java Socket通信，客户端与服务端相互发消息

1.通信过程

网络分为应用层，http、ssh、telnet就是属于这一类，建立在传输层的基础上、其实就是定义了各自的编码解码格式，分层如下：

2.Socket连接

上述通信都要先在传输层有建立连接的基础上才能完成，TCP通过三次握手建立连接：

Socket与http的区别可以看下这个：
https://www.cnblogs.com/meier1205/p/5971313.html
还有搜索：http下午茶

3.JAVA socket 客户端与服务端互发消息

实现结构图：

客户端和服务端分别通过俩个线程来完成发送消息和接受消息，此前需要等待客户端与服务器端建立连接，这个java程序都帮你写好了，接收后就可以发消息了：

3.1 服务端代码

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Scanner;


public  class  Server_Test extends Thread{
    ServerSocket server = null;
    Socket socket = null;
    public Server_Test(int port) {
        try {
            server = new ServerSocket(port);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Override
    public void run(){

        super.run();
        try{
            System.out.println("wait client connect...");
            socket = server.accept();
            new sendMessThread().start();//连接并返回socket后，再启用发送消息线程
            System.out.println(socket.getInetAddress().getHostAddress()+"SUCCESS TO CONNECT...");
            InputStream in = socket.getInputStream();
            int len = 0;
            byte[] buf = new byte[1024];
            while ((len=in.read(buf))!=-1){
                System.out.println("client saying: "+new String(buf,0,len));
            }

        }catch (IOException e){
            e.printStackTrace();
        }
    }


    class sendMessThread extends Thread{
        @Override
        public void run(){
            super.run();
            Scanner scanner=null;
            OutputStream out = null;
            try{
                if(socket != null){
                    scanner = new Scanner(System.in);
                    out = socket.getOutputStream();
                    String in = "";
                    do {
                        in = scanner.next();
                        out.write(("server saying: "+in).getBytes());
                        out.flush();//清空缓存区的内容
                    }while (!in.equals("q"));
                    scanner.close();
                    try{
                        out.close();
                    }catch (IOException e){
                        e.printStackTrace();
                    }
                }
            }catch (IOException e) {
                e.printStackTrace();
            }

        }

    }

    //函数入口
    public static void main(String[] args) {
        Server_Test server = new Server_Test(1234);
        server.start();
    }
}

3.2 客户端代码

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Scanner;

public class Client extends Thread {

    //定义一个Socket对象
    Socket socket = null;

    public Client(String host, int port) {
        try {
            //需要服务器的IP地址和端口号，才能获得正确的Socket对象
            socket = new Socket(host, port);
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    @Override
    public void run() {
        //客户端一连接就可以写数据个服务器了
        new sendMessThread().start();
        super.run();
        try {
            // 读Sock里面的数据
            InputStream s = socket.getInputStream();
            byte[] buf = new byte[1024];
            int len = 0;
            while ((len = s.read(buf)) != -1) {
                System.out.println(new String(buf, 0, len));
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //往Socket里面写数据，需要新开一个线程
    class sendMessThread extends Thread{
        @Override
        public void run() {
            super.run();
            //写操作
            Scanner scanner=null;
            OutputStream os= null;
            try {
                scanner=new Scanner(System.in);
                os= socket.getOutputStream();
                String in="";
                do {
                    in=scanner.next();
                    os.write((""+in).getBytes());
                    os.flush();
                } while (!in.equals("bye"));
            } catch (IOException e) {
                e.printStackTrace();
            }
            scanner.close();
            try {
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    //函数入口
    public static void main(String[] args) {
        //需要服务器的正确的IP地址和端口号
        Client clientTest=new Client("127.0.0.1", 1234);
        clientTest.start();
    }
}

输出：
服务器端：

wait client connect...
127.0.0.1SUCCESS TO CONNECT...
client saying: hi
i am server #服务端说得话
hi,client #服务端说得话
client saying: hi,server

客户端：

hi #客户端说得话
server saying: i
server saying: amserver saying: server
server saying: hi,client
hi,server #客户端说得话

参考：http://blog.csdn.net/wenzhi20102321/article/details/52620323
Java基础之网络编程知识点总结
http://blog.csdn.net/u011460827/article/details/41654257