Server:

package Bosung;

import java.io.*;

import java.lang.*;

import java.net.ServerSocket;

import java.net.Socket;

public class Bosung {

    public static String nhap() throws IOException{

    String s;

    DataInputStream st=new DataInputStream(System.in);

    s=st.readLine();

    return s;

    }

    public static void main(String[] arg) {

        String ch,s;

        while(true){

    try{

    ServerSocket server=new ServerSocket(1234);

    Socket client=server.accept();

    DataInputStream is=new DataInputStream(client.getInputStream());

    DataOutputStream os=new DataOutputStream(client.getOutputStream());

    System.out.println("server: ");

    s=nhap();

    os.writeUTF(s);

    ch=is.readUTF();

    System.out.println("client: "+ch);

     }catch (IOException e){}

    }}

}

Client:

package Bosung;

import java.io.*;

import java.net.*;

import java.lang.*;

public class Bosung_client {

    public static String nhap(){

        String st = null;

        try{

        DataInputStream s=new DataInputStream(System.in);

        st=s.readLine();

       }catch (IOException e) {}

        return st;

    }

public static void main(String[] arg){

    String a,b;

while(true){

try{

    Socket client=new Socket("127.0.0.1",1234);

    DataInputStream is=new DataInputStream(client.getInputStream());

    DataOutputStream os=new DataOutputStream(client.getOutputStream());

    System.out.print("client:  ");

    b = nhap();

    System.out.println();

    //System.out.print(b);

    os.writeUTF("client1: "+b); 

    a=is.readUTF();

    System.out.print("server:"+a);

    System.out.println();  

}catch (IOException e){}

}}

}