Java 数据包困惑

Question

我正在用 Java 编写服务器程序。这是我的主线程代码:

public class EntryThread extends Thread {

    volatile byte[] toSend;

    public EntryThread() {

    }

    public void TreatRequest(byte[] data, InetAddress IPAddress)
    {
        try {
            switch (data[0])
            {
                case 0: // ping
                    toSend = new byte[] { (byte) 255, data[1], (byte) 255};
                    Server.serverSocket.send(new DatagramPacket(toSend, 3, IPAddress, 17550));
                    break;
                case 2:
                    break;
            }
        } catch (Exception e)
        {
            System.out.println("Exception because of a packet malformation issue. You can ignore it.");
            e.printStackTrace();
        }
    }

    public void run() { 
        Runtime.getRuntime().addShutdownHook(new Thread(){public void run(){ 
            try {
                Server.serverSocket.close();
                System.out.println("The server is shut down!");
            } catch (Exception e) { /* failed */ }
        }});

        try {
            Server.serverSocket = new DatagramSocket(Configuration.port);

            byte[] receiveData = new byte[512];

            DatagramPacket receivePacket = new DatagramPacket(receiveData,
                               receiveData.length);
            while(true) {
                Server.serverSocket.receive(receivePacket);
                byte[] data = receivePacket.getData();
                System.out.println("RECEIVED: " + new String(data));
                InetAddress IPAddress = receivePacket.getAddress();

                /*
                 * data[0] : command/255 if 
                 * data[1] : C-ID.
                 * data[2] : arguments/content
                 */

                TreatRequest(data, IPAddress);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

一切看起来都不错，但是当我使用某些软件(PacketSender)发送数据包时，它开始变得奇怪。这是我的控制台:

RECEIVED: [][][][][][]... // I sent 00 in hex, no problem there)
RECEIVED: ÿ[]ÿ[][][][]... // here's the response of the server)
RECEIVED: [][]ÿ[][][][]... // this ÿ is still there even if I just sent 00 in hex.

因此它只会覆盖数组，我被迫将其变大。

所以我想知道:

• 如何使数据包日期每次都重置为很多 0？
• 我可以只获取数据包大小的数组，而不是这种奇怪的“将数组作为参数传递”方法吗？

Answer 1

每次接收到数据包时，DatagramPacket 使用的缓冲区不会被清除。但是，getLength() 方法会告诉您当前数据包中接收了多少数据，您应该使用它来限制从缓冲区中提取的数据。举个例子:

System.out.println("RECEIVED: " + new String(data,0,receivePacket.getLength()));