StreamingGetStateEvent


1   package org.jgroups;
2      
3   import java.io.OutputStream  ;
4   
5   /**
6    * 
7    * Represents an event returned by <code>channel.receive()</code>, as a result 
8    * of another channel instance requesting a state from this channel. Other channel 
9    * has to invoke <code>channel.getState()</code> indicating intent of state 
10   * retrieval. 
11   * 
12   * <p>
13   * 
14   * Allows applications using a channel in a pull mode to receive 
15   * <code>StreamingGetStateEvent</code> event and thus provide state to requsting 
16   * channel instance. Channels have to be configured with 
17   * <code>STREAMING_STATE_TRANSFER</code> protocol rather than the default 
18   * <code>STATE_TRANSFER</code> protocol in order to receive this event 
19   *  
20   * <p>
21   * 
22   * The following code demonstrates how to pull events from a channel, processing 
23   * <code>StreamingGetStateEvent</code> and sending hypothetical state through 
24   * <code>OutputStream</code> reference.
25   * 
26   * <blockquote><pre>
27   *  Object obj=channel.receive(0);
28   *  if(obj instanceof StreamingGetStateEvent) {
29   *      StreamingGetStateEvent evt=(StreamingGetStateEvent)obj;
30   *      OutputStream oos = null;
31   *      try {           
32   *          oos = new ObjectOutputStream(evt.getArg());         
33   *          oos.writeObject(state);   
34   *          oos.flush();
35   *      } catch (Exception e) {} 
36   *      finally
37   *      {
38   *          try {               
39   *              oos.close();
40   *          } catch (IOException e) {
41   *              System.err.println(e);
42   *          }
43   *      }                
44   *   }
45   * </pre></blockquote>
46   * 
47   * 
48   * @author Vladimir Blagojevic
49   * @see org.jgroups.JChannel#getState(Address, long)
50   * @see org.jgroups.StreamingMessageListener#getState(OutputStream)
51   * @since 2.4
52   * 
53   */
54  
55  public class StreamingGetStateEvent {
56  
57      OutputStream   os;
58      String   state_id;
59      
60      public StreamingGetStateEvent(OutputStream   os,String   state_id) {
61          super();
62          this.os=os;
63          this.state_id=state_id;
64      }
65      /**
66       * Returns OutputStream used for writing of a state.
67       * 
68       * @return the OutputStream
69       */
70      public OutputStream   getArg()
71      {
72          return os;
73      }
74      
75      /**
76       * Returns id of the partial state if partial state was requested. 
77       * If full state transfer was requested this method will return null.
78       * 
79       * @see JChannel#getState(Address, long)
80       * @see JChannel#getState(Address, String, long)
81       * @return partial state id 
82       */
83      public String   getStateId()
84      {
85          return state_id;
86      }   
87  
88  }
89
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