USE HOOKS FOR CLEAN SHUTDOWNS
Part of writing a stable, robust application is ensuring that it exits 
cleanly, which may involve removing temporary files, flushing I/O 
buffers, or terminating network or database connections. The JDK 1.3 
provides a framework, called the Shutdown Hooks API, for running such 
tasks when your application exits.

A shutdown hook is a thread that is run when the JVM is in the process 
of shutting down, either as the program exits normally--typically 
through System.exit()--or as a result of a termination event, such as a 
control-C keypress in a console window.

To create a shutdown hook thread, you need to pass a Thread object to 
Runtime.addShutdownHook(). This thread object will be held until 
needed. The run() method of the Thread object should implement your 
task, and will be called as part of the shutdown process. An anonymous 
Thread class is usually sufficient, as in this sample:

Runtime.getRuntime().addShutdownHook( 
 new Thread() 
 { 
  public void run() { 
   //do shutdown work here or call external method 
  } 
 } 
);

If your application may need to remove a particular shutdown hook while 
the application is running, you'll need to create the Thread object and 
store a reference to it explicitly, which you can then pass to 
Runtime.removeShutdownHook() as needed.

Because all registered shutdown hooks are run concurrently, it's 
important that they be thread-safe. They should also terminate as 
quickly as possible as some systems will only allow applications a 
small amount of time to complete their shutdown tasks after receiving a 
termination event. For the same reason, it's usually not a good idea to 
attempt any user interaction during shutdown hook execution.

When you need to ensure that certain tasks run as part of your 
application's shutdown process, shutdown hooks are a simple solution. 
You can find more information on the Shutdown Hooks API at 
java.sun.com's Design of the Shutdown Hooks API page.
http://click.techrepublic.com/Click?q=26-KqZVIiMxfeZZsJidBHg7Z1rb89RR

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