DocumentListener is really only good for notification of changes and should never be used to modify a text field/document.
Instead, use a DocumentFilter
Check here for examples
FYI
The root course of your problem is that the DocumentListener is notified WHILE the document is been updated. Attempts to modify the document (apart from risking a infinite loop) put the document into a invalid state, hence the exception
Updated with an example
This is VERY basic example…It doesn’t handle insert or remove, but my testing had remove working without doing anything anyway…
public class TestHighlight {
public static void main(String[] args) {
new TestHighlight();
}
public TestHighlight() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JTextPane textPane = new JTextPane(new DefaultStyledDocument());
((AbstractDocument) textPane.getDocument()).setDocumentFilter(new HighlightDocumentFilter(textPane));
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new JScrollPane(textPane));
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class HighlightDocumentFilter extends DocumentFilter {
private DefaultHighlightPainter highlightPainter = new DefaultHighlightPainter(Color.YELLOW);
private JTextPane textPane;
private SimpleAttributeSet background;
public HighlightDocumentFilter(JTextPane textPane) {
this.textPane = textPane;
background = new SimpleAttributeSet();
StyleConstants.setBackground(background, Color.RED);
}
@Override
public void insertString(FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
System.out.println("insert");
super.insertString(fb, offset, text, attr);
}
@Override
public void remove(FilterBypass fb, int offset, int length) throws BadLocationException {
System.out.println("remove");
super.remove(fb, offset, length);
}
@Override
public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
String match = "test";
super.replace(fb, offset, length, text, attrs);
int startIndex = offset - match.length();
if (startIndex >= 0) {
String last = fb.getDocument().getText(startIndex, match.length()).trim();
System.out.println(last);
if (last.equalsIgnoreCase(match)) {
textPane.getHighlighter().addHighlight(startIndex, startIndex + match.length(), highlightPainter);
}
}
}
}
}