request.getAttribute returning null in servlet

Question

In jsp I have written following code:

    <form action="./ssoServlet?from=amount" method="post">
    <%request.setAttribute("formName", "DayCareForm"); %>
    Amount  
     <input type="text" name="amount" id="amount" required >
     <button onclick="dayCarePdf()" type="submit"> Convert to PDF </button>
    </form>

Post method of servlet is:

@Override
    public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("DoPost method");
        resp.setContentType("text/html");

        if(req.getParameter("from").equals("amount"))
        {
            req.getParameter("amount");

            String form = (String) req.getAttribute("formName");
            System.out.println("Type of form " +req.getAttribute("formName"));
            RequestDispatcher dispature = getServletContext().getRequestDispatcher("/DayCare.jsp");
            dispature.forward(req, resp);
        }
}

However, The servlet is returning null value for type of form

in your daycare() write below code document.getElementById("YOUR FORM ID ").submit(); and remove this ?from=amount — KhAn SaAb, Aug 29 '16 at 12:51
because onClick will directly go to the dayCare() function it wont sumbit a form. — KhAn SaAb, Aug 29 '16 at 12:52

Davide Lorenzo MARINO · Answer 1 · 2016-08-29T12:47:27.487

1

In the jsp You set a value in the request. So it works only for the life of the request.

The servlet is invoked before passing to the jsp. So when the attribute is retrieved from the request in the servlet it doesn't exist yet.

Put it in the session and it works.

When you reach the line:

String form = (String) request.getAttribute("formName");

a code

req.setAttribute("formName", something)

has not been set for the current request.

The code

<%request.setAttribute("formName", "DayCareForm"); %>

is performed on the previous request. Each time you pass to the servlet the request attributes are reset.

But you can set an attribute and retrieve an attribute from the session. In this case it works because a session ends when the browser is closed or the session is invalidated.

To work with a session, instead of a request replace

<%request.setAttribute("formName", "DayCareForm"); %>

with

<%session.setAttribute("formName", "DayCareForm"); %>

and

String form = (String) request.getAttribute("formName");

with

String form = (String) request.getSession().getAttribute("formName");

edited Aug 29 '16 at 12:47

answered Aug 29 '16 at 12:43

Davide Lorenzo MARINO

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Could u please support your answer with code – Radhika Kulkarni Aug 29 '16 at 12:44
I understood the problem now. So now i should add session.getAttribute("formName") ? – Radhika Kulkarni Aug 29 '16 at 12:54
@RadhikaKulkarni Yes, as you can see in the bottom part of the answer. – Davide Lorenzo MARINO Aug 29 '16 at 12:59
I have changed my code to whatever u have suggested. But i am still getting null – Radhika Kulkarni Aug 29 '16 at 12:59
@RadhikaKulkarni The code of the jsp is executed before the Servlet? In the jsp you set the attribute formName (in the session, not in the request)? – Davide Lorenzo MARINO Aug 29 '16 at 13:00
Yes. Jsp is executed first. In jsp i set attribute formName – Radhika Kulkarni Aug 29 '16 at 13:03
@RadhikaKulkarni are you sure that you set it on the session? – Davide Lorenzo MARINO Aug 29 '16 at 13:04
Yes i have changed it – Radhika Kulkarni Aug 29 '16 at 13:05
@RadhikaKulkarni have you redeployed the war? Jsp modification are taken also without redeploying the war, but servlet modifications are not. – Davide Lorenzo MARINO Aug 29 '16 at 13:10
type casting is not a solution.earlier she has not submitting the form. – KhAn SaAb Aug 29 '16 at 13:14
Hey!Thanx a lot.. I have used hidden value method and it worked – Radhika Kulkarni Aug 29 '16 at 13:17

KhAn SaAb · Accepted Answer · 2016-08-29T13:17:47.467

0

Try below code:

<form action="./ssoServlet" method="post" id="myForm" name="DayCareForm">
Amount  
 <input type="text" name="amount" id="amount" required >
 <input type="hidden" name="formName" value="DayCareForm" />
<button onclick="dayCarePdf()" type="submit"> Convert to PDF </button>
</form>

JavaScript:

function dayCarePdf()
{
    document.getElementById("myForm").submit();

//Rest Code will come here


}

set a hidden field as form name and you can access form name by below code.

   String formName= request.getParameter ("formName");  // you will get DayCareForm as we set form name

edited Aug 29 '16 at 13:17

answered Aug 29 '16 at 12:44

KhAn SaAb

5,248
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Submit is a button and not textfield – Radhika Kulkarni Aug 29 '16 at 12:46
but in your code i can see text box only, not a button, try my code – KhAn SaAb Aug 29 '16 at 12:46
I want the "formName" in servlet and not javascript – Radhika Kulkarni Aug 29 '16 at 13:00
check you can get form name by setting hidden field in form – KhAn SaAb Aug 29 '16 at 13:05
But it will add a textfield in my form. – Radhika Kulkarni Aug 29 '16 at 13:10
it doesn't matter its also a way to send some hidden value to servlet. its recommended – KhAn SaAb Aug 29 '16 at 13:11
setting attribute and sending hidden text value is same way. – KhAn SaAb Aug 29 '16 at 13:12
Yes!It worked ... Added the hidden field – Radhika Kulkarni Aug 29 '16 at 13:16
Great, if it works then please accept my answer. :) – KhAn SaAb Aug 29 '16 at 13:16
Accept my answer by selecting tick symbol over up and down arrow. – KhAn SaAb Aug 29 '16 at 13:22
There is an tick symbol to accept the answer, you require 15 reputation to upvote the answer, for accepting answer you wont require reputation. – KhAn SaAb Aug 29 '16 at 13:25
good, let me know if you face any issue in future I'm also from pune. :) good luck then – KhAn SaAb Aug 29 '16 at 13:27

request.getAttribute returning null in servlet

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