Day 21：网络编程（2）

以课程中feiQ为例，feiQ作为一个典型的网络编程应用，用一段代码尝试给自己的发送消息

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class Demo1 {

    public static void main(String[] args) throws IOException {
        // 建立udp的服务
        DatagramSocket socket = new DatagramSocket();
        // 准备数据，把数据封装到数据包中
        String data = "feiQ你好！";
        DatagramPacket packet = new DatagramPacket(data.getBytes(),data.getBytes().length,InetAddress.getByName("192.168.1.101"), 2425);
        // 发送数据
        socket.send(packet);
        // 关闭资源
        socket.close();
    }
}

此代码在执行的时候是是失败的，在网络编程（1）中，运行的接收和发送方是成功的，为什么这里就不可以了呢？

原因： 每个网络程序都有自己所处理的特定格式数据,如果接收到的数据不符合指定的格式，那么就会被当成垃圾数据丢弃。(加密)

feiQ是局域网程序，所以可以随便尝试，QQ作为面向大众，尝试的话就会犯罪~hiahiahia~~不要玩火哟！

解决方法：

　　飞Q接收的数据格式：
 　　version:time :sender : ip: flag:content ;
　　 版本号：时间：发送人 :IP：发送的标识符(32): 真正的内容;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class Demo1 {

    public static void main(String[] args) throws IOException {
        // 建立udp的服务
        DatagramSocket socket = new DatagramSocket();
        // 准备数据，把数据封装到数据包中
        String data = getData("feiQ你好！");
        DatagramPacket packet = new DatagramPacket(data.getBytes(),data.getBytes().length,InetAddress.getByName("192.168.15.255"), 2425);
        // 发送数据
        socket.send(packet);
        // 关闭资源
        socket.close();
    }
    // 把数据拼接成指定格式的数据
    public static String getData(String content) {
        StringBuilder sb = new StringBuilder();
        sb.append("1.0:");
        sb.append(System.currentTimeMillis() + ":");
        sb.append("小号:");
        sb.append("192.168.10.1:");
        sb.append("32:");
        sb.append(content);
        return sb.toString();
    }
}

解决群发（一对多）问题只需修改为广播地址

在udp协议中，有一个IP地址称作为广播地址，广播地址就是主机号为255地址。给广播IP地址发送消息的时候，在同一个网络段的机器都可以接收 到信息。（192.168.15.255）

给send方法加一个死循环会特别嗨哟

群聊（多对多）：同时要发送和接收（多线程）

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;

//发送
public class Demo3 extends Thread {
    @Override
    public void run() {
        try {
            DatagramSocket socket = new DatagramSocket();
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            String line = null;
            DatagramPacket packet = null;
            while((line = reader.readLine())!=null) {
                packet = new DatagramPacket(line.getBytes(), line.getBytes().length, InetAddress.getByName("192.168.15.255"), 9090);
                socket.send(packet);
                socket.close();
            }
        } catch (SocketException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    
    }
}

//接收
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class Demo2 extends Thread {
    @Override
    public void run() {
    
            try {
                DatagramSocket socket = new DatagramSocket(9090);
                byte[] buf = new byte[1024];
                DatagramPacket packet = new DatagramPacket(buf, buf.length);
                boolean flag = true;
                while(flag) {
                    socket.receive(packet);
                    System.out.println(packet.getAddress().getHostAddress()+"说:"+new String(buf,0,packet.getLength()));
                }
                socket.close();
            } catch (SocketException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
    }
}

//启动多线程
public class Demo4 {
    public static void main(String[] args) {
        Demo3 receive = new Demo3();
        receive.start();
        
        Demo2 send = new Demo2();
        send.start();
    }
}

udp是一个不可靠（数据包可能会丢失的协议，什么情况下数据包会出现丢失呢？，并测试

1.带宽不足 。
2.cpu的处理能力不足。

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class Demo5 {
    
    public static void main(String[] args) throws Exception {
        //建立udp的服务
        DatagramSocket socket = new DatagramSocket();
        //准备数据，数据封装到数据中发送
        DatagramPacket packet = null;
        for(int i =  0 ; i< 10; i++){  //连续发送10个数据包，如果你家机子好网速好就加大数据量
            String data =i +"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
            packet = new DatagramPacket(data.getBytes(), data.getBytes().length, InetAddress.getLocalHost(), 9090);
            //发送数据包
            socket.send(packet);
        }
        //关闭资源
        socket.close();
    }
}

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class Demo6 {
    
    public static void main(String[] args) throws IOException, Exception {
        //建立udp的服务
        DatagramSocket socket = new DatagramSocket(9090);
        
        //建立空的数据包存储数据
        byte[] buf = new byte[1024];
        DatagramPacket packet = new DatagramPacket(buf, buf.length);
        
        //不断接收数据包
        while(true){
            socket.receive(packet);
            System.out.println(new String(buf,0,packet.getLength()));
            Thread.sleep(10);
        }    
    }
}

之所以上一段代码不关闭接收端socket是为了无限接收数据。