org.springframework.util
Class WeakReferenceMonitor

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

public class WeakReferenceMonitor
extends java.lang.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

private static class	WeakReferenceMonitor.MonitoringProcess Thread implementation that performs the actual monitoring.
static interface	WeakReferenceMonitor.ReleaseListener Listener that is notified when the handle is being released.

Field Summary

private static java.lang.ref.ReferenceQueue<java.lang.Object>	handleQueue
private static Log	logger
private static java.lang.Thread	monitoringThread
private static java.util.Map<java.lang.ref.Reference,WeakReferenceMonitor.ReleaseListener>	trackedEntries

Constructor Summary

WeakReferenceMonitor()

Method Summary

private static void	addEntry(java.lang.ref.Reference ref, WeakReferenceMonitor.ReleaseListener entry) Add entry to internal map of tracked entries.
private static boolean	keepMonitoringThreadAlive() Check whether to keep the monitoring thread alive, i.e.
static void	monitor(java.lang.Object handle, WeakReferenceMonitor.ReleaseListener listener) Start to monitor given handle object for becoming weakly reachable.
private static WeakReferenceMonitor.ReleaseListener	removeEntry(java.lang.ref.Reference reference) Remove entry from internal map of tracked entries.

Methods inherited from class java.lang.Object

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

Field Detail

logger

private static final Log logger

handleQueue

private static final java.lang.ref.ReferenceQueue<java.lang.Object> handleQueue

trackedEntries

private static final java.util.Map<java.lang.ref.Reference,WeakReferenceMonitor.ReleaseListener> trackedEntries

monitoringThread

private static java.lang.Thread monitoringThread

Constructor Detail

WeakReferenceMonitor

public WeakReferenceMonitor()

Method Detail

monitor

public static void monitor(java.lang.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

addEntry

private static void addEntry(java.lang.ref.Reference ref,
                             WeakReferenceMonitor.ReleaseListener entry)

Add entry to internal map of tracked entries. Internal monitoring thread is started if not already running.

Parameters:

ref - reference to tracked handle

entry - the associated entry

removeEntry

private static WeakReferenceMonitor.ReleaseListener removeEntry(java.lang.ref.Reference reference)

Remove entry from internal map of tracked entries.

Parameters:

reference - the reference that should be removed

Returns:

entry object associated with given reference

keepMonitoringThreadAlive

private static boolean keepMonitoringThreadAlive()

Check whether to keep the monitoring thread alive, i.e. whether there are still entries being tracked.