UDP 客户端服务器文件传输

Question

我正在尝试通过 UDP 将数据包从客户端发送到服务器。我面临的问题是，如果最后一个数据包的大小小于我们正在读取的字节数组的大小，那么来自前一个数据包的冗余数据就会被附加到它上面。我尝试只将最后一个数据包的正确部分复制到一个新的字节数组中，然后发送它，但客户端以某种方式只发送了错误的数据包。请任何人指出我做错了什么。提前致谢。

Client.java:

class client
{
static int serverPort;
static String filename;
    public static void main(String args[]) throws SocketException, IOException
    {
        int count=0;
        int MAX_SIZE = 1048;

        DatagramSocket clientSocket = new DatagramSocket();
        InetAddress IpAddress = InetAddress.getByName("localhost");

        byte[] sendData = new byte[MAX_SIZE];

        String filePath = "C:\\in.txt";
        File file = new File(filePath);
        FileInputStream fis = new FileInputStream(file);


        int totLength = 0; 

        while((count = fis.read(sendData)) != -1)    //calculate total length of file
        {
            totLength += count;
        }

        System.out.println("Total Length :" + totLength);

        int noOfPackets = totLength/MAX_SIZE;
        System.out.println("No of packets : " + noOfPackets);

        int off = noOfPackets * MAX_SIZE;  //calculate offset. it total length of file is 1048 and array size is 1000 den starting position of last packet is 1001. this value is stored in off.

        int lastPackLen = totLength - off;
        System.out.println("\nLast packet Length : " + lastPackLen);

        byte[] lastPack = new byte[lastPackLen-1];  //create new array without redundant information


        fis.close();

        FileInputStream fis1 = new FileInputStream(file);
        //while((count = fis1.read(sendData)) != -1 && (noOfPackets!=0))
        while((count = fis1.read(sendData)) != -1 )
        { 
            if(noOfPackets<=0)
                break;
            System.out.println(new String(sendData));
            DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IpAddress, 9876);
            clientSocket.send(sendPacket);
            System.out.println("========");
            System.out.println("last pack sent" + sendPacket);
        noOfPackets--;
        }

        //check
        System.out.println("\nlast packet\n");
        System.out.println(new String(sendData));

        lastPack = Arrays.copyOf(sendData, lastPackLen);

        System.out.println("\nActual last packet\n");
        System.out.println(new String(lastPack));
                //send the correct packet now. but this packet is not being send. 
        DatagramPacket sendPacket1 = new DatagramPacket(lastPack, lastPack.length, IpAddress,     9876);
        clientSocket.send(sendPacket1);
        System.out.println("last pack sent" + sendPacket1);

    }
}

Server.java:
import java.io.*;
import java.net.*;

class server
{
    public static void main(String args[]) throws IOException
    {
        DatagramSocket serverSocket = new DatagramSocket(9876);
        byte[] recData = new byte[1024];
        int i =0;

        FileWriter file = new FileWriter("C:\\Users\\ayushi\\Documents\\Semester 2\\Misc\\setups\\eclipse\\ip_1\\ip_second\\src\\out.txt");
        PrintWriter out = new PrintWriter(file);


        //BufferedOutputStream bos = new BufferedOutputStream(fos);

        while(true)
        {
            //PrintWriter out = new PrintWriter(file);

            DatagramPacket recPacket = new DatagramPacket(recData, recData.length);
            serverSocket.receive(recPacket);
            String line = new String(recPacket.getData());
            System.out.println("\n Data: " + line);
            out.println(line);
            System.out.println("\nPacket" + ++i + " written to file\n");
            out.flush();
        }
    }
}

Answer 1

如果最后一个数据包的大小小于我们正在读取的字节数组的大小，那么来自前一个数据包的冗余数据将被附加到它。

没有。问题是来自第一个数据包的字节仍然包含在recData 字节数组中。随后的读取将用第二个数据包的内容覆盖字节数组的开头，但数组的其余部分仍由第一个数据包中的数据填充。

根本问题是您忽略了实际接收的字节数。您还应该使用FileOutputStream，而不是Writer。试试这个：

class Server
{
    public static void main(String args[]) throws IOException
    {
        ...

        while(true)
        {
            DatagramPacket recPacket = new DatagramPacket(recData, recData.length);
            serverSocket.receive(recPacket);
            System.out.println("\n Packet length: " + recPacket.getLength());
            out.write((recPacket.getData(), 0, recPacket.getLength());
            System.out.println("\nPacket" + ++i + " written to file\n");
            out.flush();
        }
    }
}