Java SE (Java Platform, Standard Edition)

I am fairly new to swing and I'm trying to make a text editor. One of the features i want to implement is a TAB and Shift+TAB indent feature. What I mean by this is the user selects a few lines and hits the tab key and indents the lines with the textArea.tabSize or vice versa with shift+tab. I already got the JTextArea to recognize tab and shift tab with this code (from another post):

InputMap im = textArea1.getInputMap();
KeyStroke tab = KeyStroke.getKeyStroke("TAB");
textArea1.getActionMap().put(im.get(tab), new TabAction(true));
KeyStroke shiftTab = KeyStroke.getKeyStroke("shift TAB");
im.put(shiftTab, shiftTab);
textArea1.getActionMap().put(im.get(shiftTab), new TabAction(false));

and obviously implementing the class TabAction. Inserting the tab isn't that difficult I use the Element class to get the lines position and insert 8 spaces or whatever its set to. My question is how can i get the shift+tab part to work obviously i will have to check if a tab exists on each line and then remove it.

Any sample code or ideas would be appreciated.