application/client uses anonymous URI, it says that there is no real endpoint available for this address. Using the anonymous URI is equivalent to not using the ReplyTo header, the response must flow back in the HTTP response message. The web-service must be able to dynamically switch between synchronous and asynchronous modes on the basis of replyTo or faultTo headers.


 


More info



  1. Async Client

  2. WS-Addressing

Tuesday Mar 03, 2009

WS-Addressing and stateful webservice

 


WS-addressing and its use



  • Provides transport-neutral mechanisms to address Web services and messages.

  • Stateful webservice, Web services are usually stateless, , however it is possible to enable webservice to be stateful i.e. to share multiple instances of service endpoints between subsequent invocation.

  • Simple and complex Message Exchange Patterns

  • Used for other WS-\* specification like reliable Messaging, WS-MetadataExchange, WS-Security


WS-Addressing and stateful webservice


We will dive in details how stateful sebservice is created? how a client can access the same? and how metro/jax-ws maintain the state in between subsequent invocation?, We will make use of the examples which comes with metro/jax-ws RI


Examples 



Server (Book.java and BookStore.java)



@Stateful @WebService @Addressing
public class Book {
    private final String id;
    private volatile List<String> reviews = new ArrayList<String>();
    public Book(String id) {
        this.id = id;
    }
    public String getId() {
        return id;
    }
    public synchronized void postReview(String review) {
        List<String> l = new ArrayList<String>(reviews);
        l.add(review);
        reviews = l;
    }
    public List<String> getReviews() {
        return reviews;
    }
    public boolean equals(Object that) {
        if (that == null || this.getClass() != that.getClass()) return false;
        return this.id.equals(((Book)that).id);
    }
    public int hashCode() {
        return id.hashCode();
    }


    public static StatefulWebServiceManager<Book> manager;
}



@WebService
public class BookStore {
    public W3CEndpointReference getProduct(String id) {
        return Book.manager.export(new Book(id));
    }
}
 




See the Book.java which is stateful webservice, this is done by declaring Stateful annotation on a Book.java class. Note the class also have a public static method/field that takes StatefulWebServiceManager. Once the service is deployed the jax-ws does the resource injection on the field or the method. A stateful web service (Book.java) does not need to have a default constructor. Most of the time user would to define a constructor that takes some arguments, so that each instance carries certain state. Each instance of a stateful web service( Book.java) is identified by an unique EndpointReference. BookStore.java creates an instance of a class, JAX-WS RI assign a unique EPR for the instance as follows   Book.manager.export(new Book(id))



Client
        BookStore bookstore = new BookStoreService().getBookStorePort();
        BookService service = new BookService();


        1. Book book1 = service.getPort(bookstore.getProduct("abc001"), Book.class);
        2.  book1.getId();
        3. book1.postReview("This book is great!");
        4. book1.getReviews();


        similar code for book2....




Once the client runtime receives the EPR info , it uses the EPR info in the subsequent call, i.e When client send messages to this EPR, the JAX-WS RI makes sure that the particular exported instance associated with that EPR will receive a service invocation. We will see shortly how this is achieved


 


Digging Deeper 


We will trace the soap request response for the client code (line 1, 2, and 3). This will give an clear idea how an Endpoint can associate the request with an exported instance of an EPR, and how the exported instance is  identified using an unique Identifier. 


1. Invoke BookStore service( bookstore.getProduct("abc001")) , Note the soap request-response, The response contain the EPR details which contains the address and the unique <jaxws:objectid>, note this objectid is used in subsequent call to the BookService, and this how the jaxws RI find out which instance of the EPR will get the invocation




get endpoint reference 



2. book1.getId(); note the soap request, here the jax-ws inserts the required addressing headers and the <jaxws:objectid>,  





get id of the book 






3.  book1.postReview("This book is great!"); note the soap request, here also the jax-ws inserts the required addressing headers and the <jaxws:objectid>,  





post review of the book



 





 More Info



 


 

Thursday Feb 12, 2009

Mtom, Soap with Attachment in Composite Applications

Mtom is used to optimize the transmission of soap message over the wire. MTOM uses a  wire format of a SOAP message by selectively encoding portions of the message, whilst still presenting an XML Infoset to the SOAP application. Optimization is available only for element content that is in a canonical lexical representation of the xs:base64Binary data type  


This article talks how to use mtom in glassfish esb, what are the limitation current implementation has , how to overcome the same

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