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1
5
6
9
10 package java.io;
11
12 import java.util.Iterator  ;
13 import java.util.Map ;
14 import java.util.LinkedHashMap ;
15 import java.util.Set ;
16
17 class ExpiringCache {
18 private long millisUntilExpiration;
19 private Map map;
20 private int queryCount;
22 private int queryOverflow = 300;
23 private int MAX_ENTRIES = 200;
24
25 static class Entry {
26 private long timestamp;
27 private String val;
28
29 Entry(long timestamp, String val) {
30 this.timestamp = timestamp;
31 this.val = val;
32 }
33
34 long timestamp() { return timestamp; }
35 void setTimestamp(long timestamp) { this.timestamp = timestamp; }
36
37 String val() { return val; }
38 void setVal(String val) { this.val = val; }
39 }
40
41 ExpiringCache() {
42 this(30000);
43 }
44
45 ExpiringCache(long millisUntilExpiration) {
46 this.millisUntilExpiration = millisUntilExpiration;
47 map = new LinkedHashMap () {
48 protected boolean removeEldestEntry(Map.Entry eldest) {
49 return size() > MAX_ENTRIES;
50 }
51 };
52 }
53
54 synchronized String get(String key) {
55 if (++queryCount >= queryOverflow) {
56 cleanup();
57 }
58 Entry entry = entryFor(key);
59 if (entry != null) {
60 return entry.val();
61 }
62 return null;
63 }
64
65 synchronized void put(String key, String val) {
66 if (++queryCount >= queryOverflow) {
67 cleanup();
68 }
69 Entry entry = entryFor(key);
70 if (entry != null) {
71 entry.setTimestamp(System.currentTimeMillis());
72 entry.setVal(val);
73 } else {
74 map.put(key, new Entry(System.currentTimeMillis(), val));
75 }
76 }
77
78 synchronized void clear() {
79 map.clear();
80 }
81
82 private Entry entryFor(String key) {
83 Entry entry = (Entry) map.get(key);
84 if (entry != null) {
85 long delta = System.currentTimeMillis() - entry.timestamp();
86 if (delta < 0 || delta >= millisUntilExpiration) {
87 map.remove(key);
88 entry = null;
89 }
90 }
91 return entry;
92 }
93
94 private void cleanup() {
95 Set keySet = map.keySet();
96 String [] keys = new String [keySet.size()];
98 int i = 0;
99 for (Iterator iter = keySet.iterator(); iter.hasNext(); ) {
100 String key = (String ) iter.next();
101 keys[i++] = key;
102 }
103 for (int j = 0; j < keys.length; j++) {
104 entryFor(keys[j]);
105 }
106 queryCount = 0;
107 }
108 }
109
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Java API By Example, From Geeks To Geeks.