Google App Engine - Configure default logger to send email

Question

In my GAE/J application, how would I configure the default logger to report errors via email?

Answer 1

The MailHandler included with JavaMail 1.5.3 and later have built in support for Google App Engine. Make sure you are using the most current version of JavaMail.

For GAE/J you can download the logging-mailhandler.jar and include it in your project.

    com.sun.mail  
    logging-mailhandler  
    1.5.3 
    system
    FILE_PATH_TO/logging-mailhandler.jar

Otherwise, can use the java.net Maven repository or Maven Central and pull the dependency by groupid=com.sun.mail and artifactId=logging-mailhandler.

    com.sun.mail  
    logging-mailhandler  
    1.5.3 

After the dependency is setup, then configure your logging.properties to contain the correct log settings and email envlope. Here is a sample logging.properties file:

    # A default java.util.logging configuration.
    # (All App Engine logging is through java.util.logging by default).
    #
    # To use this configuration, copy it into your application's WEB-INF
    # folder and add the following to your appengine-web.xml:
    # 
    # 
    #   
    # 
    #

    # Set the default logging level for all loggers to INFO
    .level = INFO
    java.util.logging.MemoryHandler.level=ALL
    java.util.logging.MemoryHandler.push=WARNING
    #com.sun.mail.util.logging.CompactFormatter.format=%1$tc %2$s%n%4$s: %5$s%6$s%n
    #com.sun.mail.util.logging.MailHandler.formatter=com.sun.mail.util.logging.CompactFormatter
    com.sun.mail.util.logging.MailHandler.level=WARNING
    com.sun.mail.util.logging.MailHandler.mail.from=me@example.com
    com.sun.mail.util.logging.MailHandler.mail.to=me@example.com
    #com.sun.mail.util.logging.MailHandler.pushLevel=OFF
    #com.sun.mail.util.logging.MailHandler.subject=com.sun.mail.util.logging.CollectorFormatter
    com.sun.mail.util.logging.MailHandler.verify=limited

Next create code to install the MailHandler because the LogManager won't be able to see the logging-mailhandler.jar.

Here is an example of a ServletContextListener that will install the MailHandler on the root logger.

/**
 * Modify web.xml to include
 *  
 *       Install MailHandler on root logger.
 *       PACKAGE_NAME_FOR.MailHandlerConfig
 *  
 */
    import com.sun.mail.util.logging.*;
    import static com.google.appengine.api.ThreadManager.backgroundThreadFactory;
    import java.util.Arrays;
    import static java.util.concurrent.Executors.newScheduledThreadPool;
    import java.util.concurrent.Future;
    import java.util.concurrent.ScheduledExecutorService;
    import java.util.concurrent.TimeUnit;
    import java.util.logging.Formatter;
    import java.util.logging.Handler;
    import java.util.logging.Level;
    import java.util.logging.Logger;
    import java.util.logging.MemoryHandler;
    import javax.servlet.ServletContextEvent;
    import javax.servlet.ServletContextListener;

    public class MailHandlerConfig implements ServletContextListener, Runnable {

        private static final String LOGGER_NAME = "";
        private static final Logger logger = Logger.getLogger(LOGGER_NAME);
        private volatile ScheduledExecutorService ses;
        private volatile Future task;
        private volatile Handler handler;

        @Override
        public void contextInitialized(ServletContextEvent sce) {
            MailHandler mh = new MailHandler();
            mh.setSubject(defaultSubject());
            handler = mh;
            try {
                handler = new MemoryHandler(mh, mh.getCapacity(), mh.getPushLevel());
                ses = newScheduledThreadPool(1, backgroundThreadFactory());
                task = ses.scheduleAtFixedRate(this, 30L, 30L, TimeUnit.MINUTES);
            } catch (RuntimeException | LinkageError re) {
                logger.log(Level.WARNING, "Unable to create push thread.", re);
                Level lvl = mh.getLevel();
                if (lvl.intValue() < mh.getPushLevel().intValue()) {
                    mh.setPushLevel(lvl);
                    handler = mh;
                    logger.log(Level.WARNING, "Forcing push level to {0}.", lvl);
                }
            }
            logger.addHandler(handler);
            logger.log(Level.INFO, "Application initialized. {0}",
                    Arrays.toString(logger.getHandlers()));
        }

        @Override
        public void contextDestroyed(ServletContextEvent sce) {
            //Never called under GAE.
            try {
                Future f = task;
                if (f != null) {
                    f.cancel(false);
                }
            } catch (RuntimeException ignore) {
            }

            try {
                ScheduledExecutorService e = this.ses;
                if (e != null) {
                    e.shutdown();
                }
            } catch (RuntimeException ignore) {
            }

            try {
                Handler h = handler;
                if (h != null) {
                    h.close();
                    logger.removeHandler(h);
                }
            } catch (RuntimeException ignore) {
            }
            run();
        }

        @Override
        public void run() {
            for (Handler h : logger.getHandlers()) {
                try {
                    if (h instanceof MemoryHandler) {
                        ((MemoryHandler) h).push();
                    }
                    h.flush();
                } catch (RuntimeException ignore) {
                }
            }
        }

        private static Formatter defaultSubject() {
            return new CollectorFormatter(
                    "{0}{1}{2}{4,choice,-1#|0#|0<... {4,number,integer} more}",
                    new CompactFormatter("%7$#.160s"),
                    new SeverityComparator());
        }
    }