使用线程池启动一个线程一直接收udp消息，使用java语言在jdk8的环境下编写

好的，以下是使用 Java 8 编写的示例代码：

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class UdpReceiver {
    private static final int PORT = 9999;
    private static final int BUFFER_SIZE = 1024;
    private static DatagramSocket socket;
    private static ExecutorService executor;

    public static void main(String[] args) throws IOException {
        // 创建DatagramSocket对象
        socket = new DatagramSocket(PORT);
        // 创建线程池，允许最多5个线程同时运行
        executor = Executors.newFixedThreadPool(5);

        System.out.println("UDP receiver started, listening on port " + PORT);

        while (true) {
            // 创建DatagramPacket对象，用于接收数据
            byte[] buffer = new byte[BUFFER_SIZE];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

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

            // 打印接收到的数据
            String message = new String(packet.getData(), 0, packet.getLength());
            InetAddress address = packet.getAddress();
            int port = packet.getPort();
            System.out.println("Received message from " + address + ":" + port + ": " + message);

            // 启动一个新线程来处理接收到的消息
            executor.execute(new UdpMessageHandler(address, port, message));
        }
    }

    private static class UdpMessageHandler implements Runnable {
        private final InetAddress address;
        private final int port;
        private final String message;

        public UdpMessageHandler(InetAddress address, int port, String message) {
            this.address = address;
            this.port = port;
            this.message = message;
        }

        @Override
        public void run() {
            // TODO: 处理接收到的UDP消息
        }
    }
}

这段代码中，我们创建了一个 `DatagramSocket` 对象并绑定了本地端口，然后创建了一个线程池，允许最多5个线程同时运行。接着进入一个无限循环，在循环中接收 UDP 消息并将其打印出来，然后启动一个新线程来处理接收到的消息。在 `UdpMessageHandler` 类中可以编写具体的消息处理逻辑。