smack 源码分析- PacketWriter (android上实现长连接)2

野性酷女 2022-08-08 05:29 137阅读 0赞

上一篇smack 源码分析一(android上实现长连接) 整体分析了smack长连接的流程, 本篇将详细介绍PacketWriter.

PacketWriter是在上篇在介绍initConnection()方法中创建的,那么详细看下PacketWriter的实现:

**\[java\]** [view plain][] [copy][view plain]

1.  **protected** PacketWriter(XMPPConnection connection) \{ 
2.  **this**.queue = **new** ArrayBlockingQueue<Packet>(500, **true**); 
3.  **this**.connection = connection; 
4.   init(); 
5.   \} 
6.  
7.  
8.  
9.  
10. **protected****void** init() \{ 
11. **this**.writer = connection.writer; 
12.  done = **false**; 
13.  lastActive = System.currentTimeMillis(); 
14. 
15. //开辟一个写网络流数据线程
16.  writerThread = **new** Thread() \{ 
17. **public****void** run() \{ 
18.  writePackets(**this**); 
19.  \} 
20.  \}; 
21. 
22.  writerThread.setName("Smack Packet Writer (" \+ connection.connectionCounterValue + ")"); 
23.  writerThread.setDaemon(**true**); 
24. 
25.  \} 
26. 
27. 
28. 
29. /\*\*
30.  \* 向网络流写数据包
31.  \* @param thisThread
32.  \*/
33. **private****void** writePackets(Thread thisThread) \{ 
34. **try** \{ 
35. // Open the stream.
36.  openStream(); 
37. // Write out packets from the queue.
38. **while** (!done && (writerThread == thisThread)) \{ 
39.  Packet packet = nextPacket(); 
40. **if** (packet != **null**) \{ 
41. **synchronized** (writer) \{ 
42.  writer.write(packet.toXML()); 
43.  writer.flush(); 
44. // Keep track of the last time a stanza was sent to the
45. // server
46.  lastActive = System.currentTimeMillis(); 
47.  \} 
48.  \} 
49.  \} 
50. 
51. **synchronized** (writer) \{ 
52. **while** (!queue.isEmpty()) \{ 
53.  Packet packet = queue.remove(); 
54.  writer.write(packet.toXML()); 
55.  \} 
56.  writer.flush(); 
57.  \} 
58. 
59.  queue.clear(); 
60.  writer.write("</stream:stream>"); 
61.  writer.flush(); 
62. 
63.  \} **catch** (IOException ioe) \{ 
64. **if** (!done) \{ 
65.  done = **true**; 
66.  connection.packetReader.notifyConnectionError(ioe); 
67.  \} 
68.  \} **finally** \{ 
69. **try** \{ 
70. **if** (writer != **null**) \{ 
71.  writer.close(); 
72.  \} 
73.  \} **catch** (Exception e) \{ 
74.  \} 
75.  \} 
76.  \}

在PacketWriter构造方法中传递参数XMPPConnection作为PacketWriter成员变量, 然后调用init()方法 ,而在init()方法中, 开辟一个线程专门用于向服务器写数据. writerPackets()里面是一个无限循环体, 不断的从消息队列queue读取pakcet消息读取完之后调用wirter.flush()方法, 将消息发送的服务器. 这个过程就完成了终端完服务器发送消息的过程.

接下来是, 终端如何与云端保持连接呢, 那肯定是发送心跳包咯. 我们来看下PacketWriter是如何发送心跳包的:

**\[java\]** [view plain][] [copy][view plain]

1.  /\*\*
2.   \* A TimerTask that keeps connections to the server alive by sending a space
3.   \* character on an interval.
4.   \*/
5.  **private****class** KeepAliveTask **implements** Runnable \{ 
6.  
7.  **private****int** delay; 
8.  **private** Thread thread; 
9.  
10. **public** KeepAliveTask(**int** delay) \{ 
11. **this**.delay = delay; 
12.  \} 
13. 
14. **protected****void** setThread(Thread thread) \{ 
15. **this**.thread = thread; 
16.  \} 
17. 
18. **public****void** run() \{ 
19. **try** \{ 
20. // Sleep 15 seconds before sending first heartbeat. This will give time to
21. // properly finish TLS negotiation and then start sending heartbeats.
22.  Thread.sleep(15000); 
23.  \} 
24. **catch** (InterruptedException ie) \{ 
25. // Do nothing
26.  \} 
27. **while** (!done && keepAliveThread == thread) \{ 
28. **synchronized** (writer) \{ 
29. // Send heartbeat if no packet has been sent to the server for a given time
30. **if** (System.currentTimeMillis() - lastActive >= delay) \{ 
31. **try** \{ 
32.  writer.write(" "); 
33.  writer.flush(); 
34.  \} 
35. **catch** (Exception e) \{ 
36. // Do nothing
37.  \} 
38.  \} 
39.  \} 
40. **try** \{ 
41. // Sleep until we should write the next keep-alive.
42.  Thread.sleep(delay); 
43.  \} 
44. **catch** (InterruptedException ie) \{ 
45. // Do nothing
46.  \} 
47.  \} 
48.  \} 
49.  \}

心跳发送类: KeepAliveTask 是一个自定义线程, 它定义了心跳发送的时间间隔, 在其run方法里面一个无限循环体每隔delay毫秒就向云端发发送一个空消息(当然, 如需要你可以根据项目需求自定义一个心跳包). 整个PacketWriter介绍基本到此结束, 在你应用登陆成功之后就可以开启KeepAliveTask 线程定时发送心跳包到服务器保持终端与服务器的长连接.

[view plain]: http://blog.csdn.net/wqhjfree/article/details/7194416#