1 /*
   2  * Copyright (c) 2002, 2011, Oracle and/or its affiliates. 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.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * 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<String,Entry> 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     @SuppressWarnings("serial")
  65     ExpiringCache(long millisUntilExpiration) {
  66         this.millisUntilExpiration = millisUntilExpiration;
  67         map = new LinkedHashMap<>() {
  68             protected boolean removeEldestEntry(Map.Entry<String,Entry> eldest) {
  69               return size() > MAX_ENTRIES;
  70             }
  71           };
  72     }
  73 
  74     synchronized String get(String key) {
  75         if (++queryCount >= queryOverflow) {
  76             cleanup();
  77         }
  78         Entry entry = entryFor(key);
  79         if (entry != null) {
  80             return entry.val();
  81         }
  82         return null;
  83     }
  84 
  85     synchronized void put(String key, String val) {
  86         if (++queryCount >= queryOverflow) {
  87             cleanup();
  88         }
  89         Entry entry = entryFor(key);
  90         if (entry != null) {
  91             entry.setTimestamp(System.currentTimeMillis());
  92             entry.setVal(val);
  93         } else {
  94             map.put(key, new Entry(System.currentTimeMillis(), val));
  95         }
  96     }
  97 
  98     synchronized void clear() {
  99         map.clear();
 100     }
 101 
 102     private Entry entryFor(String key) {
 103         Entry entry = map.get(key);
 104         if (entry != null) {
 105             long delta = System.currentTimeMillis() - entry.timestamp();
 106             if (delta < 0 || delta >= millisUntilExpiration) {
 107                 map.remove(key);
 108                 entry = null;
 109             }
 110         }
 111         return entry;
 112     }
 113 
 114     private void cleanup() {
 115         Set<String> keySet = map.keySet();
 116         // Avoid ConcurrentModificationExceptions
 117         String[] keys = new String[keySet.size()];
 118         int i = 0;
 119         for (String key: keySet) {
 120             keys[i++] = key;
 121         }
 122         for (int j = 0; j < keys.length; j++) {
 123             entryFor(keys[j]);
 124         }
 125         queryCount = 0;
 126     }
 127 }