I have a JScrollPane with a JTextArea set as its view port.

I update the (multi line) text shown on the JTextArea continously about once a second. Each time the text updates, JScrollPane goes all the way to the bottom of the text.

Instead, I'd like to figure out the line number that is currently shown as the first line in the original text, and have that line be the first line shown when the text has been updated (or if the new text doesn't have that many lines, then scroll all the way to the bottom).

My first attempt of doing this was to get the current caret position, figure the line based on that, and then set the text area to show that line:

    int currentPos = textArea.getCaretPosition();
    int currentLine = 0;
    try {
        for(int i = 0; i < textArea.getLineCount(); i++) {
            if((currentPos >= textArea.getLineStartOffset(i)) && (currentPos < gameStateTextArea.getLineEndOffset(i))) {
                currentLine = i;
                break;
            }
        }
    } catch(Exception e) { }

    textArea.setText(text);

    int newLine = Math.min(currentLine, textArea.getLineCount());
    int newOffset = 0;
    try {
        newOffset = textArea.getLineStartOffset(newLine);
    } catch(Exception e) { }

    textArea.setCaretPosition(newOffset);

This was almost acceptable for my needs, but requires the user to click inside the text area to change the caret position, so that the scrolling will maintain state (which isn't nice).

How would I do this using the (vertical) scroll position instead ?