Swing Hacks

Mirror an Application #97

Chapter 12, Miscellany

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487

HACK

them to disk, of course, but it would be even cooler to send them over the

network to another copy of the program. That way the two programs could

reuse each other’s events and become mirrors! With a global event queue

and a bit of serialization, this turns out to be quite easy.

To replicate events over the network, you need to do three things:

1. Capture all AWT events. This can be done with an

AWTEventListener.

2. Send the event objects over the network.

3. Pick the objects up on the other end of the network and repost them in

the second program.

It sounds pretty simple, but there are always a few dragons hiding in the

mist.

Set Up a Window

Every test program begins with a frame and a few components. This pro-

gram is no different, with

ApplicationMirrorTest (shown in Example 12-18)

creating a frame, button, and text field in its constructor.

Become a Server or Client

There is only one program, but it must run in two modes: one for sending

AWT events and one for receiving. If the program starts and it’s the first

instance running, then it should wait to receive events. If it’s the second

instance running, then it should send events instead. But how does the pro-

gram know if it is the first or second instance? The only real way is to look

for a shared resource. If the resource is already taken, then this must be the

Example 12-18. Simple test program for mirroring

public class ApplicationMirrorTest {

public ApplicationMirrorTest( ) {

JFrame frame = new JFrame( );

frame.getContentPane().setLayout(new FlowLayout( ));

final JButton button = new JButton("action generator");

frame.getContentPane( ).add(button);

JTextField tf = new JTextField("text field");

frame.getContentPane( ).add(tf);

frame.pack( );

frame.show( );

}