Passing calculation result to JSP page

Question

Index.jsp takes two input number and after submit the request go to Operation.java. It has a radio button to select Operation. Both inputs and radio button are submitted to Operation.java.

<body>
    <h1>Easy way to do fast operation</h1>
    <form action="Operation">
        First number::<input type="text" name="firstno"></input></br></br>
        Second number::<input type="text" name="Secondno"></input></br></br>
        <input type="radio" name="option" value="add">Add</input>
        <input type="radio" name="option" value="substract">Subtract</input>
        <input type="radio" name="option" value="mul">Multiply</input>
        <input type="radio" name="option" value="divide">Divide</input>
        </br></br>
        <input type="submit" value="submit"/>
    </form>    
    <%if(request.getAttribute("res")!=null){%>                   
        The result is ::${res}
    <%}%>
</body>

Operation.java(Servlet) takes value from input button and do calculation based on the radio button click. It will calculate the result.

int result1=0;
int n1=Integer.parseInt(request.getParameter("firstno"));
int n2=Integer.parseInt(request.getParameter("Secondno"));
String radio=request.getParameter("option");
if(radio.equals("add"))
{
    result1=n1+n2;
}
 else if(radio.equals("substract"))
{
    result1=n1-n2;
}
else if(radio.equals("mul"))
{
    result1=n1*n2;
}

       request.setAttribute("res", result1);
        RequestDispatcher requestDispatcher =      request.getRequestDispatcher("index.jsp");
        requestDispatcher.forward(request, response);

After calculation I want to show the result on the index.jsp. How can I do that?

@gjman2 But I want to get the result after clicking on submit button. not before. In this case in Index Page I always get the result value. — ASHISH, Sep 19 '13 at 06:04
@gjman2 I know but only basic. can you change above scriptlet code into jstl — ASHISH, Sep 19 '13 at 07:16
i have made changes on your codes with jstl, but u must have jstl library in your project — gjman2, Sep 19 '13 at 07:48

score 1 · Answer 1 · edited May 23 '17 at 12:01

1

There are several ways to communicate between servelt and jsp.

1)Through request.

2)Through session.

In your case,request level communication is enough.Dealing with session is little tricky,especially when you are not aware what it do.

In your servlet

            int n1=Integer.parseInt(request.getParameter("firstno"));
            int n2=Integer.parseInt(request.getParameter("Secondno"));

Those twolines causes nullpointer exception. if they are null.

Put null checks.

Then change the form action,it might be <form action="/Operation">.

Then from there set result to that request as a attribute.

Dispatch to the same jsp

get the request attribute in jsp.

Print there.

request.setAttribute("name", "value");
request.getRequestDispatcher("/index.jsp").forward(request, response);

Read more :

edited May 23 '17 at 12:01

Community

1
1

answered Sep 19 '13 at 05:38

Suresh Atta

120,458
37
198
307

But I want the value of the result only after clicking submit button. Not before that. If I use this I have already a value before clicking submit button. – ASHISH Sep 19 '13 at 06:06
@ASHISH After clicking the button,then only servlet gets invoke right ? – Suresh Atta Sep 19 '13 at 06:07
yes after clicking button, servlet get invoked. But in index.jsp It store previous operation value. – ASHISH Sep 19 '13 at 06:11
How you are setting the vaule in jsp ??Can you please edit your post with what you are doing right now ? – Suresh Atta Sep 19 '13 at 06:14
I use only ${res} after submit button and in servlet request.setAttribute("res", result1); RequestDispatcher requestDispatcher = request.getRequestDispatcher("index.jsp"); requestDispatcher.forward(request, response); – ASHISH Sep 19 '13 at 06:16

score 1 · Answer 2 · answered Sep 19 '13 at 05:43

1

By rendering the desired output in the response. Servlet is a very thin wrapper around HTTP: you are processing an HttpRequest and producing an HttpResponse.

answered Sep 19 '13 at 05:43

Rob

11,446
7
39
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Passing calculation result to JSP page

2 Answers2