Java - FTP 程序在传输过程中损坏文件

Question

我已经使用套接字制作了一个基本的客户端服务器 FTP 程序，但由于某种原因文件在传输过程中被损坏。在下面的例子中，我将文件从客户端推送到服务器。它几乎可以工作，因为某些文件(例如 .png)可以正常传输和打开，但其他文件(.docx)则不能。我传输的任何文件都具有与我发送的文件不同的 MD5。

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
}

我确信我在这里遗漏了一些小东西。有什么想法吗？

Answer 1

发生这种情况是因为服务器正在将整个 1024 字节 block 写入文件，即使实际写入该 block 的字节数少于 1024 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());

将确切的字节数写入文件，而不是每次都写入整个 block 。