EchoClient.java

import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.IOException; import java.io.InputStreamReader; import java.io.OutputStreamWriter; import java.io.PrintWriter; import java.net.Socket; import java.net.UnknownHostException; public class EchoClient {
   public static void main(String args[]){
           String hostname = "localhost"; if(args.length > 0){
               hostname = args[0];         } //定义一系列的变量         PrintWriter  out = null;   //用于向网络写数据         BufferedReader in = null;  //用于向网络读数据         Socket socket = null;         BufferedReader userIn = null; //用于获取键盘输入         try {
   //实例化相应的变量             socket = new Socket(hostname,9998);                in = new BufferedReader(new InputStreamReader(socket.getInputStream()));             out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())),true);             userIn = new BufferedReader(new InputStreamReader(System.in));             System.out.println("connect to echo Server" + hostname); while(true){
                   String theLine = userIn.readLine(); if(theLine.equals(".")){
   break;                 }                 out.println(theLine);                 System.out.println(in.readLine());             }         } catch (UnknownHostException e) {
   // TODO Auto-generated catch block             e.printStackTrace();         } catch (IOException e) {
   // TODO Auto-generated catch block             e.printStackTrace();         } try {
               in.close();             socket.close();         } catch (IOException e) {
   // TODO Auto-generated catch block             e.printStackTrace();         }         out.close();     } }

EchoServer.java 

import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.IOException; import java.io.InputStreamReader; import java.io.OutputStreamWriter; import java.io.PrintWriter; import java.net.ServerSocket; import java.net.Socket; public class EchoServer {
       @SuppressWarnings("null") public static void main(String args[]){
   //首先定义四个变量         ServerSocket serversocket = null; //用于创建TCP服务器         Socket socket = null;             //用于获得连接套接字         BufferedReader in = null;   //用于接收数据         PrintWriter out = null;           //用于发送数据 //在网络编程中读取和发送相应的网络数据都需要自己的IO变量         try {
               serversocket = new ServerSocket(9998);   //实例化监听套接字,绑定端口9998             while(true){        //打印帮助消息 //这里将会打印IP地址和端口相关的信息                 System.out.println("The Server is start:" +serversocket); //等待客户端连接,连接成功之后,返回一个socket类型的变量,所有的数据传输都是和socket进行.                    socket = serversocket.accept(); //打印客户端的相关消息                 System.out.println("Accept the Client:" + socket); //实例化BufferedReader 对象用于接收客户端发送来的消息 //InputStreamReader的作用是将字节流转换成为字符流 //从网络中得到的数据将会存放在inBuffer变量当中                 in = new BufferedReader(new InputStreamReader(socket.getInputStream())); //得到输出流                 out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())),true); //通过上面的工作,我对网络的读写操作都准备好了                 while(true){
                       String instr  = in.readLine(); //按行读取数据     if(instr == null){
   break; //当客户端关闭时跳出循环                     }                     System.out.println("In server received the info:" + instr);//打印获得的数据                     out.println(instr);//将从网络中得到的数据回写                 }             }         } catch (IOException e) {
   // TODO Auto-generated catch block             e.printStackTrace();         } try {
               socket.close();             serversocket.close();             in.close();         } catch (IOException e) {
   // TODO Auto-generated catch block             e.printStackTrace();         }         out.close();         System.out.println("Server is exit");     } }