java - 套接字，发送的 pdf 文件始终到达零字节大小

Question

我正在从 Android 平板电脑客户端向在 Windows 7 上运行的 Java 应用程序发送一个 pdf 文件。该文件始终以零字节大小到达。这里有什么问题？

在pdf文件从客户端发送到服务器之前，文件的大小作为long值从客户端发送到服务器，这个大小是正确的并且总是到达服务器。对于 pdf 文件，我用于此测试的大小为 566718 字节。

如何获得正确大小的 pdf 文件？

服务器代码

 public class Server {
 ServerSocket serverSocket;
 Socket socket;
 boolean runner = true;

Server() throws IOException{

    serverRunner();
    System.out.println("server constructor started");

} // Server() constructor

public void serverRunner() throws IOException {

    System.out.println("serverrunner started");

     try {

      serverSocket = new ServerSocket(6789, 100);

      runner = true;

        while (runner) {

            socket = serverSocket.accept();

            MultiThreader multi = new MultiThreader(socket);
            Thread t = new Thread(multi);
            t.start();

        }  // while runner
       } catch (IOException ex) {

    }

 } // serverRunner()

 } // class Server


public class MultiThreader implements Runnable {
Socket socket;
public int fileSizeFromClient;
FileOutputStream fos = null;
BufferedInputStream bis = null;
BufferedOutputStream bos = null;
DataInputStream dis = null;
DataOutputStream dos = null;

public MultiThreader(Socket socket){
    System.out.println("print out from multithreader class");
    this.socket = socket;

} // multiThreader

@Override
public void run() {

    System.out.println("multi threader started");

    // action #1 read file from client =====================================
    // transfer.pdf read this file sent from android device to this computer

    int bufferSize = 0;

    try {

     bis = new BufferedInputStream(socket.getInputStream());
     dis = new DataInputStream(bis);

     fileSizeFromClient = dis.readInt();
     System.out.println("file size from client is " + fileSizeFromClient);

      File fileDirectory = new File("C:/DOWNLOAD/");
        if (!fileDirectory.exists()) {
            fileDirectory.mkdir();
      }
      File file = new File("C:/DOWNLOAD/transfer.pdf");
      file.createNewFile();

       fos = new FileOutputStream(file);
       bos = new BufferedOutputStream(fos);
       dos = new DataOutputStream(bos);

       byte[] buffer = new byte[fileSizeFromClient];

      int totalBytesRead = 0;

        while(totalBytesRead < fileSizeFromClient){
            int bytesRemaining = fileSizeFromClient = totalBytesRead;
            int bytesRead = dis.read(buffer, 0, (int) Math.min(buffer.length, bytesRemaining));
            if(bytesRead == -1) {
                break;
            } else {
                dos.write(buffer, 0, bytesRead); 
                    totalBytesRead += bytesRead;
            }
        } // while

      } catch (IOException ex) {
        Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE, null, ex);
      } finally {
        try {
          //  socket.close();
        } catch (IOException ex) {
            Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

} // run

} // MultiThreader

客户端代码

 public class MainActivity extends Activity implements Runnable {

TextView textViewOne;
Button buttonOne;
Socket socket;
private String serverIP = "192.XXX.X.X";
FileInputStream fis;
FileOutputStream fos;
private File file;
DataInputStream dis;
DataOutputStream dos;
BufferedInputStream bis;
BufferedOutputStream bos;
long length;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

   textViewOne = (TextView) findViewById(R.id.textView1);
   buttonOne = (Button) findViewById(R.id.button1);

   buttonOne.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View v) {
        Thread myThread = new Thread(MainActivity.this);
        myThread.start();

    }

   });

} // oncreate

@Override
public void run() {

    MainActivity.this.runOnUiThread(new Runnable(){
        @Override
        public void run() {
           textViewOne.setText("run method started");
        }
        });

    try {
        socket = new Socket(InetAddress.getByName(serverIP), 6789);

        if (socket == null) {
            return;
        } else {
            MainActivity.this.runOnUiThread(new Runnable(){
                @Override
                public void run() {
                   textViewOne.setText("connected");
                }
                });

        }

        file = new File(Environment.getExternalStorageDirectory().getPath() + File.separator + "transfer.pdf");

        length = file.length();

        fis = new FileInputStream(file);
        bis = new BufferedInputStream(fis);
        dis = new DataInputStream(bis);

        bos = new BufferedOutputStream(socket.getOutputStream());
        dos = new DataOutputStream(bos);

        dos.writeInt((int) length); // sends the length as number bytes is file size

        int count = 0;
        byte[] buffer = new byte[(int) length];

        while ((count = bis.read(buffer)) > 0)
        {
            bos.write(buffer, 0, count);
        }

        bos.flush();
        bis.close();
        socket.close();

    } catch (UnknownHostException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

 } // mainactivity

Answer 1

我相信这就是问题所在。

int bytesRemaining = fileSizeFromClient = totalBytesRead;

这会进行两次赋值，因此您要立即将 0 赋值给 fileSizeFromClient，然后退出循环。

你的意思是:

int bytesRemaining = fileSizeFromClient - totalBytesRead;

这是一个非常微妙的拼写错误，你很不幸，它仍然导致了有效的代码:(

鉴于您无论如何都会立即关闭套接字，目前尚不清楚为什么您要首先发送文件大小。如果您在客户端和服务器上都具有相同的“从输入流复制到输出流，直到输入用完数据”，只需从 FileInputStream 到客户端的 Socket 的 OutputStream，以及 Socket 的 InputStream 到 FileOutputStream(可能带有缓冲包装器)在服务器上。

我还建议关闭所有流 - 如果您使用的是 Java 7，则只需使用 try-with-resources 语句即可完成此操作；在早期版本中，您应该在 finally block 中关闭流。