java - 如何通过java中的套接字发送图像？

Question

我正在编写一个客户端-服务器程序，我希望它能发送图像。 代码如下:

//RECEIVER
while(true){
  try{
            socket = server.accept();

            out = new ObjectOutputStream(socket.getOutputStream());
            out.flush();
            in = new ObjectInputStream(socket.getInputStream());

            System.out.println("Connected to "+PORTA+".");

            while(!socket.isClosed()){ 
                System.out.println("\nPrint the action");
                azione = reader.readLine();

           if(azione.equals("screenshot")){

                    out.writeObject("screenshot");
                    out.flush();
                    BufferedImage screenshot = ImageIO.read(in);

                    ImageIO.write(screenshot, "jpg", new File("screenshot.jpg"));
                }
  }catch(Exception ex){
            System.out.println("Not connected.\n");
  } 
}

和服务器:

while(true){ 
   try{
            socket = new Socket(INDIRIZZO, PORT);

            out = new ObjectOutputStream(socket.getOutputStream());
            out.flush();
            in = new ObjectInputStream(socket.getInputStream());

            while(!socket.isClosed()){
                try {
                  action = (String)in.readObject();
                  if(azione.equals("screenshot")){
                        BufferedImage screenshot = new Robot().createScreenCapture(new Rectangle(Toolkit.getDefaultToolkit().getScreenSize()));
                        ImageIO.write(screenshot, "jpg", out);
                    }catch(Exception e){

                    }
            }
   }catch(Exception ex){
      //
   }
}

我的问题是客户端只有在我关闭套接字或输出流时才会收到图像，但我不希望这种情况发生。 我怎样才能绕过它？如何以字节形式发送图像？谢谢!

Answer 1

问题是 ImageIO.read 等待流结束。套接字仅在您关闭它时发送它。 (这是有道理的)

您要做的是首先发送图像的大小，然后在接收端以字节数组形式读取图像。

public class Send {

    public static void main(String[] args) throws Exception {
        Socket socket = new Socket("localhost", 13085);
        OutputStream outputStream = socket.getOutputStream();

        BufferedImage image = ImageIO.read(new File("C:\\Users\\Jakub\\Pictures\\test.jpg"));

        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        ImageIO.write(image, "jpg", byteArrayOutputStream);

        byte[] size = ByteBuffer.allocate(4).putInt(byteArrayOutputStream.size()).array();
        outputStream.write(size);
        outputStream.write(byteArrayOutputStream.toByteArray());
        outputStream.flush();
        System.out.println("Flushed: " + System.currentTimeMillis());

        Thread.sleep(120000);
        System.out.println("Closing: " + System.currentTimeMillis());
        socket.close();
    }
}


public class Receive {

    public static void main(String[] args) throws Exception {
        ServerSocket serverSocket = new ServerSocket(13085);
        Socket socket = serverSocket.accept();
        InputStream inputStream = socket.getInputStream();

        System.out.println("Reading: " + System.currentTimeMillis());

        byte[] sizeAr = new byte[4];
        inputStream.read(sizeAr);
        int size = ByteBuffer.wrap(sizeAr).asIntBuffer().get();

        byte[] imageAr = new byte[size];
        inputStream.read(imageAr);

        BufferedImage image = ImageIO.read(new ByteArrayInputStream(imageAr));

        System.out.println("Received " + image.getHeight() + "x" + image.getWidth() + ": " + System.currentTimeMillis());
        ImageIO.write(image, "jpg", new File("C:\\Users\\Jakub\\Pictures\\test2.jpg"));

        serverSocket.close();
    }

}