如何確定JFrame的繪圖狀態？

您可以使用SwingUtilities調用器。根據文檔，invokeLater導致在AWT事件調度thread上異步執行doRun.run(。這將在處理完所有掛起的AWT事件后發生。因此，將在框架/面板繪圖完成后捕獲屏幕截圖。

Update

正如@camickr正確指出的，確保您的GUI也是以類似的方式創建的，即在AWT事件調度Thread（EDT）上。下面的例子。

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class ScreenCapture {
    JFrame jFrame = null;

    public void createGUI() {
        JPanel jPanel = new JPanel();
        for (int i = 1; i < 1000; i++) {
            jPanel.add(new JLabel(String.valueOf(i)));
        }

        jFrame = new JFrame();
        jFrame.setSize(500, 500);
        jFrame.setContentPane(jPanel);
        jFrame.setVisible(true);
    }

    public void capture() {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                try {
                    BufferedImage img = captureFrame(jFrame);
                    ImageIO.write(img, "png", new File("tmp/1.png"));
                } catch (AWTException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public static void main(String[] args) {
        ScreenCapture sc = new ScreenCapture();
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                sc.createGUI();
                sc.capture();
            }
        });
    }

    public static BufferedImage captureFrame(JFrame window) throws AWTException {
        Robot robot = new Robot();
        window.setAlwaysOnTop(true);
        Point windowPoint = window.getLocation();
        Dimension windowSize = window.getSize();
        Rectangle rectangle = new Rectangle((int) windowPoint.getX(), (int) windowPoint.getY(), windowSize.width,
                windowSize.height);
        return robot.createScreenCapture(rectangle);
    }
}