//
// http://docs.oracle.com/javase/7/docs/jre/api/management/extension/com/sun/management/GarbageCollectionNotificationInfo.html
public class LogGC {

  public static void installGCMonitoring() {
    //get all the GarbageCollectorMXBeans - there's one for each heap generation
    //so probably two - the old generation and young generation
    List<GarbageCollectorMXBean> gcbeans = java.lang.management.ManagementFactory.getGarbageCollectorMXBeans();
    //Install a notifcation handler for each bean
    for (GarbageCollectorMXBean gcbean : gcbeans) {
      System.out.println(gcbean);
      NotificationEmitter emitter = (NotificationEmitter) gcbean;
      //use an anonymously generated listener for this example
      // - proper code should really use a named class
      NotificationListener listener = new NotificationListener() {
        //keep a count of the total time spent in GCs
        long totalGcDuration = 0;

        //implement the notifier callback handler
        @Override
        public void handleNotification(Notification notification, Object handback) {
          //we only handle GARBAGE_COLLECTION_NOTIFICATION notifications here
          if (notification.getType().equals(GarbageCollectionNotificationInfo.GARBAGE_COLLECTION_NOTIFICATION)) {
            //get the information associated with this notification
            GarbageCollectionNotificationInfo info = GarbageCollectionNotificationInfo.from((CompositeData) notification.getUserData());
            //get all the info and pretty print it
            long duration = info.getGcInfo().getDuration();
            String gctype = info.getGcAction();
            if ("end of minor GC".equals(gctype)) {
              gctype = "Young Gen GC";
            } else if ("end of major GC".equals(gctype)) {
              gctype = "Old Gen GC";
            }
            System.out.println();
            System.out.println(gctype + ": - " + info.getGcInfo().getId() + " " + info.getGcName() + " (from " + info.getGcCause() + ") " + duration + " microseconds; start-end times " + info.getGcInfo().getStartTime() + "-" + info.getGcInfo().getEndTime());
            //System.out.println("GcInfo CompositeType: " + info.getGcInfo().getCompositeType());
            //System.out.println("GcInfo MemoryUsageAfterGc: " + info.getGcInfo().getMemoryUsageAfterGc());
            //System.out.println("GcInfo MemoryUsageBeforeGc: " + info.getGcInfo().getMemoryUsageBeforeGc());

            //Get the information about each memory space, and pretty print it
            Map<String, MemoryUsage> membefore = info.getGcInfo().getMemoryUsageBeforeGc();
            Map<String, MemoryUsage> mem = info.getGcInfo().getMemoryUsageAfterGc();
            for (Entry<String, MemoryUsage> entry : mem.entrySet()) {
              String name = entry.getKey();
              MemoryUsage memdetail = entry.getValue();
              long memInit = memdetail.getInit();
              long memCommitted = memdetail.getCommitted();
              long memMax = memdetail.getMax();
              long memUsed = memdetail.getUsed();
              MemoryUsage before = membefore.get(name);
              long beforepercent = ((before.getUsed() * 1000L) / before.getCommitted());
              long percent = ((memUsed * 1000L) / before.getCommitted()); //>100% when it gets expanded

              System.out.print(name + (memCommitted == memMax ? "(fully expanded)" : "(still expandable)") + "used: " + (beforepercent / 10) + "." + (beforepercent % 10) + "%->" + (percent / 10) + "." + (percent % 10) + "%(" + ((memUsed / 1048576) + 1) + "MB) / ");
            }
            System.out.println();
            totalGcDuration += info.getGcInfo().getDuration();
            long percent = totalGcDuration * 1000L / info.getGcInfo().getEndTime();
            System.out.println("GC cumulated overhead " + (percent / 10) + "." + (percent % 10) + "%");
          }
        }
      };

      //Add the listener
      emitter.addNotificationListener(listener, null, null);
    }
  }
}