TCP（Transmission Control Protocol 传输控制协议）是一种面向连接的、可靠的、基于字节流的传输层通信协议.

面向连接：服务器创建一个连接端口，客户端去连接服务器实现通信。

可靠的：tcp协议是是在连接成功之后才会发送数据，而基于UDP的协议是事先不会征求对方意见，直接将数据传送出去，因此TCP协议传输中，数据更可靠，更安全。

基于字节流：tcp协议中传递的信息是以流的形式传递的，在java中可通过inputstream来捕获，通过outputstream发送。

对于接收数据的时候出现假死的状态：

readLine()函数读取一行，结尾需要"\n"才能结束，不然会一直卡死在这里，因此大家在用printwriter的时候要print一个"\n"，然后把printwriter flush掉。就不会假死了！

这样：pw.write("fuck you cient");    //send to server
           pw.write("\n");
           pw.flush();

在java中，tcp协议是已经封装好的类，可直接供用户使用。其中关键的两个类是

Socket类     ServerSocket类。

ServerSocket类用来创建服务器，具体用法请参照jdk文档。常用用法是

ServerSocket ss = new ServerSocket((int)port)     //传入一个端口号，用户自定

Socket用于控制两端的连接，服务器的Socket可以和客户端的Socket相连接：

socket可以使用inputstream和outputstream进行相互通信。

（服务器中通常是将已将建立连接的socket丢给子线程通信，但是点对点可以让服务器处理一个socket就行了，不需要再生成子线程进行通信交流）

代码分为三个文件。

程序运行结果：

以下是代码附上：

//package org.cat.Client;import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.Socket;public class MyClient {public static void main(String[] args){try {Socket s = new Socket("localhost", 12341);System.out.println("conneting to server successfully");//successfully connecting to server//Now sending some data to server//1.create outputStream and so on...OutputStream out = s.getOutputStream();PrintWriter pw = new  PrintWriter(out);pw.write("fuck you server");  //send to serverpw.write("\n");       //importantpw.flush();System.out.println("I have sended to server");//2.receiving data from serverInputStream in = s.getInputStream();InputStreamReader inReader = new InputStreamReader(in);BufferedReader bfdReader = new BufferedReader(inReader);String tmp = "xxxx,receiving failed";while((tmp = bfdReader.readLine()) != null)System.out.println("server tells:"+tmp);//close allin.close();inReader.close();bfdReader.close();out.close();pw.close();} catch (IOException e) {System.out.println("connecting failed,have u opened server?");e.printStackTrace();}}
}

//package org.cat.Server;import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;public class MyServer {public static void main(String[] args){try {@SuppressWarnings("resource")ServerSocket sers = new ServerSocket(12341);//then wait for client to connectSocket s;System.out.println("waiting for client to connect");s = sers.accept();new MyThread(s);} catch (IOException e) {System.out.println("set up server failed??");e.printStackTrace();}}}

//package org.cat.Server;import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.Socket;public //service for every client
class MyThread extends Thread{Socket s;public MyThread(Socket s) {this.s = s;start();//telling that connection has been settle up System.out.println("successed to connet with port of"+s.getLocalPort());//now receiving data and talk back to client//1.receivetry {InputStream in = s.getInputStream();InputStreamReader inReader = new InputStreamReader(in);BufferedReader bfdReader = new BufferedReader(inReader);String tmp = "xxxx,receiving failed";if((tmp = bfdReader.readLine()) != null)System.out.println("client tells:"+tmp);//anwser clientOutputStream out = s.getOutputStream();PrintWriter pw = new  PrintWriter(out);pw.write("fuck you cient");   //send to serverpw.write("\n");pw.flush();System.out.println("I have sended to client");//close allout.close();pw.close();in.close();inReader.close();bfdReader.close();} catch (IOException e1) {System.out.println("get inputStream from client failed");e1.printStackTrace();}System.out.println("now to shut connection");try {s.close();System.out.println("shut down connection successfully");} catch (IOException e) {System.out.println("shut server failed,have u opened it?");e.printStackTrace();}}}