java.lang.management

Class MemoryNotificationInfo

Contents

  • public class MemoryNotificationInfo
extends Object
    The information about a memory notification.

    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:

    Since:
    1.5

    • Field Detail

      • MEMORY_THRESHOLD_EXCEEDED

        public static final String MEMORY_THRESHOLD_EXCEEDED
        Notification type denoting that the memory usage of a memory pool has reached or exceeded its usage threshold value. This notification is emitted by MemoryMXBean. 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. The value of this notification type is java.management.memory.threshold.exceeded.
        See Also:
        Constant Field Values

      • MEMORY_COLLECTION_THRESHOLD_EXCEEDED

        public static final String MEMORY_COLLECTION_THRESHOLD_EXCEEDED
        Notification type denoting that 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. This notification is emitted by MemoryMXBean. The value of this notification type is java.management.memory.collection.threshold.exceeded.
        See Also:
        Constant Field Values

    • Constructor Detail

      • MemoryNotificationInfo

        public MemoryNotificationInfo(String poolName,
                      MemoryUsage usage,
                      long count)
        Constructs a MemoryNotificationInfo object.
        Parameters:
        poolName - The name of the memory pool which triggers this notification.
        usage - Memory usage of the memory pool.
        count - The threshold crossing count.

    • Method Detail

      • getPoolName

        public String getPoolName()
        Returns the name of the memory pool that triggers this notification. The memory pool usage has crossed a threshold.
        Returns:
        the name of the memory pool that triggers this notification.

      • getUsage

        public MemoryUsage getUsage()
        Returns the memory usage of the memory pool when this notification was constructed.
        Returns:
        the memory usage of the memory pool when this notification was constructed.

      • getCount

        public long getCount()
        Returns 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 threshold count. For collection threshold notifications, this count will be the collection usage threshold count.
        Returns:
        the number of times that the memory usage has crossed a threshold when the notification was constructed.

Document created the 11/06/2005, last modified the 04/03/2020
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