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Cannot forward after response has been committed

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posted 15 years ago

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Hi, im kind of new to servlets. i have a servlet which accepts data from a HTML form. Basically 2 numbers, according to the option chosen, their addition,multiply etc. User enters the answer, servlet checks whether it was correct or not. If wrong, shows solution.
processRequest() is the function which is called by doPost. It calls processAnswer() which basically does the forwarding of the page according to the answer.
Heres processRequest

WHICH CALLS processAnswer()

public void processAnswer(int answer, int option, int num1, int num2, HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        switch (option) {
            case 1: {
                int temp = num1 + num2;//Addition
                if (answer == temp) {
                    String display = "<HTML><BODY>" +
                            "<h3>Your answer is correct! </h3>" +
                            "</BODY></HTML>";
                    request.setAttribute("result", display);
                    getServletContext().getRequestDispatcher("/levelone.jsp").forward(request, response);
                } else {
                    String display = generateAnswer(num1, num2, '+',temp); //THIS RETURNS JUST A STRING
                    request.setAttribute("result", display);
                    getServletContext().getRequestDispatcher("/levelone.jsp").forward(request, response);
                }
            }
            case 2: {
                int temp = num1 - num2; //Subtraction
                if (answer == temp) {
                    String display = "<HTML><BODY>" +
                            "<h3>Your answer is correct! </h3>" +
                            "</BODY></HTML>";
                    request.setAttribute("result", display);
                    getServletContext().getRequestDispatcher("/levelone.jsp").forward(request, response);
                } else {
                    String display = generateAnswer(num1, num2, '-',temp);
                    request.setAttribute("result", display);
                    getServletContext().getRequestDispatcher("/levelone.jsp").forward(request, response);
                }
            }
       }
}

Really need help here..I tried adding a "return" in processRequest, didnt help.

sudipto shekhar

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posted 15 years ago

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Hello and welcome to java ranch.

I am sorry, did not get your problem..
If "Cannot forward after response has been committed" is the problem then always remember that you can not forward the servlet/jsp to another one of a kind after you have committed the response to the client!! Remember that always, forward before you commit.

Hope this helps..

Regards, Sud.
SCJP 5 ScjpFAQ JLS

Seetharaman Venkatasamy

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posted 15 years ago

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Originally posted by Udayaditya Barua:

protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); //PrintWriter out = response.getWriter(); int answer = 0; int number1 = 0; int number2 = 0; int opt = 0; /*various getRequestParameters...*/ try { /*Converting strings to integers (parseInt)....*/ } catch (NumberFormatException nfe) { //In case user entered anything else other dan a number String display = "<HTML><BODY>" + "<h3>YOU ARE SUPPOSED TO ENTER A NUMBER!</h3>" + "</BODY></HTML>"; request.setAttribute("result", display); getServletContext().getRequestDispatcher("/levelone.jsp").forward(request, response); } [B]processAnswer(answer, opt, number1, number2, request, response);[/B] }

processAnswer(answer, opt, number1, number2, request, response);

why you put after catch ?...i guess first it enters catch and forward to some page agin it calls processAnswer and init once agin you are trying to forward .... instead you put your processAnswer(answer, opt, number1, number2, request, response); inside try block

Abhijit Rai

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Posts: 41

posted 15 years ago

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hi,
Do remember that in switch case once a condition is met in a case all the subsequent case blocks get executed ,hence the error .To make it work find
an alternative to switch case approach.Try using if ...else I think it might
work out

[ December 06, 2008: Message edited by: Abhijit Rai ]

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Udayaditya Barua

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posted 15 years ago

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@shekhar
thanks

Ok, sry for the delay.. Managed to solve the problem after a lot of searching... Had to write a 'return' after the forward command..
About the switch case executing every statement, doesnt writing a "break" solve that?..Just asking..

sudipto shekhar

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posted 15 years ago

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Yes of course. You know the fundamentals of switch case statement.....
By writing break you tell the program to come out after the case has matched....
Otherwise once a case is matched and break is not used then all the subsequent cases too are evaluated.... Hope this helps.

Regards, Sud.
SCJP 5 ScjpFAQ JLS

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