KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > org > apache > turbine > services > cache > RefreshableCachedObject


1 package org.apache.turbine.services.cache;
2
3 /*
4  * Copyright 2001-2004 The Apache Software Foundation.
5  *
6  * Licensed under the Apache License, Version 2.0 (the "License")
7  * you may not use this file except in compliance with the License.
8  * You may obtain a copy of the License at
9  *
10  * http://www.apache.org/licenses/LICENSE-2.0
11  *
12  * Unless required by applicable law or agreed to in writing, software
13  * distributed under the License is distributed on an "AS IS" BASIS,
14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  * See the License for the specific language governing permissions and
16  * limitations under the License.
17  */
18
19 /**
20  * The idea of the RefreshableCachedObject is that, rather than
21  * removing items from the cache when they become stale, we'll tell them to
22  * refresh themselves instead. That way they'll always be in the
23  * cache, and the code to refresh them will be run by the background
24  * thread rather than by a user request thread. You can also set a TTL (Time
25  * To Live) for the object. This way, if the object hasn't been touched
26  * for the TTL period, then it will be removed from the cache.
27  *
28  * This extends CachedObject and provides a method for refreshing the
29  * cached object, and resetting its expire time.
30  *
31  * @author <a HREF="mailto:nissim@nksystems.com">Nissim Karpenstein</a>
32  * @author <a HREF="mailto:hps@intermeta.de">Henning P. Schmiedehausen</a>
33  * @version $Id: RefreshableCachedObject.java,v 1.5.2.2 2004/05/20 03:05:19 seade Exp $
34  */
35 public class RefreshableCachedObject
36         extends CachedObject
37 {
38
39     /**
40      * How long to wait before removing an untouched object from the cache.
41      * Negative numbers mean never remove (the default).
42      */
43     private long timeToLive = -1;
44
45     /**
46      * The last time the Object was accessed from the cache.
47      */
48     private long lastAccess;
49
50     /**
51      * Constructor; sets the object to expire in the default time (30
52      * minutes).
53      *
54      * @param o The object you want to cache.
55      */
56     public RefreshableCachedObject(Refreshable o)
57     {
58         super(o);
59         lastAccess = System.currentTimeMillis();
60     }
61
62     /**
63      * Constructor.
64      *
65      * @param o The object to cache.
66      * @param expires How long before the object expires, in ms,
67      * e.g. 1000 = 1 second.
68      */
69     public RefreshableCachedObject(Refreshable o,
70                                    long expires)
71     {
72         super(o, expires);
73         lastAccess = System.currentTimeMillis();
74     }
75
76     /**
77      * Sets the timeToLive value
78      *
79      * @param timeToLive the new Value in milliseconds
80      */
81     public synchronized void setTTL(long timeToLive)
82     {
83         this.timeToLive = timeToLive;
84     }
85
86     /**
87      * Gets the timeToLive value.
88      *
89      * @return The current timeToLive value (in milliseconds)
90      */
91     public synchronized long getTTL()
92     {
93         return timeToLive;
94     }
95
96     /**
97      * Sets the last acccess time to the current time.
98      */
99     public synchronized void touch()
100     {
101         lastAccess = System.currentTimeMillis();
102     }
103
104     /**
105      * Returns true if the object hasn't been touched
106      * in the previous TTL period.
107      */
108     public synchronized boolean isUntouched()
109     {
110         if (timeToLive < 0)
111             return false;
112
113         if (lastAccess + timeToLive < System.currentTimeMillis())
114             return true;
115         else
116             return false;
117     }
118
119     /**
120      * Refresh the object and the created time.
121      */
122     public void refresh()
123     {
124         Refreshable r = (Refreshable) getContents();
125         synchronized (this)
126         {
127             created = System.currentTimeMillis();
128             r.refresh();
129         }
130     }
131 }
132
Popular Tags