org.springframework.util

## Class WeakReferenceMonitor

- java.lang.Object
- - org.springframework.util.WeakReferenceMonitor

-     public class WeakReferenceMonitor
      extends Object

  Track references to arbitrary objects using proxy and weak references. To monitor a handle, one should call `monitor(Object, ReleaseListener)`, with the given handle object usually being a holder that uses the target object underneath, and the release listener performing cleanup of the target object once the handle is not strongly referenced anymore.

  When a given handle becomes weakly reachable, the specified listener will be called by a background thread. This thread will only be started lazily and will be stopped once no handles are registered for monitoring anymore, to be restarted if further handles are added.

  Thanks to Tomasz Wysocki for the suggestion and the original implementation of this class!

  Since:
    1.2
  Author:
    Colin Sampaleanu, Juergen Hoeller
  See Also:
    `monitor(java.lang.Object, org.springframework.util.WeakReferenceMonitor.ReleaseListener)`

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static interface` | `WeakReferenceMonitor.ReleaseListener` Listener that is notified when the handle is being released.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `WeakReferenceMonitor()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static void` | `monitor(Object handle, WeakReferenceMonitor.ReleaseListener listener)` Start to monitor given handle object for becoming weakly reachable.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### WeakReferenceMonitor

          public WeakReferenceMonitor()

  - ### Method Detail

    - #### monitor

          public static void monitor(Object handle,
                     WeakReferenceMonitor.ReleaseListener listener)

      Start to monitor given handle object for becoming weakly reachable. When the handle isn't used anymore, the given listener will be called.
      Parameters:
        `handle` - the object that will be monitored
        `listener` - the listener that will be called upon release of the handle