1 /*

     2  * Copyright 2002-2004 Sun Microsystems, Inc.  All Rights Reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Sun designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Sun in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    22  * CA 95054 USA or visit www.sun.com if you need additional information or

    23  * have any questions.

    24  */

    25 

    26 /*

    27  */

    28 

    29 package java.io;

    30 

    31 import java.util.Iterator;

    32 import java.util.Map;

    33 import java.util.LinkedHashMap;

    34 import java.util.Set;

    35 

    36 class ExpiringCache {

    37     private long millisUntilExpiration;

    38     private Map  map;

    39     // Clear out old entries every few queries

    40     private int queryCount;

    41     private int queryOverflow = 300;

    42     private int MAX_ENTRIES = 200;

    43 

    44     static class Entry {

    45         private long   timestamp;

    46         private String val;

    47 

    48         Entry(long timestamp, String val) {

    49             this.timestamp = timestamp;

    50             this.val = val;

    51         }

    52 

    53         long   timestamp()                  { return timestamp;           }

    54         void   setTimestamp(long timestamp) { this.timestamp = timestamp; }

    55 

    56         String val()                        { return val;                 }

    57         void   setVal(String val)           { this.val = val;             }

    58     }

    59 

    60     ExpiringCache() {

    61         this(30000);

    62     }

    63 

    64     ExpiringCache(long millisUntilExpiration) {

    65         this.millisUntilExpiration = millisUntilExpiration;

    66         map = new LinkedHashMap() {

    67             protected boolean removeEldestEntry(Map.Entry eldest) {

    68               return size() > MAX_ENTRIES;

    69             }

    70           };

    71     }

    72 

    73     synchronized String get(String key) {

    74         if (++queryCount >= queryOverflow) {

    75             cleanup();

    76         }

    77         Entry entry = entryFor(key);

    78         if (entry != null) {

    79             return entry.val();

    80         }

    81         return null;

    82     }

    83 

    84     synchronized void put(String key, String val) {

    85         if (++queryCount >= queryOverflow) {

    86             cleanup();

    87         }

    88         Entry entry = entryFor(key);

    89         if (entry != null) {

    90             entry.setTimestamp(System.currentTimeMillis());

    91             entry.setVal(val);

    92         } else {

    93             map.put(key, new Entry(System.currentTimeMillis(), val));

    94         }

    95     }

    96 

    97     synchronized void clear() {

    98         map.clear();

    99     }

   100 

   101     private Entry entryFor(String key) {

   102         Entry entry = (Entry) map.get(key);

   103         if (entry != null) {

   104             long delta = System.currentTimeMillis() - entry.timestamp();

   105             if (delta < 0 || delta >= millisUntilExpiration) {

   106                 map.remove(key);

   107                 entry = null;

   108             }

   109         }

   110         return entry;

   111     }

   112 

   113     private void cleanup() {

   114         Set keySet = map.keySet();

   115         // Avoid ConcurrentModificationExceptions

   116         String[] keys = new String[keySet.size()];

   117         int i = 0;

   118         for (Iterator iter = keySet.iterator(); iter.hasNext(); ) {

   119             String key = (String) iter.next();

   120             keys[i++] = key;

   121         }

   122         for (int j = 0; j < keys.length; j++) {

   123             entryFor(keys[j]);

   124         }

   125         queryCount = 0;

   126     }

   127 }