1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
|
/*
* Copyright (c) 2008, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package com.sun.beans;
import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.util.Map;
import java.util.WeakHashMap;
/**
* A hashtable-based cache with weak keys and weak values.
* An entry in the map will be automatically removed
* when its key is no longer in the ordinary use.
* A value will be automatically removed as well
* when it is no longer in the ordinary use.
*
* @since 1.7
*
* @author Sergey A. Malenkov
*/
public final class WeakCache<K, V> {
private final Map<K, Reference<V>> map = new WeakHashMap<K, Reference<V>>();
/**
* Returns a value to which the specified {@code key} is mapped,
* or {@code null} if this map contains no mapping for the {@code key}.
*
* @param key the key whose associated value is returned
* @return a value to which the specified {@code key} is mapped
*/
public V get(K key) {
Reference<V> reference = this.map.get(key);
if (reference == null) {
return null;
}
V value = reference.get();
if (value == null) {
this.map.remove(key);
}
return value;
}
/**
* Associates the specified {@code value} with the specified {@code key}.
* Removes the mapping for the specified {@code key} from this cache
* if it is present and the specified {@code value} is {@code null}.
* If the cache previously contained a mapping for the {@code key},
* the old value is replaced by the specified {@code value}.
*
* @param key the key with which the specified value is associated
* @param value the value to be associated with the specified key
*/
public void put(K key, V value) {
if (value != null) {
this.map.put(key, new WeakReference<V>(value));
}
else {
this.map.remove(key);
}
}
/**
* Removes all of the mappings from this cache.
*/
public void clear() {
this.map.clear();
}
}
|
