Asynchronous JAX-RS - RESTful Java with JAX-RS 2.0 - page 203

Callbacks

The AsyncResponse interface also allows you to register callback objects for other types of
events:

package package javax . ws . rs . container ;

public public interface interface CompletionCallback CompletionCallback {

public public void void onComplete ( Throwable throwable );

}

CompletionCallback.onComplete() is called after the response has been sent to the client.
The Throwable is set to any unmapped exception thrown internally when processing a re-
sume() . Otherwise, it is null .

package package javax . ws . rs . container ;

public public interface interface ConnectionCallback ConnectionCallback {

public public void void onDisconnect ( AsyncResponse response );

}

The JAX-RS container does not require implementation of the ConnectionCallback . It al-
lows you to be notified if the socket connection is disconnected while processing the re-
sponse.

You enable callbacks by invoking the AsyncResponse.register() methods. You can pass
one or more classes that will be instantiated by the JAX-RS container, and you can pass one
or more instances:

response . register ( MyCompletionCallback . class );
response . register ( new new MyConnectionCallback ());

Callbacks are generally used to receive notification of error conditions caused after invoking
resume() . You may have resources to clean up or even transactions to roll back or undo as a
result of an asynchronous failure.

Use Cases for AsyncResponse

The examples used in the previous section were really contrived to make it simple to explain
the behavior of the asynchronous APIs. As I mentioned before, there is a specific set of use
cases for async response processing. Let's go over it.