import java.io.*;

import java.net.*;

public class echoserver1

{ public static void main(string[] args )

{ try

{

serversocket s = new serversocket(8500);

socket incoming = s.accept( );

bufferedreader in = new bufferedreader

(new inputstreamreader(incoming.getinputstream()));

printwriter out = new printwriter

(incoming.getoutputstream(), true /* autoflush */);

out.println( "hello! enter bye to exit." );

boolean done = false;

while (!done)

{ string line = in.readline();

if (line == null) done = true;

else

{ out.println("echo: " + line);

if (line.trim().equals("bye"))

done = true;

}

}

incoming.close();

}

catch (exception e)

{ system.out.println(e);

}

}

}

// echoclient1.java

import java.io.*;

import java.net.*;

public class echoclient1 {      

 public static void main(string args[])   {

   try{                   

      if (args.length != 1){

         system.out.println("usage: java client servername");                           

         return;

      }  

      string  connectto= args[0];

      socket connection;

      // connect to server

      if(connectto.equals("localhost")){

         connection=new socket(inetaddress.getlocalhost(),8500);

      }

      else{

         connection=new socket(inetaddress.getbyname(connectto),8500);                                   

      }                   

      bufferedreader  input=new bufferedreader(new inputstreamreader(connection.getinputstream()));                       

      printwriter out = new printwriter(connection.getoutputstream(), true /* autoflush */);

      // read information from server                        

      string info;

      info = input.readline();

      system.out.println(info);

      boolean done = false;

      bufferedreader in = new bufferedreader(new inputstreamreader(system.in));

      string sinput;

      while(!done){

         sinput = in.readline();

         out.println(sinput);

         if (sinput.equalsignorecase("bye")) done = true;                           

         info = input.readline();                           

         system.out.println(info); 

     }

     connection.close();                                                               

   }

   catch(securityexception e){

     system.out.println("securityexception when connecting server!");          

   }             

   catch(ioexception e){

     system.out.println("ioexception when connecting server!");   

   }

 }

}

运行
1 运行服务器
java echoserver1
2 运行 客户端
java echoclient1 server_hostname