How can I detect when an Exception's been thrown globally in Java?

Question

How can I detect when an Exception has been thrown anywhere in my application?

I'm try to auto-magically send myself an email whenever an exception is thrown anywhere in my Java Desktop Application. I figure this way I can be more proactive.

I know I could just explicitly log and notify myself whenever an exception occurs, but I'd have to do it everywhere and I might(more likely will) miss a couple.

Any suggestions?

Answer 1

You probobly don't want to mail on any exception. There are lots of code in the JDK that actaully depend on exceptions to work normally. What I presume you are more inerested in are uncaught exceptions. If you are catching the exceptions you should handle notifications there.

In a desktop app there are two places to worry about this, in the event-dispatch-thread (EDT) and outside of the EDT. Globaly you can register a class implementing java.util.Thread.UncaughtExceptionHandler and register it via java.util.Thread.setDefaultUncaughtExceptionHandler. This will get called if an exception winds down to the bottom of the stack and the thread hasn't had a handler set on the current thread instance on the thread or the ThreadGroup.

The EDT has a different hook for handling exceptions. A system property 'sun.awt.exception.handler' needs to be registerd with the Fully Qualified Class Name of a class with a zero argument constructor. This class needs an instance method handle(Throwable) that does your work. The return type doesn't matter, and since a new instance is created every time, don't count on keeping state.

So if you don't care what thread the exception occurred in a sample may look like this:

class ExceptionHandler implements Thread.UncaughtExceptionHandler {   public void uncaughtException(Thread t, Throwable e) {     handle(e);   }    public void handle(Throwable throwable) {     try {       // insert your e-mail code here     } catch (Throwable t) {       // don't let the exception get thrown out, will cause infinite looping!     }   }    public static void registerExceptionHandler() {     Thread.setDefaultUncaughtExceptionHandler(new ExceptionHandler());     System.setProperty("sun.awt.exception.handler", ExceptionHandler.class.getName());   } } 

Add this class into some random package, and then call the registerExceptionHandler method and you should be ready to go.

Answer 2

The new debugging hooks in Java 1.5 let you do this. It enables e.g. "break on any exception" in debuggers.

Here's the specific Javadoc you need.