java_udp编程

两个重要的类：

https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/net/DatagramPacket.html

https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/net/DatagramSocket.html

---

 简单示例：

package netProgram;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;

/**
 * 发送端
 * 1.使用DatagramSocket 指定端口 创建发送端
 * 2.准备数据  准成字节数组
 * 3.封装成 DatagramPacket,需要指定目的地
 * 4.发送包裹  send(DatagramPacket packet)
 * 5.释放资源
 * */
public class UDPTest2 {
    public static void main(String[] args) throws Exception {
        DatagramSocket client = new DatagramSocket(8888);//自身的端口号
        String data = "hello udp program!";
        byte[] datas = data.getBytes();
        //指定发往的目的地
        DatagramPacket packet = new DatagramPacket
                (datas, 0, datas.length, 
                        new InetSocketAddress("localhost", 9999));
        client.send(packet);
        client.close();
    }
}

package netProgram;

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

/**
 * 接收端
 * 1.使用DatagramSocket 指定端口 创建接收端
 * 2.准备容器  封装成DatagramPacket
 * 3.阻塞式接收 packet  receive(DatagramPacket packet)
 * 4.分析数据  byte[] getData()
 * 5.释放资源
 * */
public class UDPTest {
    public static void main(String[] args) throws Exception {
        DatagramSocket server = new DatagramSocket(9999);
        byte[] container = new byte[64*1024];
        DatagramPacket packet = new DatagramPacket(container, 0,container.length);
        server.receive(packet);
        
        byte[] data = packet.getData();
        System.out.println(new String(data));
        server.close();
    }
}

---

发送对象：关键是要转换成字节数组

package netProgram;

import java.io.ByteArrayInputStream;
import java.io.ObjectInputStream;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

/**
 * 接收端 1.使用DatagramSocket 指定端口 创建接收端 2.准备容器 封装成DatagramPacket 3.阻塞式接收 packet
 * receive(DatagramPacket packet) 4.分析数据 byte[] getData() 5.释放资源
 */
public class UDPTest {
    public static void main(String[] args) throws Exception {
        DatagramSocket server = new DatagramSocket(9999);
        byte[] container = new byte[64 * 1024];
        DatagramPacket packet = new DatagramPacket(container, 0, container.length);
        server.receive(packet);

        byte[] data = packet.getData();
        ByteArrayInputStream stream = new ByteArrayInputStream(data, 0, data.length);
        ObjectInputStream ois = new ObjectInputStream(stream);
        Person temp = (Person) ois.readObject();
        System.out.println(temp.getAge() + "--->" + temp.getName());
        server.close();
    }
}

package netProgram;

import java.io.ByteArrayOutputStream;
import java.io.ObjectOutputStream;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;

/**
 * 发送端
 * 1.使用DatagramSocket 指定端口 创建发送端
 * 2.准备数据  准成字节数组
 * 3.封装成 DatagramPacket,需要指定目的地
 * 4.发送包裹  send(DatagramPacket packet)
 * 5.释放资源
 * */
public class UDPTest2 {
    public static void main(String[] args) throws Exception {
        DatagramSocket client = new DatagramSocket(8888);//自身的端口号
        //String data = "hello udp program!";
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(stream);
        oos.writeObject(new Person(15, "john"));
        //byte[] datas = data.getBytes();
        byte[] datas = stream.toByteArray();
        //指定发往的目的地
        DatagramPacket packet = new DatagramPacket
                (datas, 0, datas.length, 
                        new InetSocketAddress("localhost", 9999));
        client.send(packet);
        client.close();
    }
}