Java 为什么textPane.getDocument（）.getText（）返回空字符串？

如果试图从内容类型为“text/html”的JTextPane组件中获取文本（换行符在其位置上），我在这里做错了什么

textPane.getText（）

返回HTML，但头和体为空。

textPane.getDocument（）.getText（）

返回空字符串

注：在同一代码中，我也没有换行和其他问题，我应该用相同的代码作为独立问题来问它们吗

代码：

package test;

import java.io.IOException;
import java.io.StringReader;
import java.net.URL;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JScrollPane;
import javax.swing.text.BadLocationException;
//import javax.swing.text.StyledEditorKit;

public class TextPaneTester extends javax.swing.JFrame {

    public TextPaneTester() {
        initComponents();
        myInitComponents();
    }

    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {
        contentScrollPane = new javax.swing.JScrollPane();
        content = new javax.swing.JTextPane();
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        contentScrollPane.setViewportView(content);

        // layout code by NetBeans
    }// </editor-fold>                        

    private void myInitComponents(){
        //content.setEditorKit(new StyledEditorKit());
        contentScrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        contentScrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
    }

    private void fetchURL(String url){
        try{
            // URL(URL baseURL[, String relativeURL])
            URL helpURL = new URL(url);
            System.out.println(helpURL);
            this.content.setPage(helpURL);

            try {
                System.out.println("This far!");
                //System.out.println(this.content.getDocument());
                System.out.println("getDocument() on JTextPane gives " + this.content.getDocument());
                System.out.println("getText() on JTextPane gives " + this.content.getText());

                // Why this line retuens an empty string?
                String text = this.content.getDocument().getText(0, this.content.getDocument().getLength());
                System.out.println("getDocument.getText() on JTextPane gives " + text);

                System.out.println("This far 2!");
                // this.translation.setPage(helpURL);
            } catch (BadLocationException ex) {
                System.out.println("Why this far!");
                Logger.getLogger(TextPaneTester.class.getName()).log(Level.SEVERE, null, ex);
            }

        }
        catch (IOException e) {
            System.err.println("Attempted to read a bad URL: " + url);
        }
        // return this.content;
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(TextPaneTester.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(TextPaneTester.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(TextPaneTester.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(TextPaneTester.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                String url = "https://en.wikipedia.org/wiki/Virtaal";
                TextPaneTester reader = new TextPaneTester();
                reader.fetchURL(url);
                reader.setVisible(true);
            }
        });
    }

    private javax.swing.JTextPane content;
    private javax.swing.JScrollPane contentScrollPane;
    // End of variables declaration                   
}

run:
https://en.wikipedia.org/wiki/Virtaal
This far!
getDocument() on JTextPane gives javax.swing.text.html.HTMLDocument@1767743f
getText() on JTextPane gives <html>
  <head>

  </head>
  <body>
    <p style="margin-top: 0">

    </p>
  </body>
</html>

getDocument.getText() on JTextPane gives 
This far 2!
<html>
  <head>

  </head>
  <body>
    <p style="margin-top: 0">

    </p>
  </body>
</html>

Let's see what the parser gives: 
BUILD SUCCESSFUL (total time: 55 seconds)

封装测试；
导入java.io.IOException；
导入java.io.StringReader；
导入java.net.URL；
导入java.util.logging.Level；
导入java.util.logging.Logger；
导入javax.swing.JScrollPane；
导入javax.swing.text.BadLocationException；
//导入javax.swing.text.StyledEditorKit；
公共类TextPaneTester扩展了javax.swing.JFrame{
public TextPaneTester（）{
初始化组件（）；
myInitComponents（）；
}
//                           
私有组件（）{
contentScrollPane=newjavax.swing.JScrollPane（）；
content=newjavax.swing.JTextPane（）；
setDefaultCloseOperation（javax.swing.WindowConstants.EXIT_ON_CLOSE）；
contentScrollPane.setViewportView（内容）；
//NetBeans的布局代码
}//                         
私有void myInitComponents（）{
//setEditorKit（新的StyledEditorKit（））；
contentScrollPane.setVerticalScrollBarPolicy（JScrollPane.VERTICAL\u SCROLLBAR\u ALWAYS）；
contentScrollPane.setHorizontalScrollBarPolicy（JScrollPane.HorizontalScrollBar\uNever）；
}
私有void fetchURL（字符串url）{
试一试{
//URL（URL baseURL[，字符串相对值]）
URL helpURL=新URL（URL）；
System.out.println（helpURL）；
this.content.setPage（helpURL）；
试一试{
System.out.println（“到此为止！”）；
//System.out.println（this.content.getDocument（））；
System.out.println（“JTextPane上的getDocument（）给出”+this.content.getDocument（））；
System.out.println（“JTextPane上的getText（）给出“+this.content.getText（））；
//为什么这行复述空字符串？
String text=this.content.getDocument（）.getText（0，this.content.getDocument（）.getLength（））；
System.out.println（“JTextPane上的getDocument.getText（）给出“+text”）；
System.out.println（“ThisFar2！”）；
//this.translation.setPage（helpURL）；
}捕获（BadLocationException ex）{
System.out.println（“为什么这么远！”）；
Logger.getLogger（TextPaneTester.class.getName（））.log（Level.SEVERE，null，ex）；
}
}
捕获（IOE异常）{
System.err.println（“试图读取错误的URL:+URL”）；
}
//返回此.content；
}
/**
*@param指定命令行参数
*/
公共静态void main（字符串参数[]）{
/*设置Nimbus的外观和感觉*/
//
/*如果Nimbus（在JavaSE6中引入）不可用，请使用默认的外观。
*详情请参阅http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
*/
试一试{
for（javax.swing.UIManager.LookAndFeelInfo:javax.swing.UIManager.getInstalledLookAndFeels（））{
if（“Nimbus”.equals（info.getName（）））{
setLookAndFeel（info.getClassName（））；
打破
}
}
}捕获（ClassNotFoundException ex）{
getLogger（TextPaneTester.class.getName（））.log（java.util.logging.Level.SEVERE，null，ex）；
}catch（实例化异常）{
getLogger（TextPaneTester.class.getName（））.log（java.util.logging.Level.SEVERE，null，ex）；
}捕获（非法访问例外）{
getLogger（TextPaneTester.class.getName（））.log（java.util.logging.Level.SEVERE，null，ex）；
}catch（javax.swing.UnsupportedLookAndFeelException ex）{
getLogger（TextPaneTester.class.getName（））.log（java.util.logging.Level.SEVERE，null，ex）；
}
//
/*创建并显示表单*/
invokeLater（new Runnable（））{
@凌驾
公开募捐{
字符串url=”https://en.wikipedia.org/wiki/Virtaal";
TextPaneTester reader=newtextpanetester（）；
reader.fetchURL（url）；
reader.setVisible（true）；
}
});
}
私有javax.swing.JTextPane内容；
私有javax.swing.JScrollPane内容滚动窗格；
//变量结束声明
}

输出：

package test;

import java.io.IOException;
import java.io.StringReader;
import java.net.URL;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JScrollPane;
import javax.swing.text.BadLocationException;
//import javax.swing.text.StyledEditorKit;

public class TextPaneTester extends javax.swing.JFrame {

    public TextPaneTester() {
        initComponents();
        myInitComponents();
    }

    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {
        contentScrollPane = new javax.swing.JScrollPane();
        content = new javax.swing.JTextPane();
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        contentScrollPane.setViewportView(content);

        // layout code by NetBeans
    }// </editor-fold>                        

    private void myInitComponents(){
        //content.setEditorKit(new StyledEditorKit());
        contentScrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        contentScrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
    }

    private void fetchURL(String url){
        try{
            // URL(URL baseURL[, String relativeURL])
            URL helpURL = new URL(url);
            System.out.println(helpURL);
            this.content.setPage(helpURL);

            try {
                System.out.println("This far!");
                //System.out.println(this.content.getDocument());
                System.out.println("getDocument() on JTextPane gives " + this.content.getDocument());
                System.out.println("getText() on JTextPane gives " + this.content.getText());

                // Why this line retuens an empty string?
                String text = this.content.getDocument().getText(0, this.content.getDocument().getLength());
                System.out.println("getDocument.getText() on JTextPane gives " + text);

                System.out.println("This far 2!");
                // this.translation.setPage(helpURL);
            } catch (BadLocationException ex) {
                System.out.println("Why this far!");
                Logger.getLogger(TextPaneTester.class.getName()).log(Level.SEVERE, null, ex);
            }

        }
        catch (IOException e) {
            System.err.println("Attempted to read a bad URL: " + url);
        }
        // return this.content;
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(TextPaneTester.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(TextPaneTester.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(TextPaneTester.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(TextPaneTester.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                String url = "https://en.wikipedia.org/wiki/Virtaal";
                TextPaneTester reader = new TextPaneTester();
                reader.fetchURL(url);
                reader.setVisible(true);
            }
        });
    }

    private javax.swing.JTextPane content;
    private javax.swing.JScrollPane contentScrollPane;
    // End of variables declaration                   
}

run:
https://en.wikipedia.org/wiki/Virtaal
This far!
getDocument() on JTextPane gives javax.swing.text.html.HTMLDocument@1767743f
getText() on JTextPane gives <html>
  <head>

  </head>
  <body>
    <p style="margin-top: 0">

    </p>
  </body>
</html>

getDocument.getText() on JTextPane gives 
This far 2!
<html>
  <head>

  </head>
  <body>
    <p style="margin-top: 0">

    </p>
  </body>
</html>

Let's see what the parser gives: 
BUILD SUCCESSFUL (total time: 55 seconds)

运行：
https://en.wikipedia.org/wiki/Virtaal
这么远！
JTextPane上的getDocument（）提供javax.swing.text.html。HTMLDocument@1767743f
JTextPane上的getText（）提供


JTextPane上的getDocument.getText（）提供
这么远！


让我们看看解析器给出了什么：
构建成功（总时间：55秒）

与往常一样，您应该首先查看：

如果以异步方式加载文档，则将使用调用

setDocument

立即将文档安装到编辑器中，该调用将触发文档属性更改事件，然后将创建一个线程，该线程将开始实际加载。在这种情况下，调用此方法不会直接触发页面属性更改事件，而是在执行加载的线程完成后触发。它还将在事件分派线程上激发。