java.lang.IllegalStateException while using Document Listener in TextArea, Java

Question

DocumentListener dl = new MessageDocumentListener();
((AbstractDocument) nboxArea.getDocument()).setDocumentFilter(new DocumentFilter() {
    public void insertString(FilterBypass fb, int offset, String string, AttributeSet attr) throws BadLocationException {
        string = string.replaceAll("\t", "");
        super.insertString(fb, offset, string,(javax.swing.text.AttributeSet) attr);
    }

    public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
        text = text.replaceAll("\t", "");
        //TODO must do something here
        super.replace(fb, offset, length, text,(javax.swing.text.AttributeSet) attrs);
    }
});

JTextArea evArea = (JTextArea) c;
evArea.getDocument().removeDocumentListener(dl);
evArea.setText(originalMessage);

In this case I found the following error during set text in textarea. I do not know how to resolve.

Exception in thread "AWT-EventQueue-0" 
java.lang.IllegalStateException: Attempt to mutate in notification

I think the problem is to set text in document or setting document in document listener. But I do not know how to solve this. Please help me to solve this issue.

Answer 1

You cannot modify the document inside the DocumentListener. Write a custom Document instead, which overrides the insertString() or remove() methods.

From Java Tutorials: How to write a DocumentListener

Document listeners should not modify the contents of the document; The change is already complete by the time the listener is notified of the change. Instead, write a custom document that overrides the insertString or remove methods, or both. See Listening for Changes on a Document for details.

Answer 2

If you want to mutate in the listener you can launch a separate thread to do it later with SwingUtilities.invokeLater. Be careful because the modifications from the separate thread will call the listener again, so set a boolean before launching the thread, return immediately from the listener if it is set and reset it after the modifications have been done in the separate thread.