如何从 JEditorPane 获取 BufferedImage？

Question

我需要将 URL 加载到 JEditorPane 中，然后从 JEditorPane 中获取 BufferedImge，下面的代码将为我提供 blank/black 图像：

import java.awt.*;
import java.awt.image.*;
import javax.imageio.*;
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.text.html.*;
import java.io.*;

public class Html_Browser
{
  public static void main(String[] args)
  {
    Dimension screenSize=Toolkit.getDefaultToolkit().getScreenSize();
    JEditorPane editorPane=new JEditorPane();
    editorPane.setEditorKit(new HTMLEditorKit());
    editorPane.setEditable(false);

    try
    {
      editorPane.setPage("https://news.yahoo.com/");
      Thread.sleep(3000);
      BufferedImage saveimg=new BufferedImage((int)screenSize.getWidth(),(int)screenSize.getHeight()-36,BufferedImage.TYPE_INT_RGB);
      Graphics2D g2=saveimg.createGraphics();
      editorPane.paint(g2); 
      ImageIO.write(saveimg,"png",new File("test.png"));
    }
    catch (Exception e)
    {
      editorPane.setContentType("text/html");
      editorPane.setText("<html>Connection issues!</html>");
    }
    
    JFrame frame=new JFrame();
    frame.getContentPane().add(editorPane);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setBounds(0,0,(int)screenSize.getWidth(),(int)screenSize.getHeight()-36);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }
}

我添加了 3 秒的延迟，但它不起作用，正确的方法是什么？

Answer 1

您试图在呈现 GUI 之前绘制一个组件，包括该组件，这是行不通的。建议包括：

使用 SwingUtilities.invokeLater()
使用 SwingWorker 在后台线程中加载任何 Web 数据。或者在创建 Swing GUI 之前在主线程中获取网页，然后将其传递给 Swing GUI。
仅在网页已加载且 GUI 已呈现（可见）后创建图像
摆脱所有 Thread.sleep 电话。这些不是你的朋友，只会阻碍 Swing GUI 呈现。

例如：

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.swing.*;

public class EditorStuff extends JPanel {
    private static final String URL_PATH = "https://docs.oracle.com/javase/tutorial/index.html";
    private JEditorPane editorPane;

    public EditorStuff(URL url) throws IOException {
        int w = 800;
        int h = 650;
        setPreferredSize(new Dimension(w, h));
        editorPane = new JEditorPane(url);
        // editorPane.setPage(url);
        JScrollPane scrollPane = new JScrollPane(editorPane);

        setLayout(new BorderLayout());
        add(scrollPane);
    }

    public void captureImage() throws IOException {
        int w = editorPane.getWidth();
        int h = editorPane.getHeight();
        BufferedImage img = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
        Graphics2D g2 = img.createGraphics();
        editorPane.paint(g2);
        ImageIO.write(img, "png", new File("test.png"));
        g2.dispose();
    }

    public static void main(String[] args) {
        try {
            URL url = new URL(URL_PATH);
            SwingUtilities.invokeLater(() -> createAndShowGui(url));
        } catch (IOException ioEx) {
            ioEx.printStackTrace();
        }
    }

    private static void createAndShowGui(final URL url) {
        try {
            EditorStuff mainPanel = new EditorStuff(url);
            JFrame frame = new JFrame("EditorStuff");
            frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
            frame.add(mainPanel);
            frame.pack();
            frame.setLocationByPlatform(true);
            frame.setVisible(true);
            mainPanel.captureImage();  // called *after* rendering
        } catch (IOException ioEx) {
            ioEx.printStackTrace();
        }
    }
}

Answer 2

您或许可以使用这种方法。

修改编辑器面板同步读取所有文件。然后在I/O完成后生成一个PropertyChanngeEvent。

import java.awt.*;
import java.awt.event.*;
import java.beans.*;
import java.io.*;
import java.net.*;
import javax.swing.*;
import javax.swing.text.*;
import javax.swing.text.html.*;
import java.awt.image.*;

public class EditorPaneLoadSynchronously extends JFrame
    implements ActionListener, PropertyChangeListener
{
    private JEditorPane html;
    private JTextField webURL;

    public EditorPaneLoadSynchronously()
    {
        JPanel urlPanel = new JPanel();
        getContentPane().add(urlPanel, BorderLayout.NORTH);

        webURL = new JTextField("https://whosebug.com", 15);
        webURL.addActionListener(this);
        urlPanel.add(webURL);

        JButton gotoURL = new JButton("Goto URL");
        gotoURL.addActionListener(this);
        urlPanel.add(gotoURL);

        HTMLEditorKit editorKit = new HTMLEditorKit()
        {
            private final ViewFactory factory = new HTMLFactory()
            {
                public View create(Element elem)
                {
                    View v = super.create(elem);

                    if ((v != null) && (v instanceof ImageView))
                    {
                        ((ImageView)v).setLoadsSynchronously( true );
                    }

                    return v;
                }
            };

            public ViewFactory getViewFactory()
            {
                return factory;
            }
        };

        html = new JEditorPane();
//      html.setEditorKit( editorKit );
//      html.setEditable( false );
        html.addPropertyChangeListener("page", this);

        JScrollPane scrollPane = new JScrollPane(html);
        scrollPane.setPreferredSize( new Dimension(400, 400) );
        getContentPane().add(scrollPane);
    }

    public void actionPerformed(ActionEvent e)
    {
        try
        {
//          html.setDocument( new HTMLDocument() );
            html.setPage( new URL(webURL.getText()) );
            System.out.println("After setPage");
        }
        catch(Exception exc)
        {
            System.out.println(exc);
        }
    }

    public void propertyChange(PropertyChangeEvent e)
    {
        try
        {
            System.out.println("Page Loaded");
//          BufferedImage bi = ScreenImage.createImage(html);
//          ScreenImage.writeImage(bi, "sync.jpg");
        }
        catch(Exception ee) {}
    }

    private static void createAndShowGUI()
    {
        EditorPaneLoadSynchronously frame = new EditorPaneLoadSynchronously();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationByPlatform( true );
        frame.setVisible( true );

        frame.actionPerformed(null);
    }

    public static void main(String[] args) throws Exception
    {
        java.awt.EventQueue.invokeLater( () -> createAndShowGUI() );
    }
}

注意：以上代码使用了 Screen Image 便利 class。您可以将其替换为您创建和编写 BufferedImage 的唯一代码。

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