title: How to limit a JTextArea to only accept a legal set of characters?
body: <p>Anybody know if there is an easy way to limit the allowed characters for a JTextArea. I.e. similar to JTextField using MaskFormatter.</p>
  
  <p>Specifically I want to limit the allowed characters for a JTextArea to only uppercase characters and only a very limited set characters like !"#¤%&amp;/()=</p>