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Tip of the Day
Language: Java
Expertise: Advanced
Feb 17, 2009

Developing a NIO-Based Client

This tip shows you how to develop a New I/O-based client. As you probably know, NIO offers many advantages such as speed and the ability to maintain a large number of concurrent connections. Here's the code:

import java.io.*;
import java.nio.*;
import java.net.*;
import java.util.*;
import java.nio.channels.*;
import java.nio.charset.*;

public class ClientNIO{
  public static void main(String args[])
  {
  InetSocketAddress ISA=null;
  SocketChannel clientNIO=null;
  Selector selector=null;
  SelectionKey key=null;
  
  int port=5000;
  
  try{
     clientNIO=SocketChannel.open();
     clientNIO.configureBlocking(false);     
     }catch(IOException e)
        {System.out.println(e.getMessage());}

 try{
    InetAddress addr=InetAddress.getByName("localhost");
    ISA=new InetSocketAddress(addr,port);           
    }catch(UnknownHostException e)
      {System.out.println(e.getMessage());}
     
 try{
    clientNIO.connect(ISA); 
    }catch(IOException e)
      {System.out.println(getMessage());}
    
  try{
     selector = Selector.open(); 
     }catch(IOException e)
          {System.out.println(e.getMessage());}
     
  try{     
     SelectionKey clientKey=clientNIO.register(selector,SelectionKey.OP_CONNECT); 
     }catch(Exception e)        
        {System.out.println(e.getMessage());}
           
  try{      
      while(selector.select(1000)>0)
             {                          
             Set keys=selector.selectedKeys();
             Iterator iter=keys.iterator();
             while(iter.hasNext())
                  {
                  key=(SelectionKey)iter.next();
                  iter.remove();
                  SocketChannel channel=(SocketChannel)key.channel();
                  if((key.isValid())&&(key.isConnectable()))
                      {
                      if(channel.isConnectionPending())channel.finishConnect();
                      ByteBuffer serverBuf = null;
                      
                      System.out.println("Connected...");

                      while(true)
                           {
                           serverBuf = ByteBuffer.wrap(new String("Answer me dear server ...").getBytes());
                           channel.write(serverBuf);
                                                    
                           serverBuf.clear();
                       
                            ByteBuffer clientBuf = ByteBuffer.allocateDirect(1024);
                            clientBuf.clear();
                            channel.read(clientBuf);                                                   
                                        
                            clientBuf.flip(); 
                            Charset charset=Charset.forName("ISO-8859-1");
                            CharsetDecoder decoder = charset.newDecoder();
  
                            CharBuffer charBuffer = decoder.decode(clientBuf);
                            System.out.println(charBuffer.toString());
                            clientBuf.clear();                 
                            }     
                      }
                   }  
              }
     }catch(IOException e)
        {System.out.println(e.getMessage());
               try{
                  key.channel().close();key.cancel();
                  }catch(Exception ex)
                     {System.out.println(e.getMessage());}}

  }
Leonard Anghel
 
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