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javabatch-fileloggingcmdshutdown-hook

Issue running shutdown hook in java

I am trying to get a shutdown hook to run in java. The purpose of this hook is to write into a log file that the program was terminated. The java application is compiled into a jar file and executed using a batch file, which means that the output of the application goes to a cmd.exe window. When this cmd window is closed, i want the application to log that it was closed.

The application is intended to run indefinitely and do certain tasks at a certain time. Therefore, the program is executing a series of checks within a "While true" loop. I do not understand why this hook will not log that the application is closing!

In the main method we have:

final Thread mainThread = Thread.currentThread();
Runtime.getRuntime().addShutdownHook(new Thread(new Runnable()
{
    @Override
    public void run()
    {
        try { mainThread.join(); }
        catch (InterruptedException e) { }
        mission.log("Program Closed.", true);
    }
}
));

All "mission" is, is an instance of a custom class of mine that does data logging. When you call the method "log", it has a BufferedWriter and it calls its .write(), .newLine(), and .flush() methods.

I can't seem to get the "Program Closed" line in my logfile when i kill the batch window. What am I doing wrong?

Solution

  • Forcibly killing the application, i.e. not gracefully, so the JVM doesn't know that the application is exiting, therefore the shutdown hooks are not invoked.

    Unfortunately, there is no way (in Windows, at least) to provide a mechanism that ensures that the hook is always invoked. It's just something that may be invoked, but there is no guarantee.