Java Enterprise Best Practices

Use Asynchronous Messaging Wherever Possible

Most remote method calls are synchronous: the calling thread stops and waits for a response from the server. An asynchronous method call is one in which the caller doesn’t wait for a response, or even wait to know if the call succeeded. Instead, the calling thread continues processing.

RMI doesn’t directly support asynchronous calls. Instead, you have to use a background thread to make the call. In Example 6-2, the calling thread creates a command object and drops it off in a background queue for execution. This leaves the calling thread free to immediately resume processing, instead of waiting for a response, as in the following code snippet:

BackgroundCallQueue_backgroundQueue = new BackgroundCallQueueImpl(  );
//  . . . 
_backgroundQueue.addCall(new SpecificCallToServer( . . . ));

Example 6-2 is a sample implementation of BackgroundCallQueue and BackgroundCallQueueImpl .

Example 6-2. BackgroundCallQueue.java and BackgroundCallQueueImpl.java

public interface BackgroundCallQueue { public void addCall(RemoteMethodCall callToAdd); } public class BackgroundCallQueueImpl implements BackgroundCallQueue { private LinkedList _pendingCalls; private thread _dispatchThread; public BackgroundCallQueueImpl ( ) { _stopAcceptingRequests = false; _pendingCalls = new LinkedList( ); _dispatchThread = new Thread(this, "Background Call Queue Dispatch Thread"); _dispatchThread;.start( ); } public synchronized void addCall(RemoteMethodCall callToAdd) { _pendingCalls.addCall( ...