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Java > Open Source Codes > net > mlw > vlh > adapter > ValueListAdapterCacheDecorator


1 /**
2  * Copyright (c) 2003 held jointly by the individual authors.
3  *
4  * This library is free software; you can redistribute it and/or modify it
5  * under the terms of the GNU Lesser General Public License as published
6  * by the Free Software Foundation; either version 2.1 of the License, or
7  * (at your option) any later version.
8  *
9  * This library is distributed in the hope that it will be useful, but
10  * WITHOUT ANY WARRANTY; with out even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12  * GNU Lesser General Public License for more details.
13  *
14  * You should have received a copy of the GNU Lesser General Public License
15  * along with this library; if not, write to the Free Software Foundation,
16  * Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
17  *
18  * > http://www.gnu.org/copyleft/lesser.html
19  * > http://www.opensource.org/licenses/lgpl-license.php
20  */
21 package net.mlw.vlh.adapter;
22
23 import net.mlw.vlh.DefaultListBackedValueList;
24 import net.mlw.vlh.ValueList;
25 import net.mlw.vlh.ValueListAdapter;
26 import net.mlw.vlh.ValueListInfo;
27
28 /** This decorator is a lazy way to implement caching. This is ideal for
29  * select boxes and the like.
30  *
31  * <p>
32  * Note that to make this thread safe sorting and paging must
33  * be defined in the parent ValueListAdapter
34  * </p>
35  *
36  * @author mwilson
37  */
38 public class ValueListAdapterCacheDecorator implements ValueListAdapter
39 {
40     /** The duration in milliseconds to allow cached data to stick around. **/
41     private long cacheTimeout = Long.MAX_VALUE;
42     /** The time in milliseconds the cache was created. **/
43     private long cacheCreateTime = -1;
44     /** The time in milliseconds the cache should be refreshed. **/
45     private long nextRefresh = System.currentTimeMillis();
46     /** The source for the data. **/
47     private ValueListAdapter decoratedValueListAdapter;
48     /** The cached valuelist. **/
49     private ValueList valueList;
50
51     /**
52      * @see net.mlw.vlh.ValueListAdapter#getAdapterType()
53      */
54     public int getAdapterType()
55     {
56         return decoratedValueListAdapter.getAdapterType();
57     }
58
59     /**
60      * @see net.mlw.vlh.ValueListAdapter#getValueList(java.lang.String, net.mlw.vlh.ValueListInfo)
61      */
62     public ValueList getValueList(String JavaDoc name, ValueListInfo info)
63     {
64         //Check to see if we ever invalidate the cache.
65 if (valueList == null || cacheTimeout != Long.MAX_VALUE)
66         {
67             if (nextRefresh < System.currentTimeMillis())
68             {
69                 cacheCreateTime = System.currentTimeMillis();
70                 nextRefresh = cacheCreateTime + cacheTimeout;
71                 valueList = decoratedValueListAdapter.getValueList(name, info);
72             }
73         }
74
75         return new DefaultListBackedValueList(valueList.getList(), valueList.getValueListInfo());
76     }
77
78     /** Sets the duration in milliseconds to allow
79      * cached data to stick around.
80      *
81      * @param cachTimeout Duration in milliseconds.
82      */
83     public void setCacheTimeout(long cacheTimeout)
84     {
85         this.cacheTimeout = cacheTimeout;
86     }
87
88     /** The underling ValueListAdapter that retrieves the ValueList
89      * to be cached.
90      *
91      * @param decoratedValueListAdapter The parent ValueListAdapter.
92      */
93     public void setParent(ValueListAdapter decoratedValueListAdapter)
94     {
95         this.decoratedValueListAdapter = decoratedValueListAdapter;
96     }
97 }
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