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1
21 package org.lobobrowser.util;
22
23 import java.util.*;
24
25
29 public class LRUCache implements java.io.Serializable  {
30 private static final long serialVersionUID = 940427225784212823L;
31 private final int approxMaxSize;
32 private final Map cacheMap = new HashMap();
33
34
37 private final TreeSet timedSet = new TreeSet();
38 private int currentSize = 0;
39
40 public LRUCache(int approxMaxSize) {
41 this.approxMaxSize = approxMaxSize;
42 }
43
44 public void put(Object key, Object value, int approxSize) {
45 if(approxSize > this.approxMaxSize) {
46 throw new IllegalArgumentException ("Max size is " + this.approxMaxSize);
47 }
48 OrderedValue ordVal = (OrderedValue) this.cacheMap.get(key);
49 if(ordVal != null) {
50 this.currentSize += (approxSize - ordVal.approximateSize);
51 this.timedSet.remove(ordVal);
52 ordVal.approximateSize = approxSize;
53 ordVal.value = value;
54 ordVal.touch();
55 this.timedSet.add(ordVal);
56 }
57 else {
58 ordVal = new OrderedValue(value, approxSize);
59 this.cacheMap.put(key, ordVal);
60 this.timedSet.add(ordVal);
61 this.currentSize += approxSize;
62 }
63 while(this.currentSize > this.approxMaxSize) {
64 this.removeLRU();
65 }
66 }
67
68 private void removeLRU() {
69 OrderedValue ordVal = (OrderedValue) this.timedSet.first();
70 if(ordVal != null) {
71 if(this.timedSet.remove(ordVal)) {
72 this.currentSize -= ordVal.approximateSize;
73 }
74 else {
75 throw new IllegalStateException ("Could not remove existing tree node.");
76 }
77 }
78 else {
79 throw new IllegalStateException ("Cannot remove LRU since the cache is empty.");
80 }
81 }
82
83 public Object get(Object key) {
84 OrderedValue ordVal = (OrderedValue) this.cacheMap.get(key);
85 if(ordVal != null) {
86 this.timedSet.remove(ordVal);
87 ordVal.touch();
88 this.timedSet.add(ordVal);
89 return ordVal.value;
90 }
91 else {
92 return null;
93 }
94 }
95
96 private class OrderedValue implements Comparable , java.io.Serializable {
97 private static final long serialVersionUID = 340227625744215821L;
98 private long timestamp;
99 private int approximateSize;
100 private Object value;
101
102 private OrderedValue(Object value, int approxSize) {
103 this.value = value;
104 this.approximateSize = approxSize;
105 this.touch();
106 }
107
108 private final void touch() {
109 this.timestamp = System.currentTimeMillis();
110 }
111
112 public int compareTo(Object arg0) {
113 if(this == arg0) {
114 return 0;
115 }
116 OrderedValue other = (OrderedValue) arg0;
117 long diff = this.timestamp - other.timestamp;
118 if(diff != 0) {
119 return (int) diff;
120 }
121 int hc1 = System.identityHashCode(this);
122 int hc2 = System.identityHashCode(other);
123 if(hc1 == hc2) {
124 hc1 = System.identityHashCode(this.value);
125 hc2 = System.identityHashCode(other.value);
126 }
127 return hc1 - hc2;
128 }
129 }
130 }
131 |
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