UDP客户端服务器文件传输

Question

我想通过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大小小于我们正在读取的字节数组的大小，那么来自先前数据包的冗余数据将被附加到它。我试着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发送错误的数据包。请任何人都可以指出我做错了什么。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所述字节阵列，其中我们正在阅读的大小，从先前分组然后冗余数据被附加到其上。

不是。问题是来自第一个数据包的字节仍包含在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然填充来自第一个数据包的数据。

潜在的问题是，您忽略了接收到的实际字节数。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(); 
     } 
    } 
}