3.UDP协议

发送Send

• 创建DatagramSocket, 随机端口号,也可以指定端口号
• 创建DatagramPacket, 指定数据, 长度, 地址, 端口
• 使用DatagramSocket发送DatagramPacket

• 关闭DatagramSocket

  接收Receive

• 创建DatagramSocket, 指定端口号

• 创建DatagramPacket, 指定数组, 长度
• 使用DatagramSocket接收DatagramPacket
• 关闭DatagramSocket

• 从DatagramPacket中获取数据

  接收方获取ip和端口号

• String ip = packet.getAddress().getHostAddress();

• int port = packet.getPort();

  UDP传输

  ```java package cn.giteasy.socket;

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

/*

• UDP传输之Send（发送） *
• 创建DatagramSocket, 随机端口号
• 创建DatagramPacket, 指定数据, 长度, 地址, 端口
• 使用DatagramSocket发送DatagramPacket
• 关闭DatagramSocket */ public class Demo01Send {

public static void main(String[] args) throws Exception {
    //要发送的数据
    String str = "how are you?";
    //接收消息的主机
    String host = "localhost";
    //接收数据的程序端口号
    int port = 8888;
    //创建Socket，使用随机端口，也可以构造方法中传入端口
    DatagramSocket socket = new DatagramSocket();
    //创建Packet,用于存放数据
    DatagramPacket packet =
            new DatagramPacket(str.getBytes(), str.getBytes().length, InetAddress.getByName(host), port);
    //发送
    socket.send(packet);
    //关闭socket
    socket.close();
}

}

```java
package cn.giteasy.socket;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
/**
 *    UDP传输之Receive（接收）
 *         创建DatagramSocket, 指定端口号
 *         创建DatagramPacket, 指定数组, 长度
 *         使用DatagramSocket接收DatagramPacket
 *         关闭DatagramSocket
 *         从DatagramPacket中获取数据
 */
public class Demo01Receive {
    public static void main(String[] args) throws Exception {

        //当前接收端程序监听的端口
        int port = 8888;

        //创建Socket相当于创建码头,需指定端口号用于接收数据
        DatagramSocket socket = new DatagramSocket(port);
        //创建Packet，存放接收到的数据
        DatagramPacket packet = new DatagramPacket(new byte[1024], 1024);

        //阻塞:接收数据
        socket.receive(packet);

        //从Packet中获取数据
        byte[] arr = packet.getData();
        //获取有效的字节个数
        int len = packet.getLength();
        System.out.println(new String(arr,0,len));
        socket.close();
    }

}

UDP传输优化

可不间断发送消息和接收消息

package cn.giteasy.socket;

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

/**
 * 可持续发送，用户输入的数据
 */
public class Demo02Send {


    public static void main(String[] args) throws Exception {
        String host = "localhost";
        int port = 8888;
        DatagramSocket socket = new DatagramSocket();

        Scanner scanner = new Scanner(System.in);

        while (true){
            String str = scanner.nextLine();
            if("exit".equals(str)){
                break;
            }

            DatagramPacket packet =
                    new DatagramPacket(str.getBytes(), str.getBytes().length, InetAddress.getByName(host), port);
            socket.send(packet);
        }

        socket.close();
    }

}

package cn.giteasy.socket;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

/**
 * 可持续接收发送端的消息
 */
public class Demo02Receive {

    public static void main(String[] args) throws Exception {
            int port = 8888;
            DatagramSocket socket = new DatagramSocket(port);
            DatagramPacket packet = new DatagramPacket(new byte[1024], 1024);
            while(true){
                socket.receive(packet);
                byte[] arr = packet.getData();
                int len = packet.getLength();
                String hostAddress = packet.getAddress().getHostAddress();
                int sendPort = packet.getPort();
                System.out.println(hostAddress+":" + sendPort + " => " +new String(arr,0,len));
            }
    }

}

UDP传输多线程

使用多线程实现:发送和接收在同一进程内进行

class Send extends Thread {

    private String host;
    private int port;

    Send(String host,int port){
        this.host = host;
        this.port = port;
    }



    @Override
    public void run() {
        try {
            DatagramSocket socket = new DatagramSocket();
            Scanner scanner = new Scanner(System.in);
            while (true){
                System.out.print(host + ":" + port + " <= 请输入要发送的消息：");
                String str = scanner.nextLine();
                if("exit".equals(str)){
                    break;
                }

                DatagramPacket packet =
                        new DatagramPacket(str.getBytes(), str.getBytes().length, InetAddress.getByName(host), port);
                socket.send(packet);

                try {
                    //等待接收端打印完成，最好的办法是使用线程间通信实现，wait 和 notify
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

            socket.close();
        }  catch (IOException e) {

            e.printStackTrace();
        }        
    }
}

class Receive extends Thread {

    private int port;

    Receive(int port){
        this.port = port;
    }
    @Override
    public void run() {
        try {

            DatagramSocket socket = new DatagramSocket(port);
            DatagramPacket packet = new DatagramPacket(new byte[1024], 1024);
            while(true){
                socket.receive(packet);
                byte[] arr = packet.getData();
                int len = packet.getLength();
                String hostAddress = packet.getAddress().getHostAddress();
                int sendPort = packet.getPort();
                System.out.println(hostAddress+":" + sendPort + " => " +new String(arr,0,len));
            }
        } catch (IOException e) {

            e.printStackTrace();
        }
    }
}

/**
 * 使用多线程实现:发送和接收在同一进程内进行
 */
public class Demo03SendAndReceive {


    public static void main(String[] args) {
        //接收端线程
        Receive receive = new Receive(8888);
        //发送端线程
        Send send = new Send("localhost", 8888);

        receive.start();
        send.start();

    }

}