我正在尝试通过套接字发送一个文件，当前从客户端发送到服务器。要写入的文件已创建，但当我打开它时，它是空的。另外，如果我在发送文件之后向服务器发送一个字符串，那么我发送的内容会被写入应该接收的文本文件中。
我只测试文本文件。
为什么会这样？我怎样才能纠正它？

jbutton.addActionListener(
                new ActionListener() {
                    public void actionPerformed(ActionEvent event) {
                        JFileChooser fc = new JFileChooser();
                        fc.setCurrentDirectory(new File(System.getProperty("user.home")));
                        FileNameExtensionFilter filter = new FileNameExtensionFilter("*.Images", "jpg","gif","png","txt");
                        fc.addChoosableFileFilter(filter);
                        int result = fc.showSaveDialog(null);
                         if(result == JFileChooser.APPROVE_OPTION){
                             File selectedFile = fc.getSelectedFile();
                             String path = selectedFile.getAbsolutePath();
                            try {
                                userText.setText("Sending File: " + selectedFile);
                                file = new FileInputStream(path);
                                byte b[] = new byte[30000];
                                file.read(b,0,b.length);
                                os = connection.getOutputStream();
                                os.write(b,0,b.length);

                            } catch (FileNotFoundException e) {
                                e.printStackTrace();
                            }
                            catch (IOException e) {
                                e.printStackTrace();
                            }

                         }
                         else if(result == JFileChooser.CANCEL_OPTION){
                             System.out.println("No File Select");
                         }  
                    }

//get stream to send and receive data 
    private void setupStreams() throws IOException{
        output = new ObjectOutputStream(socket.getOutputStream());
        output.flush();
        input = new ObjectInputStream(socket.getInputStream());
        showMessage("\n Streams Are now Set up \n");
    }

    //during the chat conversation
    private void whileChatting() throws IOException{
        String message = "You are now connected ";
        showMessage(message);
        ableToType(true);
        do {
            try {
                message = (String) input.readObject();
                showMessage("\n" + message);

                byte b[] = new byte[30000];
                InputStream is = socket.getInputStream();
                FileOutputStream fr = new FileOutputStream("C:\\Users\\Documents\\TestingFileClientToServer.txt");
                is.read(b,0,b.length);
                fr.write(b,0,b.length);

            }catch(ClassNotFoundException classNotFoundException) {
                showMessage("\n Error on input \n");
            }

        }while(!message.equals("CLIENT - END"));
    }