Capture exception in swing thread

Question

How to send exception to log4j log from java swing ?

We have much code already done and it does a lot of:

mytable.getSelectionModel().addListSelectionListener(
        new ListSelectionListener() {
            @Override
            public void valueChanged(ListSelectionEvent e) {
                ... no try catch
            }
        });

There is no try/catch. App sends npe exception to console. We need it in log4j. But don't want to change all this code (100s of line like this). What can we do?

score 8 · Accepted Answer · answered Aug 29 '11 at 14:52

8

You can set up an uncaught-exception handler that will log anything thrown by your application.

In the main method of your Swing app add these lines:

Thread.setDefaultUncaughtExceptionHandler(new LoggingExceptionHandler());
System.setProperty("sun.awt.exception.handler", LoggingExceptionHandler.class.getName());

Then implement the exception-handler like this:

package com.initech.tps;

import java.lang.Thread.UncaughtExceptionHandler;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class LoggingExceptionHandler implements UncaughtExceptionHandler
{

  private static final Logger logger = LoggerFactory.getLogger(LoggingExceptionHandler.class);

  @Override
  public void uncaughtException(Thread t, Throwable e)
  {
      logger.error("caught exception in thread: " + t.getName(), e);
  }
}

answered Aug 29 '11 at 14:52

Nathan Hughes

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sun.awt.exception.handler is to catch Exceptions when there's a modal dialog. Correct? – James P. Aug 29 '11 at 14:57
@umbr: see http://stackoverflow.com/questions/5794472/why-bother-with-setting-the-sun-awt-exception-handler-property – Nathan Hughes Aug 29 '11 at 14:57
@James: yes. but apparently with jdk7 it isn't necessary anymore – Nathan Hughes Aug 29 '11 at 14:59
JDK7 had a few bugs on it's release so chances are that JDK6 is still mainstream. – James P. Aug 29 '11 at 15:40
great answer - tx; a follow-up: we observe strange painting behaviour when this exception happens; is it because we're throwing in swing and interrupt normal paint/updates? In window that throws we begin to see buttons in weird places, scroll bars appear multiple times. If so what to do? try/catch on every swing listener? Or perhaps solition here will help resolve weird paint also? – Colin Aug 29 '11 at 17:42
@Colin: I haven't seen anything like that. Could it be you're trying to access swing components from a non-AWT thread? that's the most likely way to make a swing app do bizarre things. – Nathan Hughes Aug 29 '11 at 17:46

score 1 · Answer 2 · edited May 23 '17 at 12:34

You also can wrap the EventQueue like in this example: Catch exceptions in javax.swing application

If you want also log the exception, here I give you other option, maybe with more code, but it works properly.

import java.awt.AWTEvent;
import java.awt.EventQueue;

import javax.swing.JOptionPane;

import org.slf4j.Logger;


public class QueueEvenement extends EventQueue {
    // CONSTRUCTOR
    public QueueEvenement(Logger logger) {
        super();
        this.logger = logger;
    }


    protected void dispatchEvent(AWTEvent newEvent) {
        try {
            super.dispatchEvent(newEvent);
        } catch (Throwable t) {
            // Write log
            logger.error(String.format("Erreur inconnue (%s - %s)",
                    t.getClass().getName(), t.getLocalizedMessage()));
        }
    }
}

After you code this class, you can install the wrap with the following line:

Toolkit.getDefaultToolkit().getSystemEventQueue().push(new EventQueueProxy());

This solution have the advantage of catch only the graphic, giving you more flexibility when you have to differentite between graphic exceptions (including the event handlers) and the other possible exceptions.

Regards!

Capture exception in swing thread

2 Answers2