com.samskivert.util.ExpiringReference Maven / Gradle / Ivy
//
// samskivert library - useful routines for java programs
// Copyright (C) 2001-2011 Michael Bayne, et al.
// http://github.com/samskivert/samskivert/blob/master/COPYING
package com.samskivert.util;
/**
* Provides a simple way of tracking a resource that should become stale after
* a certain time period. This is useful for caching data that was expensive to
* compute and should be cached for some time before being recreated.
*
* Note: the data will not be unreferenced and thus garbage
* collectable until it has been requested at least once after it has expired.
* Thus expiring references must be combined with an {@link LRUHashMap} if
* memory conservation is also desired.
*/
public class ExpiringReference
{
/**
* Creates an expiring reference with the supplied value and expiration time.
*/
public static ExpiringReference create (T value, long expireMillis)
{
return new ExpiringReference(value, expireMillis);
}
/**
* Gets the value from an expiring reference but returns null if the supplied reference
* reference is null.
*/
public static T get (ExpiringReference value)
{
return (value == null) ? null : value.getValue();
}
/**
* Creates an reference to the specified value that will expire in the
* specified number of milliseconds.
*/
public ExpiringReference (T value, long expireMillis)
{
_value = value;
_expires = System.currentTimeMillis() + expireMillis;
}
/**
* Returns the value with which we were created or null if the value has
* expired.
*/
public T getValue ()
{
// if the value is still around and it's expired, clear it
if (_value != null && System.currentTimeMillis() >= _expires) {
_value = null;
}
// then return the value (which may be cleared to null by now)
return _value;
}
protected T _value;
protected long _expires;
}