try {
    // Get the text pane's document
    JTextPane textPane = new JTextPane();
    StyledDocument doc = (StyledDocument)textPane.getDocument();

    // The component must first be wrapped in a style
    Style style = doc.addStyle("StyleName", null);
    StyleConstants.setComponent(style, new JButton("OK"));

    // Insert the component at the end of the text
    doc.insertString(doc.getLength(), "ignored text", style);
} catch (BadLocationException e) {
}