java - 在java中客户端获取负字节数组长度或大量字节数组长度

Question

我正在将图像从服务器传输到客户端。服务器捕获屏幕并将其转换为字节数组，客户端接收字节数组并将其转换回图像。但只传输了几帧，然后就发生了错误。

接收方:

while(true) {
    DataInputStream dis = new DataInputStream(csocket.getInputStream());
    int len = dis.readInt();
    System.out.println(len);
    byte data[] = null;
    data = new byte[len];
    dis.read(data);
    ByteArrayInputStream in = new ByteArrayInputStream(data);
    BufferedImage image1=ImageIO.read(in);
    ImageIcon imageIcon= new ImageIcon(image1);
    Image image = imageIcon.getImage();
    image = image.getScaledInstance(cPanel.getWidth(),cPanel.getHeight(),Image.SCALE_FAST);
    //Draw the recieved screenshot
    Graphics graphics = cPanel.getGraphics();
    graphics.drawImage(image, 0, 0, cPanel.getWidth(),cPanel.getHeight(),cPanel);
}

发送方:

while(continueLoop) {
    try {
        BufferedImage image = robot.createScreenCapture(rectangle);
        byte[] imageInByte;
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write(image,"jpg", baos);
        baos.flush();
        imageInByte = baos.toByteArray();
        baos.close();
        DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
        //PrintWriter out = new PrintWriter(socket.getOutputStream());

        //out.flush();
        dos.writeInt(imageInByte.length);
        System.out.println(imageInByte.length);
        dos.write(imageInByte);
        Thread.sleep(1000);
        dos.flush();
    }
    catch(Exception e) {
    }
}

接收器的输出:

 1177222283
 -297418067
 1228900861
 -412483840
 189486847
 10536391
 -33405441
 12898815
 740182
 -16736067
 -805436987 
 -16726825
 258150991
 2137853087
 1917408603
 512024791 
 -1227886373
 -1034512766
 1772271848
 157387
 Exception in thread "Thread-3" java.lang.NullPointerException
 at javax.swing.ImageIcon.<init>(ImageIcon.java:228)
 at remoteclient.ClientScreenReciever.run(ClientScreenReciever.java:65)                                                                                                                                            

请帮助我......如何在java中以更快的方式通过套接字将图像从服务器连续传输到客户端。

Answer 1

您正在使用

DataInputStream#read(byte[])

其中(检查其 Javadoc)不保证将读取完整数组的数据。此方法用于缓冲读取，而不是完全读取请求的字节数。

相反，您必须调用

DataInputStream#readFully(byte[])

其中有适合您目的的契约(Contract)(再次检查 Javadoc)。