title: Regular Expression in Java for validating username
body: <p>I'm trying the username chains in Java with following rules:</p>
  
  <ul>
  <li>Length >=3</li>
  <li>Valid characters: a-z, A-Z, 0-9, points, dashes and underscores.</li>
  </ul>
  
  <p>Could someone help me with the regular expression? </p>