JScrollPane Scroll Position

Question

Tried posting this in the newbie section with no luck....
I created a class extending a JScrollPane that encompasses a JTextPane. The method below appends some text to the current JTextPane with a certain color (this part works fine). What I am also trying to do is force the JScrollPane to keep focus at the bottom after the append if it was there before the append. Now I am running into trouble.
The code can determine fine if the scroll pane is at the end, but after the append, it sometimes prematurely puts the pane at the end again; i.e. the method is telling the scroll pane to go to the end before the text pane and/or scroll pane have finished updating their size. Thus, the scroll pane is moved to the bottom, then the text and scroll panes resize, and the scroll pane is no longer at the bottom.
It seems that this problem occurs when the text appended is multiple lines, in which case it appears that the panes are resized multiple times- the scroll bar is positioned correctly after the first resize, but subsequent resizings sometimes occur after I reposition the scroll bar to the current "end" (which then changes).
I've tried validating both panes to force them to update before repositioning the scroll bar, but this does not seem to stop the problem (although it may help).
Does anyone know how to correct this problem? I'm still guessing that something (perhaps the doc?) is not fully updated by the time I reposition the scroll bar. If this is the problem, any suggestions on how to force the document to be updated before playing with these GUI panes? If possible, I prefer not to use a timer or sleep a thread to wait for this updating.
Of course, if you know of existing methods/settings that help with this, please tell. I didn't manage to find anything in the API's that gave me what I want, but I've been known to overlook things from time to time ;)
Again, this is a method in a class extending JScrollPane.
textPane is the JTextPane embedded in the scroll pane.
doc is the JTextPane document.
public synchronized void append(String appendString, Color textColor)
     JScrollBar scrollBar;
     BoundedRangeModel rangeModel;
     boolean isMaxed;
     scrollBar = this.getVerticalScrollBar();
     rangeModel = scrollBar.getModel();
     isMaxed = ((rangeModel.getValue() + rangeModel.getExtent())
                         == rangeModel.getMaximum());
          // check if the scroll bar is at the bottom
     SimpleAttributeSet textAttributes = new SimpleAttributeSet();
     StyleConstants.setForeground(textAttributes, textColor);
     try
          doc.insertString(doc.getLength(), appendString, textAttributes);
          // append the formatted string to the document
     catch(BadLocationException ex)
          System.out.println("Error writing to the text pane");
     if (isMaxed)
          textPane.validate();     //force the text pane to validate
          this.validate();    //force the scroll pane to update
          scrollBar.setValue(rangeModel.getMaximum() - rangeModel.getExtent());
          // The above line is sometimes called before the text and scroll panes
          // have finished updating.  The maximum and extent of the scroll bar
          // depend on the size of the document.

Answer 1

You are correct in your observation that the size of the JScrollPane is incorrectly reflected for the size of your newly appended document. I spent some time on this bug and eventually came up with the following solution:
textPane.addComponentListener( new ComponentListener(){
public void componentHidden(ComponentEvent e)
public void componentMoved(ComponentEvent e)
public void componentResized(ComponentEvent e)
JViewport vp = scrollPane.getViewport();
incoming.revalidate();
Rectangle visRect = vp.getViewRect();
Dimension viewDim = vp.getViewSize();
Rectangle rect = new Rectangle( 0, (int)(viewDim.getHeight() - visRect.getHeight()),
(int)visRect.getWidth(), (int)visRect.getHeight() );
vp.scrollRectToVisible( rect );
public void componentShown(ComponentEvent e )
This solution also has the side benefit of scrolling to the bottom when the JTextPane is resized by the user.