Get notification on a Java process termination

Question

There is a console Java application which is supposed to run untill it is stopped by Ctrl+C or closing the console window. How that application can be programmed to execute a clean up code before exit?

Answer 1

You could use a Shutdown Hook.

Basically you need to create a Thread which will perform your shutdown actions, and then add it as a shutdown hook. For example:

class ShutdownHook extends Thread
{
    public void run()
    {
        // perform shutdown actions
    }
}

// Then, somewhere in your code

Runtime.getRuntime().addShutdownHook(new ShutdownHook())

Answer 2

A Shutdown hook is the way to go, but be aware that there is no guarantee that the code is actually executed. JVM crashes, power failures, or a simple "kill -9" on your JVM can prevent the code from cleaning up. Therefore you must ensure that your program stays in a consistent state even if it has been aborted abruptly.

Personally, I simply use a database for all state-storage. Its transactions model makes sure that the persistent storage is in a sane state no matter what happens. They spend years making that code fool-proof, so why should I waste my time on problems already solved.