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HttpSession session = request.getSession(true);


/*User class is a Java bean with an isValid attribute*/
  User user= new User();
  if (!user.isValid()) {
         request.setAttribute("errorMessage"," Invalid Parameters!");
         request.getRequestDispatcher("RegistrationPage.jsp").forward(request, response);
  }


// RegistrationPage.jsp file code snippet is below


<script>
function loginFailure() {
           System.out.println("Invalid parameters");
           if(request.getParameter("errorMessage") != null) {
              alert("<%= request.getParameter("errorMessage") %>");
           }

</script>

<body onload="loginFailure()">
</body>

<script>
function loginFailure() {<%
           if(request.getParameter("errorMessage") != null) {
               System.out.println("Invalid parameters");
               %>
               alert("<%= request.getAttribute("errorMessage") %>");
               <%
           }%>
</script>

Scriptlet and javascript to display this message:

<%
            String message = (String) request.getAttribute("errorMessage");
            if (message != null) {
            %>
              <script>
                   alert('<%=message%>');
              </script>
           <%
            }else{

            %>
            <script>
                 alert("Login Successfull");

            </script>
        <%
            }
        %>