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
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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  *
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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 
Entry(long timestamp, String val)48         Entry(long timestamp, String val) {
49             this.timestamp = timestamp;
50             this.val = val;
51         }
52 
timestamp()53         long   timestamp()                  { return timestamp;           }
setTimestamp(long timestamp)54         void   setTimestamp(long timestamp) { this.timestamp = timestamp; }
55 
val()56         String val()                        { return val;                 }
setVal(String val)57         void   setVal(String val)           { this.val = val;             }
58     }
59 
ExpiringCache()60     ExpiringCache() {
61         this(30000);
62     }
63 
64     @SuppressWarnings("serial")
ExpiringCache(long millisUntilExpiration)65     ExpiringCache(long millisUntilExpiration) {
66         this.millisUntilExpiration = millisUntilExpiration;
67         map = new LinkedHashMap<String,Entry>() {
68             @Override
69             protected boolean removeEldestEntry(Map.Entry eldest) {
70               return size() > MAX_ENTRIES;
71             }
72           };
73     }
74 
get(String key)75     synchronized String get(String key) {
76         if (++queryCount >= queryOverflow) {
77             cleanup();
78         }
79         Entry entry = entryFor(key);
80         if (entry != null) {
81             return entry.val();
82         }
83         return null;
84     }
85 
put(String key, String val)86     synchronized void put(String key, String val) {
87         if (++queryCount >= queryOverflow) {
88             cleanup();
89         }
90         Entry entry = entryFor(key);
91         if (entry != null) {
92             entry.setTimestamp(System.currentTimeMillis());
93             entry.setVal(val);
94         } else {
95             map.put(key, new Entry(System.currentTimeMillis(), val));
96         }
97     }
98 
clear()99     synchronized void clear() {
100         map.clear();
101     }
102 
entryFor(String key)103     private Entry entryFor(String key) {
104         Entry entry = map.get(key);
105         if (entry != null) {
106             long delta = System.currentTimeMillis() - entry.timestamp();
107             if (delta < 0 || delta >= millisUntilExpiration) {
108                 map.remove(key);
109                 entry = null;
110             }
111         }
112         return entry;
113     }
114 
cleanup()115     private void cleanup() {
116         Set<String> keySet = map.keySet();
117         // Avoid ConcurrentModificationExceptions
118         String[] keys = new String[keySet.size()];
119         int i = 0;
120         for (String key: keySet) {
121             keys[i++] = key;
122         }
123         for (int j = 0; j < keys.length; j++) {
124             entryFor(keys[j]);
125         }
126         queryCount = 0;
127     }
128 }
129