SizedCacheEntry


1   package net.suberic.util.cache;
2   
3   /**
4    * This represents a cached object.  It stores the object itself, plus
5    * the size and last accessed time.
6    */
7   public class SizedCacheEntry {
8   
9     // the stored object itself.  note that this could be a reference to
10    // another object, or a source from which the object may be accessed.
11    protected Object   cachedValue;
12  
13    // the last accessed time
14    protected long lastAccessedTime;
15  
16    // the size that the cachedValue occupies in the cache.
17    protected long size = 0;
18  
19    /**
20     * Creates a new, empty SizedCacheEntry.
21     */
22    public SizedCacheEntry() {
23    }
24  
25    /**
26     * Creates a new SizedCacheEntry containing value which has been most
27     * recently accessed now.
28     */
29    public SizedCacheEntry(Object   value) {
30      cachedValue = value;
31      // yeah, whatever...
32      size = value.toString().length();
33      touchEntry();
34    }
35  
36    /**
37     * This gets the cached value.  Implementations may vary for this.
38     */
39    public Object   getCachedValue() {
40      return cachedValue;
41    }
42  
43    /**
44     * Deletes this entry.  Should be called in order to clean up entries
45     * for which simple removal from memory is insufficient.
46     *
47     * The default implementation does nothing; subclasses should override
48     * this method if cleanup is required.
49     */
50    public boolean removeFromCache() {
51      return true;
52    }
53  
54    /**
55     * Touches the SizedCacheEntry, making its last accessed time now.
56     */
57    public void touchEntry() {
58      lastAccessedTime = System.currentTimeMillis();
59    }
60  
61    /**
62     * Gets the size of this SizedCacheEntry.
63     */
64    public long getSize() {
65      return size;
66    }
67  
68    /**
69     * Gets the last accessed time for this entry.
70     */
71    public long getLastAccessedTime() {
72      return lastAccessedTime;
73    }
74  
75    /**
76     * Compares the underlying value for equality.
77     */
78    public boolean equals(Object   o) {
79      if (o != null) {
80        Object   testValue = null;
81        if (o instanceof SizedCacheEntry) {
82      testValue = ((SizedCacheEntry)o).getCachedValue();
83        } else {
84      testValue = o;
85        }
86        return o.equals(cachedValue);
87      }
88      
89      return (cachedValue == null);
90    }
91  }
92  
93
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