title: To disable/enable a button submit in a form
body: <p>I have a form (in a JSP file) with:</p>
  
  <ul>
  <li><p>A <strong>textarea</strong> named <strong>textarea1</strong>.</p></li>
  <li><p>A button type submit.</p></li>
  </ul>
  
  <p>I do this:</p>
  
  <pre><code>... // My form.
  String text=request.getParameter("textarea1"); 
  if(text!=null){
    ... // ???? 
    ... // Code.
    ... // ????
  }
  </code></pre>
  
  <p>I need to disable my button submit and enable it after (see the comments '????'). Another valid option for me (I think) is blocking and unblocking all my form (textarea and button). How can I do these (disable/enable the button and block/unblock the form)?</p>