Java NIO学习-UDP的例子

这几天需要实现一个底层基于UDP的协议，该协议底层使用UDP传输但是具有拥塞控制、超时重发、数据确认等功能又比TCP简单（RUDP，Reliable UDP）。在实现协议底层的UDP服务时准备使用Java的NIO，在网上查资料都是以TCP为例讲的，于是自己研究了一下基于UDP的NIO。

NIO的思路是基于多路选择的，即由原来的每个连接都由一个线程来等待消息，改为每个连接都在选择器上注册，由选择器来等待。当然NIO引入了很多新的概念，如Channel，Buffer、Charset、Selector等，使得编程更简洁、更面向对象化。

下面贴出用NIO API改造成UDP示例代码，注意其中使用Charset来编码解码的过程（当然Charset还支持很多其他编码不仅局限于默认编码）以及Buffer的使用。

 package  sinpo.usagedemo; 
 
 import  java.net.DatagramSocket; 
 import  java.net.InetSocketAddress; 
 import  java.net.SocketAddress; 
 import  java.nio.ByteBuffer; 
 import  java.nio.CharBuffer; 
 import  java.nio.channels.DatagramChannel; 
 import  java.nio.channels.SelectionKey; 
 import  java.nio.channels.Selector; 
 import  java.nio.charset.Charset; 
 import  java.util.Iterator; 
 import  java.util.Set; 
 
 /** 
 * @author 徐辛波([email protected]) Oct 19, 2008 
 */ 
 public class  UDPServer extends  Thread { 
 public  void  run () { 
 Selector selector = null ; 
 try  { 
 DatagramChannel channel = DatagramChannel.open () ; 
 DatagramSocket socket = channel.socket () ; 
 channel.configureBlocking ( false ) ; 
 socket.bind ( new  InetSocketAddress ( 5057 )) ; 
 
 selector = Selector.open () ; 
 channel.register ( selector, SelectionKey.OP_READ ) ; 
 } catch  ( Exception e ) { 
 e.printStackTrace () ; 
 } 
 
 ByteBuffer byteBuffer = ByteBuffer.allocate ( 65536 ) ; 
 while  ( true ) { 
 try  { 
 int  eventsCount = selector.select () ; 
 if  ( eventsCount > 0 ) { 
 Set selectedKeys = selector.selectedKeys () ; 
 Iterator iterator = selectedKeys.iterator () ; 
 while  ( iterator.hasNext ()) { 
 SelectionKey sk = ( SelectionKey ) iterator.next () ; 
 iterator.remove () ; 
 if  ( sk.isReadable ()) { 
 DatagramChannel datagramChannel = ( DatagramChannel ) sk 
 .channel () ; 
 SocketAddress sa = datagramChannel 
 .receive ( byteBuffer ) ; 
 byteBuffer.flip () ; 
 
 // 测试：通过将收到的ByteBuffer首先通过缺省的编码解码成CharBuffer 再输出 
 CharBuffer charBuffer = Charset.defaultCharset () 
 .decode ( byteBuffer ) ; 
 System.out.println ( "receive message:" 
 + charBuffer.toString ()) ; 
 byteBuffer.clear () ; 
 
 String echo = "This is the reply message from 服务器。" ; 
 ByteBuffer buffer = Charset.defaultCharset () 
 .encode ( echo ) ; 
 datagramChannel.write ( buffer ) ; 
 } 
 } 
 } 
 } catch  ( Exception e ) { 
 e.printStackTrace () ; 
 } 
 } 
 
 } 
 
 public static  void  main ( String [] args ) { 
 new  UDPServer () .start () ; 
 } 
 }

Client

 package  sinpo.usagedemo; 
 
 import  java.net.InetSocketAddress; 
 import  java.net.SocketAddress; 
 import  java.nio.ByteBuffer; 
 import  java.nio.channels.DatagramChannel; 
 import  java.nio.channels.SelectionKey; 
 import  java.nio.channels.Selector; 
 import  java.nio.charset.Charset; 
 import  java.util.Iterator; 
 import  java.util.Set; 
 
 /** 
   *  @author  徐辛波([email protected]) 
   * Oct 19, 2008 
   */ 
 public class  UDPClient  extends  Thread  { 
      public  void  run () { 
          DatagramChannel channel =  null ; 
          Selector selector =  null ; 
          try  { 
              channel = DatagramChannel.open () ; 
              channel.configureBlocking ( false ) ; 
              SocketAddress sa =  new  InetSocketAddress ( "localhost" ,  5057 ) ; 
              channel.connect ( sa ) ; 
          }  catch  ( Exception e ) { 
              e.printStackTrace () ; 
          } 
 
          try  { 
              selector = Selector.open () ; 
              channel.register ( selector, SelectionKey.OP_READ ) ; 
              channel.write ( Charset.defaultCharset () .encode ( "Tell me your time" )) ; 
          }  catch  ( Exception e ) { 
              e.printStackTrace () ; 
          } 
          
          ByteBuffer byteBuffer = ByteBuffer.allocate ( 100 ) ; 
          while  ( true ) { 
              try  { 
                  int  eventsCount = selector.select () ; 
                  if  ( eventsCount >  0 ) { 
                      Set selectedKeys = selector.selectedKeys () ; 
                      Iterator iterator = selectedKeys.iterator () ; 
                      while  ( iterator.hasNext ()) { 
                          SelectionKey sk =  ( SelectionKey )  iterator.next () ; 
                          iterator.remove () ; 
                          if  ( sk.isReadable ()) { 
                              DatagramChannel datagramChannel =  ( DatagramChannel )  sk 
                                      .channel () ; 
                              datagramChannel.read ( byteBuffer ) ; 
                              byteBuffer.flip () ; 
                              
                              //TODO 将报文转化为RUDP消息并调用RUDP协议处理器来处理 
                              
                              System.out.println ( Charset.defaultCharset () .decode ( 
                                      byteBuffer ) .toString ()) ; 
                              byteBuffer.clear () ; 
                              datagramChannel.write ( Charset.defaultCharset () 
                                      .encode ( "Tell me your time" )) ; 
                          } 
                      } 
                  } 
              }  catch  ( Exception e ) { 
                  e.printStackTrace () ; 
              } 
          } 
 
      } 
 }

Java NIO学习-UDP的例子

Java NIO学习-UDP的例子

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