Logging runtime exceptions

[Rob Marshall]

Hi,

I apologize if this has already been asked, but I wasn't sure what to search for...

I'm writing an application (my first one in Java, yeah! ) that uses dozens of classes spread over several files, etc. Normally the application will be run from a menu with no one sitting at the console watching it, so I need to be able to have all exception stack traces for any runtime exceptions, anything not already accounted for by a "catch", sent to a log file. Is there an easy way to make sure that any uncaught runtime exceptions will be "magically" caught and sent to the logs?

It's OK if the program exits, but I don't want to be stuck in a situation where the program dies without leaving some clues as to what happened.

I assume that I could just put a catch block like the following in every class:

try {
whatever...hits runtime exception, out of memory, segmentation fault, who knows...
} catch (Exception e) {
log.error(e.printStackTrace());
}

but since I don't know when/where it will happen, I'd prefer to be able to set this up in one place and have it work for all the classes/files. Is that possible?

Thanks,

Rob

[Rob Marshall]

I just found: Thread.setUncaughtExceptionHandler(), but that's as of 1.5. My code will be running on 1.4.2...

How was this done prior to 1.5?

Thanks,

Rob

[Rob Marshall]

OK, it looks like the answer is to use ThreadGroup and uncaughtException, here's a simple example of something I found and modified slightly:

import java.io.*;
import org.apache.log4j.*;

public class UncaughtExceptionExample {
	static Logger log = Logger.getLogger("UncaughtExceptionExample");

	public static class UncaughtThreadGroup extends ThreadGroup {

		public UncaughtThreadGroup(String s) {
			super(s);
		}

		public void uncaughtException(Thread thread, Throwable throwable) {
			final Writer trace = new StringWriter();
			final PrintWriter pw = new PrintWriter(trace);
			throwable.printStackTrace(pw);
			log.error("Thread " + thread.getName() + " died, exception was: ");
			log.error(trace.toString());
		}
	}

	public static ThreadGroup uncaughtThreads = new UncaughtThreadGroup("Catch Threads");

	public static class UncaughtThread extends Thread {
		public UncaughtThread(String s) {
			super(uncaughtThreads, s);
		}

		public void run() {
			callFirst();
		}

	}

	private static void callFirst() {
		callSecond();
	}

	private static void callSecond() {
		String s = null;
		System.out.println("hi: " + s.getBytes());
	}

	public static void main(String[] args) {
		Thread t = new UncaughtThread("Catch Thread");
		t.start();
	}
}

Rob