title: validate url with regular expressions
body: <p>I've gone through all possible ways for having the regular expression for the url validation,
  but I didn't get any..
  what I need is the url can be like</p>
  
  <pre><code>google.com
  http://google.com
  https://google.com
  http://www.google.com
  https://www.google.com
  </code></pre>
  
  <p>but it should not allow if it is just <code>google</code></p>
  
  <p>finally the thing is the <code>.extensions</code> are mandatory</p>
  
  <p>I've tried this <code>/^[a-z0-9-]+(.[a-z0-9-]*)(.[a-z0-9-]*)$/</code></p>
  
  <p>can anyone help me in this case..</p>