使用Java在UDP基础上应用层实现可靠数据传输，并写出详细代码

好的，我会尽力回答。首先需要说明的是，UDP本身是不可靠的传输协议，因此在应用层实现可靠数据传输需要进行一定的处理。这里提供一种基于停止等待协议的实现方式，即发送方发送数据后等待接收方的确认，接收方收到数据后发送确认，发送方接收到确认后再发送下一个数据。以下是详细代码：

发送方代码：

import java.net.*;

public class Sender {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket();
        InetAddress address = InetAddress.getByName("127.0.0.1");
        int port = 8888;
        byte[] data = "Hello World".getBytes();
        int seq = 0;
        boolean acked = false;
        DatagramPacket packet = new DatagramPacket(data, data.length, address, port);
        while (!acked) {
            byte[] ackData = new byte[1];
            DatagramPacket ackPacket = new DatagramPacket(ackData, ackData.length);
            socket.send(packet);
            System.out.println("Send data: " + new String(data));
            socket.setSoTimeout(3000);
            try {
                socket.receive(ackPacket);
                int ackSeq = ackData[0];
                if (ackSeq == seq) {
                    System.out.println("Received ack: " + ackSeq);
                    acked = true;
                    seq++;
                }
            } catch (SocketTimeoutException e) {
                System.out.println("Timeout, resend data");
            }
        }
        socket.close();
    }
}

接收方代码：

import java.net.*;

public class Receiver {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket(8888);
        byte[] data = new byte[1024];
        int seq = 0;
        while (true) {
            DatagramPacket packet = new DatagramPacket(data, data.length);
            socket.receive(packet);
            String content = new String(packet.getData(), 0, packet.getLength());
            System.out.println("Received data: " + content);
            byte[] ackData = new byte[1];
            ackData[0] = (byte) seq;
            DatagramPacket ackPacket = new DatagramPacket(ackData, ackData.length, packet.getAddress(), packet.getPort());
            socket.send(ackPacket);
            System.out.println("Send ack: " + seq);
            seq++;
        }
    }
}

需要注意的是，这种实现方式只适用于数据量较小、网络环境较好的场景。如果需要应对更复杂的情况，需要进行更加高级的处理，比如拥塞控制、流量控制等。