Catching an exception when terminating a program in JAVA

Question

Is there a way to do this?

I'm coding a program that has to iterate for a very long time, and while doing so it is supposed to write to file. I want to close the stream as soon as I terminate the program manually and by doing so, avoid the risk of loosing data because of the unclosed stream. There should be a way of doing this with exception handling, but I'm not sure. Any kind of suggestion is very appreciated!

Thank you

Answer 1

in main:

try {
   startapp();
} finally {
   closeAll();
}

in closeAll() you do what you do for a safe shutdown The code in the finally block will executed even when exceptions will ocure.

Answer 2

Using exceptions to control program execution the way you are describing is poor design. It's would be much better to use a shutdown hook.

Runtime.getRuntime().addShutdownHook(new Thread() {
    @Override
    public void run() {
       // Close streams here
    }
});

This will handle most normal shutdowns just fine, though in the case of a hard halt (SIGKILL) the shutdown hooks are not guaranteed to be run. But that is no worse than if you were attempting to close the stream via a finally block.

Answer 3

I found a way! I lost so much time with this, without noticing that streams are automatically closed when the program terminates...

Data hadn't been written because I wasn't using the flush() method after the write() method, like this:

out.write(line);
out.flush();

Thank you all for your help