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
29package java.io;
30
31import java.util.Iterator;
32import java.util.Map;
33import java.util.LinkedHashMap;
34import java.util.Set;
35
36class 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}
128