Java JFrame画图

Question

我以前遇到过这个问题，但我不记得我是如何解决的。我正在研究 RAT，到目前为止它只是将客户端屏幕发送到服务器。我曾经将图像保存到磁盘，但现在我试图让它只显示在 JFrame 上。它显示第一个屏幕截图，但仅显示第一个屏幕截图，不会绘制新屏幕截图。

服务器:

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.net.ServerSocket;
import java.net.Socket;

import javax.imageio.ImageIO;
import javax.swing.JFrame;

@SuppressWarnings("serial")
public class Server extends JFrame {

private BufferedImage image;
private BufferedImage oldImage;

public Server() {
    setTitle("RAT");
    setResizable(false);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

public static void main(String[] args) throws IOException {
    try {
        Server server = new Server();

        ServerSocket serverSocket = new ServerSocket(25565);
        Socket clientSocket = serverSocket.accept();
        System.out.println("Connection accepted!");

        ObjectInputStream in = new ObjectInputStream(clientSocket.getInputStream());
        boolean firstConnection = true;

        int width = 0;
        int height = 0;

        while (true) {
            if(firstConnection) {
                width = in.readShort();
                height = in.readShort();
                server.setSize(width, height);
                server.setVisible(true);
                firstConnection = false;
            }
            server.oldImage = ImageIO.read(in);
            if(server.oldImage != null) {
                server.image = server.oldImage;
            }
            server.repaint();

        }
    } catch (IOException e) {
        System.err.println("Accept failed.");
        System.exit(1);
    }
}

public void paint(Graphics g) {
    g.drawImage(image, 0, 0, this);
}
}

客户:

import java.awt.AWTException;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.net.Socket;

import javax.imageio.ImageIO;

public class Client {

public static void main(String[] args) {
    try {
        Socket socket = new Socket("127.0.0.1", 25565);
        ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
        Robot robot = new Robot();
        Toolkit toolkit = Toolkit.getDefaultToolkit();
        Rectangle rectangle = new Rectangle(toolkit.getScreenSize());
        out.writeShort(toolkit.getScreenSize().width);
        out.writeShort(toolkit.getScreenSize().height);

        while(true) {
            ImageIO.write(robot.createScreenCapture(rectangle), "jpg", out);
            Thread.sleep(200);
        }
    } catch (AWTException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}
}

Answer 1

据我所知，问题是你通过编写诸如 Thread.sleep() 或 while(true) 之类的东西来阻止事件调度线程，从 Swing 的角度来看，这实际上并不称为适合。

你可以做些什么来解决这个问题:

• 将循环结构放入内部SwingWorker .
• 直接使用Socket之类的代码片段 clientSocket =
serverSocket.accept(); 阻止 EDT，因此这些东西必须是在单独的 Thread 或在 SwingWorker 中完成。
• 对 repaint() 的递归调用合并了来自 Filthy 的引述Rich Clients 就上述主题的论证如下

---

It is important to note that repaint requests get “coalesced,” or combined. 
So, for example, if you request a repaint and there is already one on the 
queue that has not yet been serviced, then the second request is ignored 
because your request for a repaint will already be fulfilled by the earlier 
request. This behavior is particularly helpful in situations where many
repaint requests are being generated, perhaps by very different situations 
and components, and Swing should avoid processing redundant requests and 
wasting effort.

---

• 不是直接在您的 JFrame 上绘画，而是明智的做法是通过重写在 JPanel/JComponent 之上绘制它 paintComponent(...)方法。
• 递归 Paint 调用可以通过使用 paintImmediately(Rectangle rect)或 paintImmediately(int x, inty, int w, int h) , 方法。

这里是一个示例程序以获得进一步的帮助:

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class PointsExample
{   
    private CustomPanel contentPane;
    private Timer timer;
    private int x = 1;
    private int y = 1;

    /*
     * This is just JFrame, that we be 
     * using as the Base for our Application.
     * Though here we are calling our
     * JPanel (CustomPanel), whose
     * paintComponent(...) method, we had
     * override.
     */
    private void createAndDisplayGUI()
    {
        JFrame frame = new JFrame("Locate Mouse Position");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        contentPane = new CustomPanel();
        frame.setContentPane(contentPane);  
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);

        for (int i = 0; i < 500; i++)
        {
            contentPane.set(x, y);
            x++;
            y++;
            if (x == 450)
                break;
        }
    }

    public static void main(String\u005B\u005D args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new PointsExample().createAndDisplayGUI();
            }
        });
    }
}

class CustomPanel extends JComponent
{
    private int x;
    private int y;

    public void set(int a, int b)
    {
        x = a;
        y = b;
        paintImmediately(0, 0, getWidth(), getHeight());

    }   

    @Override
    public Dimension getPreferredSize()
    {
        return (new Dimension(500, 500));
    }

    @Override
    public void paintComponent(Graphics g)
    { 
        super.paintComponent(g);
        g.clearRect(0, 0, getWidth(), getHeight());
        g.fillOval(x, y, 4, 4);                        
    }
}