HistoryQueue


1   /*
2   @COPYRIGHT@
3   */
4   package demo.jmx;
5   
6   import java.util.LinkedList  ;
7   import java.util.List  ;
8   
9   /**
10  * Bounded queue collection
11  */
12  public class HistoryQueue 
13  implements IHistory 
14  {
15     private static final int DEFAULT_INTERVAL = 30;
16  
17     private final long granularity;
18     private final int capacity;
19     private final List   buffer = new LinkedList  ();
20  
21     private boolean enabled = true;
22  
23     public HistoryQueue() 
24     {
25        this(DEFAULT_INTERVAL, 24 * 60 * 60 / DEFAULT_INTERVAL);  // default 24h
26     }
27  
28     public HistoryQueue(int granularity, int capacity) 
29     {
30        this.granularity = granularity * 1000;
31        this.capacity = capacity;
32     }
33  
34     // JMX access 
35  
36     public String  [] getHistory() 
37     {
38        synchronized(this.buffer) 
39        {
40           String  [] history = new String  [this.buffer.size()];
41           for(int i = 0; i<history.length; i++) 
42           {
43              HistoryData data = (HistoryData) this.buffer.get(i);
44              history[i] = data.toString();
45           }
46           return history;
47        }
48     }
49  
50     public boolean getEnabled() 
51     {
52        return this.enabled;
53     }
54  
55     public void setEnabled(boolean enabled) 
56     {
57        synchronized(this) 
58        {
59           this.enabled = enabled;
60        }
61     }
62  
63     public void reset() 
64     {
65        synchronized(this.buffer) 
66        {
67           this.buffer.clear();
68        }
69     }
70  
71     public void updateHistory(int duration, String   error) 
72     {
73        if(this.enabled) 
74        {
75           synchronized(this) 
76           {
77              HistoryData historyData = getHistoryData(System.currentTimeMillis());
78              historyData.update(duration, error);
79           }
80        }
81     }
82  
83     private HistoryData getHistoryData(long time) 
84     {
85        HistoryData data = (HistoryData) peek();
86  
87        long intervalStart = time - (time % granularity);
88  
89        if(data == null) 
90        {
91           data = new HistoryData(intervalStart, 0);
92           add(data);
93        } 
94        else 
95        {
96           if(time - data.getIntervalStart() > granularity) 
97           {
98              data = new HistoryData(intervalStart, 0);
99              add(data);
100          }
101       }
102       return data;
103    }
104 
105    /**
106    * Adds new object to the queue and returns object pushed out 
107    * of the queue as a result of add or null if nothing was 
108    * pushed out (max capacity not reached yet).
109    */
110    private Object   add(Object   o) 
111    {
112       Object   removed = null;
113       if(this.buffer.size() >= this.capacity) removed = this.buffer.remove(0);
114       this.buffer.add(o);
115       return removed;
116    }
117 
118    private Object   peek() 
119    {
120       final int size = this.buffer.size();
121       return size == 0 ? null : this.buffer.get(size - 1);
122    }
123 }
124
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