How to insert a String at the CaretPosition without moving the Caret?

Question

I have a JTextPane wrapped by a JScrollPane. The JTextPane is where chatroom messages appear. When a message is appended at the end, it determines whether to scroll to the bottom based on some conditions (scroll to the bottom only if the user was already viewing somewhere near the bottom). That part is working fine.
Although the JTextPane is not editable, it allows the user to make selections using a mouse so that blocks of text can be copied from the chatroom. The default caret of JTextPane handles that for me.
But the problem comes when the caret position is at the end of the document when my program inserts a new message with the following code:
StyledDocument doc = textPane.getStyledDocument();
doc.insertString(doc.getLength(), message + "\n", null);The caret was at doc.getLength() to begin with, when the new message is inserted at the end, it "pushes" the caret to a new position. The caret movement is causing JScrollPane to scroll to where the caret is visible (the bottom), therefore interfering with my scrolling algorithm (see above).
So, when the caret is doc.getLength(), how do I insert a String at doc.getLength() with the caret staying at the original position?
In other words, how do I insert a String at the caret position without the caret being moved?
Note:
1) I don't want to use setCaretPosition() to set the caret to its original position, because calling this method will trigger a CaretEvent, thus causing the JScrollPane to scroll (to the caret) which is not what I want (see above).
2) I don't want to remove the CaretListener, cause then the JScrollPane won't scroll even when the user wants to make a multiple-page selection using the mouse (dragging the selection off screen).
3) I want to keep the Caret at the original position so that the user won't lose his/her selection when new messages appear (which can be quite frequent).

Answer 1

I keep forgetting how difficult it is to do such simple things in the text package. But it's not impossible! Here's a way to replace the relevant listeners, plus a sample implementation. If you know you'll never, ever delete any text from the JTextPane, you may not have to provide a replacement DocumentListener at all; this one just makes sure the caret isn't past the end of the document.
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.swing.text.DefaultCaret;
import javax.swing.text.Document;
import javax.swing.text.JTextComponent;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
public class ChatCaret extends DefaultCaret
  private MyHandler newHandler;
  private PropertyChangeListener oldHandler;
  public void install(JTextComponent c)
    super.install(c);
    PropertyChangeListener[] pcls = c.getPropertyChangeListeners();
    for (int i = 0; i < pcls.length; i++)
      if (pcls.getClass().getName().equals(
"javax.swing.text.DefaultCaret$Handler"))
oldHandler = pcls[i];
newHandler = new MyHandler(oldHandler);
c.removePropertyChangeListener(oldHandler);
c.addPropertyChangeListener(newHandler);
break;
Document doc = c.getDocument();
if (doc != null)
doc.removeDocumentListener((DocumentListener)oldHandler);
doc.addDocumentListener(newHandler);
public void deinstall(JTextComponent c)
super.deinstall(c);
c.removePropertyChangeListener(newHandler);
Document doc = c.getDocument();
if (doc != null)
doc.removeDocumentListener(newHandler);
class MyHandler implements PropertyChangeListener, DocumentListener
private PropertyChangeListener oldHandler;
MyHandler(PropertyChangeListener oldHandler)
this.oldHandler = oldHandler;
public void propertyChange(PropertyChangeEvent evt)
Object oldValue = evt.getOldValue();
Object newValue = evt.getNewValue();
if ((oldValue instanceof Document) ||
(newValue instanceof Document))
setDot(0);
if (oldValue != null)
((Document)oldValue).removeDocumentListener(this);
if (newValue != null)
((Document)newValue).addDocumentListener(this);
else
oldHandler.propertyChange(evt);
public void removeUpdate(DocumentEvent evt)
int length = getComponent().getDocument().getLength();
if (length < getDot())
setDot(length);
public void insertUpdate(DocumentEvent evt) { }
public void changedUpdate(DocumentEvent evt) { }