Invoking a Web Service Using Asynchronous Request-Response

The following sections describe how to invoke a Web Service using asynchronous request-response:

Overview of the Asynchronous Request-Response Feature

When you invoke a Web Service synchronously, the invoking client application waits for the response to return before it can continue with its work. In cases where the response returns immediately, this method of invoking the Web Service might be adequate. However, because request processing can be delayed, it is often useful for the client application to continue its work and handle the response later on, or in other words, use the asynchronous request-response feature of WebLogic Web Services.

You invoke a Web Service asynchronously only from a client running in a WebLogic Web Service, never from a stand alone client application. The invoked Web Service does not change in any way, thus you can invoke any deployed Web Service (both WebLogic and non-WebLogic) asynchronously as long as the application server that hosts the Web Service supports the WS-Addressing specification.

When implementing asynchronous request-response in your client, rather than invoking the operation directly, you invoke an asynchronous flavor of the same operation. (This asynchronous flavor of the operation is automatically generated by the jwsc Ant task.) For example, rather than invoking an operation called getQuote directly, you would invoke getQuoteAsync instead. The asynchronous flavor of the operation always returns void, even if the original operation returns a value. You then include methods in your client that handle the asynchronous response or failures when it returns later on. You put any business logic that processes the return value of the Web Service operation invoke or a potential failure in these methods. You use both naming conventions and JWS annotations to specify these methods to the JWS compiler. For example, if the asynchronous operation is called getQuoteAsync, then these methods might be called onGetQuoteAsyncResponse and onGetQuoteAsyncFailure.

Using Asynchronous Request-Response: Main Steps

The following procedure describes how to create a client Web Service that asynchronously invokes an operation in a different Web Service. The procedure shows how to create the JWS file that implements the client Web Service from scratch; if you want to update an existing JWS file, use this procedure as a guide.

The client Web Service is called StockQuoteClientService.
The StockQuoteClientService service is going to invoke the getQuote(String) operation of the already-deployed StockQuoteService service whose WSDL is found at the following URL:

http://localhost:7001/async/StockQuote?WSDL

It is further assumed that you have set up an Ant-based development environment and that you have a working build.xml file to which you can add targets for running the jwsc Ant task and deploying the generated service. See:

When you invoke the StockQuoteClientService Web Service, which in turn invokes the StockQuoteService Web Service, the second invoke will be asynchronous rather than synchronous.

Writing the Asynchronous JWS File

The following example shows a simple JWS file that implements a Web Service called StockQuoteClient that has a single method, asyncOperation, that in turn asynchronously invokes the getQuote method of the StockQuote service. The Java code in bold is described Coding Guidelines for Invoking a Web Service Asynchronously. See Example of a Synchronous Invoke to see how the asynchronous invoke differs from a synchronous invoke of the same operation.

Coding Guidelines for Invoking a Web Service Asynchronously

The following guidelines for invoking an operation asynchronously correspond to the Java code shown in bold in the example described in Writing the Asynchronous JWS File. These guidelines are in addition to the standard ones for creating JWS files. See Example of a Synchronous Invoke to see how the asynchronous invoke differs from a synchronous invoke of the same operation.

Import the following WebLogic-specific JWS annotations related to the asynchronous request-response feature:

import weblogic.jws.ServiceClient;
import weblogic.jws.AsyncResponse;
import weblogic.jws.AsyncFailure;

Import the JAX-RPC stub, created later by the jwsc Ant task, of the port type of the Web Service you want to invoke. The stub package is specified by the packageName attribute of the <clientgen> child element of jwsc, and the name of the stub is determined by the WSDL of the invoked Web Service.

import examples.webservices.async_req_res.StockQuotePortType;

Import the asynchronous pre- and post-call context WebLogic APIs:

import weblogic.wsee.async.AsyncCallContextFactory;
import weblogic.wsee.async.AsyncPreCallContext;
import weblogic.wsee.async.AsyncPostCallContext;

The AsyncPreCallContext and AsyncPostCallContext APIs describe asynchronous contexts that you can use for a variety of reasons in your Web Service: to set a property in the pre-context so that the method that handles the asynchronous response can distinguish between different asynchronous calls; to set and get contextual variables, such as the name of the user invoking the operation, their password, and so on; to get the name of the JAX-RPC stub that invoked a method asynchronously; and to set a time-out interval on the context.

See Javadocs for additional reference information about these APIs.

In the body of the JWS file, use the required @ServiceClient JWS annotation to specify the WSDL, name, and port of the Web Service you will be invoking asynchronously. You specify this annotation at the field-level on a variable, whose data type is the JAX-RPC port type of the Web Service you are invoking.

  @ServiceClient(
       wsdlLocation="http://localhost:7001/async/StockQuote?WSDL",
       serviceName="StockQuoteService", 
       portName="StockQuote")

  private StockQuotePortType port;

When you annotate a variable (in this case, port) with the @ServiceClient annotation, the Web Services runtime automatically initializes and instantiates the variable, preparing it so that it can be used to invoke another Web Service asynchronously.

In the method of the JWS file which is going to invoke the getQuote operation asynchronously, get a pre-call asynchronous context using the context factory:

AsyncPreCallContext apc =
    AsyncCallContextFactory.getAsyncPreCallContext();

Use the setProperty method of the pre-call context to create a property whose name and value is the same as the parameter to the getQuote method:

apc.setProperty("symbol", symbol);

Using the stub you annotated with the @ServiceClient annotation, invoke the operation (in this case, getQuote). Instead of invoking it directly, however, invoke the asynchronous flavor of the operation, which has Async added on to the end of its name. The asynchronous flavor always returns void. Pass the asynchronous context as the first parameter:

port.getQuoteAsync(apc, symbol);

For each operation you will be invoking asynchronously, create a method called onOperationnameAsyncResponse, where Operationname refers to the name of the operation, with initial letter always capitalized. The method must return void, and have two parameters: the post-call asynchronous context and the return value of the operation you are invoking. Annotate the method with the @AsyncResponse JWS annotation; use the target attribute to specify the variable whose datatype is the JAX-RPC stub and the operation attribute to specify the name of the operation you are invoking asynchronously. Inside the body of the method, put the business logic that processes the value returned by the operation.

  @AsyncResponse(target="port", operation="getQuote")
  public void onGetQuoteAsyncResponse(AsyncPostCallContext apc, 
       int quote) {
    System.out.println("-------------------");
    System.out.println("Got quote " + quote );
    System.out.println("-------------------");
  }

For each operation you will be invoking asynchronously, create a method called onOperationnameAsyncFailure, where Operationname refers to the name of the operation, with initial letter capitalized. The method must return void, and have two parameters: the post-call asynchronous context and a Throwable object, the superclass of all exceptions to handle any type of exception thrown by the invoked operation. Annotate the method with the @AsyncFailure JWS annotation; use the target attribute to specify the variable whose datatype is the JAX-RPC stub and the operation attribute to specify the name of the operation you are invoking asynchronously. Inside the method, you can determine the exact nature of the exception and write appropriate Java code.

  @AsyncFailure(target="port", operation="getQuote")
  public void onGetQuoteAsyncFailure(AsyncPostCallContext apc, 
      Throwable e) {
    System.out.println("-------------------");
    e.printStackTrace();
    System.out.println("-------------------");
  }

Example of a Synchronous Invoke

The following example shows a JWS file that invokes the getQuote operation of the StockQuote Web Service synchronously. The example is shown only so you can compare it with the corresponding asynchronous invoke shown in Writing the Asynchronous JWS File.

Updating the build.xml File When Using Asynchronous Request-Response

To update a build.xml file to generate the JWS file that invokes a Web Service operation asynchronously, add taskdefs and a build-clientService target that looks something like the following; see the description after the example for details:

Use the taskdef Ant task to define the full classname of the jwsc Ant tasks.

Update the jwsc Ant task that compiles the client Web Service to include a <clientgen> child element of the <jws> element so as to generate and compile the JAX-RPC stubs for the deployed StockQuote Web Service. The jwsc Ant task automatically packages them in the generated WAR file so that the client Web Service can immediately access the stubs. By default, the jwsc Ant task in this case generates both synchronous and asynchronous flavors of the Web Service operations in the JAX-RPC stubs. You do this because the StockQuoteClientImpl JWS file imports and uses one of the generated classes.

Disabling The Internal Asynchronous Service

By default, every WebLogic Server instance deploys an internal asynchronous Web Service that handes the asynchronous request-response feature. To specify that you do not want to deploy this internal service, start the WebLogic Server instance using the -Dweblogic.wsee.skip.async.response=true Java system property.

One reason for disabling the asynchronous service is if you use a WebLogic Server instance as a Web proxy to a WebLogic cluster. In this case, asynchronous messages will never get to the cluster, as required, because the asynchronous service on the proxy server consumes them instead. For this reason, you must disable the asynchronous service on the proxy server using the system property.

Using Asynchronous Request Response With a Proxy Server

Client applications that use the asynchronous request-response feature might not invoke the operation directly, but rather, use a proxy server. Reasons for using a proxy include the presence of a firewall or the deployment of the invoked Web Service to a cluster.

In this case, the WebLogic Server instance that hosts the invoked Web Service must be configured with the address and port of the proxy server. If your Web Service is deployed to a cluster, you must configure every server in the cluster.

WebLogic Web Services: Advanced Programming