Client Server Architecture - Programming GPS and OpenStreetMap Applications with Java - page 157

}
...

By explicitly defining the maximum waiting time (in milliseconds), the
method call can always return within the given time window. Otherwise,
it will throw a TimeoutException . If the method does not return, or throws
a RemoteException , additional handling is necessary:

...
catch ( InterruptedException ie) { /* TODO */ }
catch ( ExecutionException ee) {
if ( ee.getCause() instanceof RemoteException )
/* TODO */

}
catch (CancellationException ce) { /* TODO */ }
catch (Exception e)
{ /* TODO: unexpected Exception ... */ }

// finally { /* TODO */ }

return null;

}

Although RemoteMethod.call can only throw RemoteException s, the excep-
tion has to be picked up via ExecutionException.getCause() , which is part
of the executor concept. If a task throws an exception, Future.get wraps
it in the ExecutionException .
In case the external client chooses to ultimately wait for a method return,
it should get the chance to cancel the task explicitly, i.e., to shut down the
application or server:

public boolean cancel( boolean mayInterruptIfRunning )
{

if ( remoteTask == null ) return false;
return remoteTask.cancel( mayInterruptIfRunning );

}

RemoteCall<V> supports waiting for client responses for a maximum time.
If there is no return (value) after the given time span, the calling (SO-)
method can implement a fall-back strategy.
Using RemoteCall.submit() , the RemoteMethod can be submitted exclu-
sively. In case the client method is void and/or the server does not bother
to wait for its return, there is no further need to use get . Nevertheless, the
result (or exception) can be retrieved at a later time via get .

Using the remote concept. After this excursion on threading concepts,
the developer needs a recipe to apply the chosen concept for his remote
method calls. In terms of program flow, the text has not reached the end
of ROServer.identify yet! The client has been mapped to the connected
Clients and is then asked to identify itself with a single line of code:

Object ID = candidate.getIdentity();