A memory notification is emitted by MemoryMXBean when the Java virtual machine detects that the memory usage of a memory pool is exceeding a threshold value. The notification emitted will contain the memory notification information about the detected condition:

• The name of the memory pool.
• The memory usage of the memory pool when the notification was constructed.
• The number of times that the memory usage has crossed a threshold when the notification was constructed. For usage threshold notifications, this count will be the usage threshold count . For collection threshold notifications, this count will be the collection usage threshold count .

A CompositeData representing the MemoryNotificationInfo object is stored in the user data of a notification. The from method is provided to convert from a CompositeData to a MemoryNotificationInfo object. For example:

      Notification notif;

      // receive the notification emitted by MemoryMXBean and set to notif
      ...

      String notifType = notif.getType();
      if (notifType.equals(MemoryNotificationInfo.MEMORY_THRESHOLD_EXCEEDED) ||
          notifType.equals(MemoryNotificationInfo.MEMORY_COLLECTION_THRESHOLD_EXCEEDED)) {
          // retrieve the memory notification information
          CompositeData cd = (CompositeData) notif.getUserData();
          MemoryNotificationInfo info = MemoryNotificationInfo.from(cd);
          ....
      }
 

The types of notifications emitted by MemoryMXBean are:

• A usage threshold exceeded notification .
  This notification will be emitted when the memory usage of a memory pool is increased and has reached or exceeded its usage threshold value. Subsequent crossing of the usage threshold value does not cause further notification until the memory usage has returned to become less than the usage threshold value.
• A collection usage threshold exceeded notification .
  This notification will be emitted when the memory usage of a memory pool is greater than or equal to its collection usage threshold after the Java virtual machine has expended effort in recycling unused objects in that memory pool.