java udp 心跳

Java中使用UDP实现心跳的方法如下：

1. 创建一个DatagramSocket对象，并指定监听的端口号。

2. 创建一个DatagramPacket对象，并指定发送的数据和目的地的地址和端口号。

3. 使用DatagramSocket的send()方法发送数据包。

4. 使用DatagramSocket的receive()方法接收数据包。

5. 在接收到数据包后，判断是否为心跳包。如果是心跳包，发送一个确认包给发送方。

6. 在发送方接收到确认包后，确认包的标记位设置为true。

7. 在发送心跳包之前，检查确认包的标记位是否为true，如果为true，则发送心跳包，否则重新发送确认包。

8. 设置定时器，定期发送心跳包。

下面是示例代码：

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.util.Timer;
import java.util.TimerTask;

public class UdpHeartbeat {
    private static final int PORT = 8888; // 监听的端口号
    private static final String HOSTNAME = "localhost"; // 目的地的地址
    private static final int INTERVAL = 5000; // 发送心跳包的时间间隔（毫秒）
    private static final int TIMEOUT = 10000; // 接收超时时间（毫秒）
    private static final byte[] HEARTBEAT_DATA = "heartbeat".getBytes(); // 心跳包的数据

    private DatagramSocket socket;
    private InetAddress address;
    private boolean confirmed = true; // 是否已经收到确认包

    public UdpHeartbeat() throws Exception {
        socket = new DatagramSocket(PORT);
        address = InetAddress.getByName(HOSTNAME);
        socket.setSoTimeout(TIMEOUT);
    }

    public void start() {
        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            public void run() {
                sendHeartbeat();
            }
        }, INTERVAL, INTERVAL);

        while (true) {
            receivePacket();
        }
    }

    private void sendHeartbeat() {
        if (confirmed) {
            // 发送心跳包
            DatagramPacket packet = new DatagramPacket(HEARTBEAT_DATA, HEARTBEAT_DATA.length, address, PORT);
            try {
                socket.send(packet);
                System.out.println("Sent heartbeat packet.");
            } catch (Exception e) {
                System.err.println("Failed to send heartbeat packet: " + e.getMessage());
            }
            confirmed = false;
        } else {
            // 发送确认包
            byte[] data = new byte[1024];
            DatagramPacket packet = new DatagramPacket(data, data.length);
            packet.setData("confirm".getBytes());
            packet.setAddress(address);
            packet.setPort(PORT);
            try {
                socket.send(packet);
                System.out.println("Sent confirm packet.");
            } catch (Exception e) {
                System.err.println("Failed to send confirm packet: " + e.getMessage());
            }
        }
    }

    private void receivePacket() {
        byte[] data = new byte[1024];
        DatagramPacket packet = new DatagramPacket(data, data.length);
        try {
            socket.receive(packet);
            System.out.println("Received packet from " + packet.getAddress().getHostAddress() + ":" + packet.getPort());
            if (isHeartbeatPacket(packet)) {
                sendConfirm(packet);
            } else if (isConfirmPacket(packet)) {
                confirmed = true;
            }
        } catch (Exception e) {
            // ignore
        }
    }

    private boolean isHeartbeatPacket(DatagramPacket packet) {
        return new String(packet.getData(), packet.getOffset(), packet.getLength()).equals(new String(HEARTBEAT_DATA));
    }

    private boolean isConfirmPacket(DatagramPacket packet) {
        return new String(packet.getData(), packet.getOffset(), packet.getLength()).equals("confirm");
    }

    private void sendConfirm(DatagramPacket packet) {
        byte[] data = new byte[1024];
        DatagramPacket confirmPacket = new DatagramPacket(data, data.length);
        confirmPacket.setData("confirm".getBytes());
        confirmPacket.setAddress(packet.getAddress());
        confirmPacket.setPort(packet.getPort());
        try {
            socket.send(confirmPacket);
            System.out.println("Sent confirm packet to " + packet.getAddress().getHostAddress() + ":" + packet.getPort());
        } catch (Exception e) {
            System.err.println("Failed to send confirm packet: " + e.getMessage());
        }
    }

    public static void main(String[] args) throws Exception {
        UdpHeartbeat heartbeat = new UdpHeartbeat();
        heartbeat.start();
    }
}

以上代码实现了一个简单的UDP心跳程序。在程序运行期间，会每隔一段时间发送一个心跳包，如果收到了心跳包，则发送一个确认包给发送方，如果在一定时间内没有收到确认包，则重新发送确认包。