Double List Item insertion in JTextPane

I have a button that inserts an unordered list item into a JTextPane. However, when I click on the button to insert a list item, two bullets are inserted instead of one. One bullet is inserted only during the first time insertion.

I cut out the functionality from my application and pasted the code into a small SSCCE (below) and the problem remains. Does anyone have any idea as to what might be happening here?

[The problem has been solved, below is the complete solved code. There are two ways to do this, refer to the functionality in the show and the bullets button]

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.HeadlessException;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;

import javax.swing.JButton;
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextPane;
import javax.swing.text.BadLocationException;
import javax.swing.text.Element;
import javax.swing.text.ElementIterator;
import javax.swing.text.html.HTML;
import javax.swing.text.html.HTMLDocument;
import javax.swing.text.html.HTMLEditorKit;

public class Main {

    private static Button2 show = new Button2 ("Show"); 
    private static LIButton bullets = new LIButton("Bullets", HTML.Tag.UL);
    private static JEditorPane pane = new JEditorPane();

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                create();
            }
        });
    }

    private static void create() throws HeadlessException {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pane.setPreferredSize(new Dimension(300, 300));
        pane.setContentType("text/html");
        frame.add(pane, BorderLayout.CENTER);
        JPanel panel = new JPanel();
        panel.add(bullets);
        panel.add(show);
        frame.add(panel, BorderLayout.SOUTH);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    static class LIButton extends JButton {

        static final String LI_HTML = "<HTML><BODY><UL><LI></LI></UL></BODY></HTML>";

        public LIButton(String name, HTML.Tag parent) {
            super(new HTMLEditorKit.InsertHTMLTextAction(
                name, LI_HTML, HTML.Tag.UL, HTML.Tag.LI, HTML.Tag.BODY, HTML.Tag.UL));
        }
    }

    static class Button2 extends JButton implements ActionListener {

        static final String LI_HTML = "<HTML><BODY><UL><LI></LI></UL></BODY></HTML>";

        public Button2(String name) {
            super(name);
            this.addActionListener(this);
        }

        @Override
        public void actionPerformed(ActionEvent ae) {
            HTMLDocument doc = (HTMLDocument) pane.getDocument();
            HTMLEditorKit kit = (HTMLEditorKit) pane.getEditorKit();

            try {
                kit.insertHTML(doc, doc.getLength() - 1, LI_HTML, 0, 1, null);
            } catch (BadLocationException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

}

Solution

The example below seems to work.

enter image description here

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.HeadlessException;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextPane;
import javax.swing.text.html.HTML;
import javax.swing.text.html.HTMLEditorKit;

public class Main {

    private static LIButton bullets = new LIButton("Bullets", HTML.Tag.UL);
    private static JTextPane pane = new JTextPane();

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                create();
            }
        });
    }

    private static void create() throws HeadlessException {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pane.setPreferredSize(new Dimension(300, 300));
        pane.setContentType("text/html");
        pane.setText("<HTML><BODY><UL></UL></BODY></HTML>");
        frame.add(pane, BorderLayout.CENTER);
        JPanel panel = new JPanel();
        panel.add(bullets);
        frame.add(panel, BorderLayout.SOUTH);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    static class LIButton extends JButton {

        static final String LI_HTML = "<LI>item</LI>";

        public LIButton(String name, HTML.Tag parent) {
            super(new HTMLEditorKit.InsertHTMLTextAction(
                name, LI_HTML, parent, HTML.Tag.LI));
        }
    }
}