display second popup form window automatically after first popup form is submitted successfully

I have a pop up register form on the "index.jsp" page. So, if a user fills the register form and submits it, it goes to a servlet and the fields in the form are inserted into a database. After this is processed with no errors, i want a login pop up to show automcatically in the same page, without any links being clicked. How can i do this?

the following is the link that pop's up a register form:

<a id="modal_trigger" href="#modal"><span>Register</span></a>

the following is the div class specifications:

#lean_overlay {
    position: fixed;
    z-index:100;
    top: 0px;
    left: 0px;
    height:100%;
    width:100%;
    background: #000;
    display: none;
}

.popupContainer{
    position:absolute;
    width:330px;
    height: auto;
    left:45%;
    top:0px;
    background: #FFF;
    margin-top: -50px;

}

#modal_trigger {}

the following is the request dispatcher:

rd = request.getRequestDispatcher("**What link should be here???**?");
rd.forward(request, response);

the following is the javascript for the popup form:

$("#modal_trigger").leanModal({top : 200, overlay : 0.6, closeButton: ".modal_close" });

  $(function(){
    // Calling Login Form
    $("#login_form").click(function(){
      $(".user_login").show();
      return false;
    });
    // Calling Register Form
    $("#register_form").click(function(){
      $(".user_login").hide();
      $(".user_register").show();
      $(".header_title").text('Register');
      return false;
    });

    // Going back to Social Forms
    $(".back_btn").click(function(){
      $(".user_login").show();
      $(".user_register").hide();
      $(".header_title").text('Login');
      return false;
    });

  })