title: "request.getParameter" return "-1" for non-existing URL parameters
body: <p>I have used following, in a JSP file to retrieve URL parameter.This JSP file represent a web page with a form which I am validating with Struts validator.</p>
  
  <pre><code>&lt;% String tempVal= (String)request.getParameter("parm");%&gt;
  </code></pre>
  
  <p>When the form initially loads, the <code>tempVal</code> parameter's value is <code>null</code> if there is no URL parameter with the name <code>parm</code>.<br/>Then I submit the form with some invalid data in the form, and the come to the same page(After hitting <code>Validate</code> method in the <code>ActionForm</code> class) with validate error messages.
  <br/>But this time the <code>tempVal</code> parameter's value is <code>-1</code>.
  <br/>
  Following is my <code>Validate</code> method in the <code>ActionForm</code> class.</p>
  
  <pre><code>@Override
  public ActionErrors validate(ActionMapping mapping, HttpServletRequest request)
  {
      ActionErrors errors = null;
      errors = super.validate(mapping, request);
      String temp2 = request.getParameter("param3");
      if(temp2 == null){
          errors.add("some Error");
      }
      return errors;
  }
  </code></pre>
  
  <p>Any reason for this behavior ?
  Thanks in advance </p>