写一段代码用Java socket编程完整实现分类地址下，IP分组转发过程

以下是一个使用Java Socket编程实现分类地址下，IP分组转发过程的简单示例代码：

import java.net.*;
import java.io.*;

public class IPForwarder {
    public static void main(String[] args) throws IOException {
        // 创建接收套接字并绑定到本地IP地址和端口
        DatagramSocket receiveSocket = new DatagramSocket(8000, InetAddress.getLocalHost());

        // 创建发送套接字
        DatagramSocket sendSocket = new DatagramSocket();

        // 接收分组并转发
        while (true) {
            // 创建接收缓冲区并接收分组
            byte[] receiveData = new byte[1024];
            DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
            receiveSocket.receive(receivePacket);

            // 解析接收到的IP地址和端口号
            InetAddress destAddress = receivePacket.getAddress();
            int destPort = receivePacket.getPort();

            // 判断分类地址并转发
            byte[] data = receivePacket.getData();
            int addrType = (data[0] & 0xff) >> 6; // 获取分类地址类型
            switch (addrType) {
                case 0: // A类地址
                    InetAddress destA = InetAddress.getByAddress(new byte[]{data[1], data[2], data[3], data[4]});
                    DatagramPacket packetA = new DatagramPacket(data, data.length, destA, destPort);
                    sendSocket.send(packetA);
                    break;
                case 1: // B类地址
                    InetAddress destB = InetAddress.getByAddress(new byte[]{data[1], data[2], data[3], data[4]});
                    DatagramPacket packetB = new DatagramPacket(data, data.length, destB, destPort);
                    sendSocket.send(packetB);
                    break;
                case 2: // C类地址
                    InetAddress destC = InetAddress.getByAddress(new byte[]{data[1], data[2], data[3], data[4]});
                    DatagramPacket packetC = new DatagramPacket(data, data.length, destC, destPort);
                    sendSocket.send(packetC);
                    break;
                default: // 未知地址类型
                    System.err.println("Unknown address type: " + addrType);
            }
        }
    }
}

这个程序使用两个DatagramSocket对象实现接收和转发功能，首先创建一个接收套接字并绑定到本地IP地址和端口号8000，然后创建一个发送套接字。在主循环中，程序不断接收分组并解析分类地址，然后根据不同的地址类型转发分组。注意，这个示例代码只处理A、B、C三类地址，对于其他地址类型没有处理。