Swing Hacks

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Chapter 12, Miscellany

#97 Mirror an Application

HACK

second instance. As with creating single-launch applications on Windows

[Hack #84], a network socket is the best choice for a shared resource because

you need it anyway to send the events:

public void start( ) {

try {

// send events

final Socket sock = new Socket("localhost",6754);

openSender(sock);

} catch (Exception ex) {

try {

openReceiver( );

} catch (Exception ex2) {

System.out.println("exception: " + ex);

}

}

}

The start( ) method here tries to open a socket on a known port number

(6754 in this case). If the socket can be opened, then that means there is a

program on the other end waiting for a connection, in which case the code

can call

openSender( ) to start sending events. If the socket cannot be

opened, then there is no other program and this is the first running instance.

In that case, you can call

openReceiver( ) and start waiting for another pro-

gram to connect.

Send Mouse Events

To send events, you first need an output stream to send them. The java.io

package helpfully provides the ObjectOutputStream. It will take any Java

object, serialize it, and write it to the stream the class represents. Next, you

need to capture all relevant events and prepare them to go out. The AWT

Toolkit object lets you add listeners for any set of AWT events you wish.

You just need to OR together masks for the event types you want:

public void openSender(Socket sock) throws Exception {

final ObjectOutputStream out = new

ObjectOutputStream(sock.getOutputStream( ));

Toolkit.getDefaultToolkit( ).addAWTEventListener(

new AWTEventListener( ) {

public void eventDispatched(AWTEvent evt) {

try {

if(evt instanceof MouseEvent) {

MouseEvent me = (MouseEvent)evt;

out.writeObject(evt);

}

} catch (Exception ex) { }

}

},