Java -FTP程序在传输过程中损坏文件

Question

我已经使用插座制作了一个基本的客户端服务器FTP程序，但是由于某些原因，文件在传输过程中被损坏。在下面的情况下，我将文件从客户端推向服务器。它几乎有效，因为某些文件（例如.png）传输并打开罚款，但其他文件（.docx）却没有。我传输的任何文件与我发送的文件不同。

客户端代码：

File file = null;
            FTPDataBlock transferBlock;
            int numBytesRead = 0;
            int blockNumber = 1;
            int blockSize = 1024;
            byte[] block = new byte[blockSize];
            fc = new JFileChooser();
            // select file to upload
            int returnVal = fc.showOpenDialog(Client.this);
            if (returnVal == JFileChooser.APPROVE_OPTION) {
                file = fc.getSelectedFile();
                try {
                    // get total number of blocks and send to server
                    int totalNumBlocks = (int)Math.ceil((file.length()*1.0) / blockSize);
                    System.out.println("File length is: " + file.length());
                    FTPCommand c = new FTPCommand("PUSH", Integer.toString(totalNumBlocks));
                    oos = new ObjectOutputStream(sock.getOutputStream());
                    oos.writeObject(c);
                    oos.flush();
                    // send to server block by block
                    FileInputStream fin = new FileInputStream(file);
                    while ((numBytesRead = fin.read(block)) != -1){
                        transferBlock = new FTPDataBlock(file.getName(), blockNumber, block);
                        blockNumber++;
                        System.out.println("Sending block " + transferBlock.getBlockNumber() + " of " + totalNumBlocks);
                        oos = new ObjectOutputStream(sock.getOutputStream());
                        oos.writeObject(transferBlock);
                        oos.flush();
                    }
                    fin.close();
                    System.out.println("PUSH Complete");
                    // get response from server
                    ois = new ObjectInputStream(sock.getInputStream());
                    FTPResponse response = (FTPResponse)ois.readObject();
                    statusArea.setText(response.getResponse());

                } catch (IOException | ClassNotFoundException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            }

服务器代码：

else if (cmd.getCommand().equals("PUSH")){
                    // get total number of file blocks
                    int totalNumBlocks = Integer.parseInt(cmd.getParameters());
                    // get first block
                    in = new ObjectInputStream(sock.getInputStream());
                    FTPDataBlock currentBlock = (FTPDataBlock)in.readObject();
                    // create file and write first block to file
                    File file = new File (workingDirectory + File.separator + currentBlock.getFilename());
                    FileOutputStream fOut = new FileOutputStream(file);
                    fOut.write(currentBlock.getData());
                    fOut.flush();
                    // get remaining blocks
                    while(currentBlock.getBlockNumber()+1 <= totalNumBlocks){
                        in = new ObjectInputStream(sock.getInputStream());
                        currentBlock = (FTPDataBlock)in.readObject();
                        fOut.write(currentBlock.getData());
                        fOut.flush();
                    }
                    fOut.close();
                    // send response
                    FTPResponse response = new FTPResponse("File Received OK");
                    out = new ObjectOutputStream(sock.getOutputStream());
                    out.writeObject(response);
                }

ftpdatablock类：

public class FTPDataBlock implements Serializable{
    private static final long serialVersionUID = 1L;
    private String filename;
    private int blockNumber; // current block number
    private byte[] data;
    //constructors & accessors
}

我敢肯定，这是我在这里缺少的很小的东西。有什么想法吗？

Answer 1

这发生了，因为服务器正在编写整个1024个字节块，即使实际写在块上的1024个字节少于1024个字节。

解决方案（感谢@kdgregory）是使用FileInputStream.read()的返回值来填充我的ftpdatablock类中的新属性，int bytesWritten。

然后在服务器端我可以使用：

FileOutputStream.write(currentBlock.getData(), 0, currentBlock.getBytesWritten());

要将确切的字节数写入文件，而不是每次都要整个块。

Answer 2

我认为文件扩展程序可能存在问题。在客户端提供选项：

FILE_TO_RECEIVED = JOptionPane.showInputDialog("Please enter the Drive followed                                  by the file name to be saved. Eg: D:/xyz.jpg");  

它是为了帮助您提供正确的文件扩展名称。

那么我认为您还应该在客户端提供文件大小，例如：

   public final static int FILE_SIZE = 6022386; 

，然后在阵列块中，您可以进行以下更改为：

 try {
  sock = new Socket(SERVER, SOCKET_PORT);
  byte [] mybytearray  = new byte [FILE_SIZE];
  InputStream is = sock.getInputStream();
  fos = new FileOutputStream(FILE_TO_RECEIVED);
  bos = new BufferedOutputStream(fos);
  bytesRead = is.read(mybytearray,0,mybytearray.length);
  current = bytesRead;
  do {
     bytesRead =
        is.read(mybytearray, current, (mybytearray.length-current));
     if(bytesRead >= 0) current += bytesRead;
  } while(bytesRead > -1);
  bos.write(mybytearray, 0 , current);
  bos.flush();

}