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。

巴特西

Day 21：网络编程（2）

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