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38.6. Catching Exceptions Returned from a Remote Service
Overview
Consumers making asynchronous requests will not receive the same exceptions returned when they make synchronous requests. Any exceptions returned to the consumer asynchronously are wrapped in an
ExecutionException exception. The actual exception thrown by the service is stored in the ExecutionException exception's cause field.
Catching the exception
Exceptions generated by a remote service are thrown locally by the method that passes the response to the consumer's business logic. When the consumer makes a synchronous request, the method making the remote invocation throws the exception. When the consumer makes an asynchronous request, the
Response<T> object's get() method throws the exception. The consumer will not discover that an error was encountered in processing the request until it attempts to retrieve the response message.
Unlike the methods generated by the JAX-WS framework, the
Response<T> object's get() method throws neither user modeled exceptions nor generic JAX-WS exceptions. Instead, it throws a java.util.concurrent.ExecutionException exception.
Getting the exception details
The framework stores the exception returned from the remote service in the
ExecutionException exception's cause field. The details about the remote exception are extracted by getting the value of the cause field and examining the stored exception. The stored exception can be any user defined exception or one of the generic JAX-WS exceptions.
Example
Example 38.11, “Catching an Exception using the Polling Approach” shows an example of catching an exception using the polling approach.
Example 38.11. Catching an Exception using the Polling Approach
package demo.hw.client;
import java.io.File;
import java.util.concurrent.Future;
import javax.xml.namespace.QName;
import javax.xml.ws.Response;
import org.apache.hello_world_async_soap_http.*;
public final class Client
{
private static final QName SERVICE_NAME
= new QName("http://apache.org/hello_world_async_soap_http",
"SOAPService");
private Client() {}
public static void main(String args[]) throws Exception
{
...
// port is a previously established proxy object.
Response<GreetMeSometimeResponse> resp =
port.greetMeSometimeAsync(System.getProperty("user.name"));
while (!resp.isDone())
{
// client does some work
}
try 1
{
GreetMeSometimeResponse reply = greetMeSomeTimeResp.get();
// process the response
}
catch (ExecutionException ee) 2
{
Throwable cause = ee.getCause(); 3
System.out.println("Exception "+cause.getClass().getName()+" thrown by the remote service.");
}
}
}
The code in Example 38.11, “Catching an Exception using the Polling Approach” does the following:
If the consumer was using the callback approach the code used to catch the exception would be placed in the callback object where the service's response is extracted.
