Question

I am having a problem with a .jsp page I am creating. For those worried, the site was for homework, however, I am trying to go beyond what is required and am not asking anything related to grading. This is strictly for my own benefit.

Down to business:
I am getting an input from the user, performing a method=”post” and refreshing the page, and in an ideal situation it works (that was the homework.) However, I am trying to make a try/catch block in the case where a user enters a string into an int field.

int Svolt = 0;
double Amperes = 0.0;
double LEDdrop = 0.0;

if (request.getParameter("Svolt") != null) {
try {
    Svolt = Integer.parseInt(request.getParameter("Svolt")); 
} catch ( NumberFormatException e ) {
    %>
    <script type ="text/javascript">
        alert("The source voltage must be an integer. Please fix this.");
    </script>
    <%                                                    
}

I’ve tried switching “NumberFormatException” to “Exception”, but it returned the same error code.
Earlier, I had my try catch come before the if() statement, and it worked, but didn’t display the alert box I want.

That code is below:

final double MA_TO_A = 0.001;
int Svolt = 0;
double Amperes = 0.0;
double LEDdrop = 0.0;

try {
    if (request.getParameter("Svolt") != null) {
        try {
            Svolt = Integer.parseInt(request.getParameter("Svolt"));
        } catch (Exception e) 
        {
            %>
            <script type ="text/javascript">
                alert("The source voltage must be an integer. Please fix this.");
            </script>
            <%
        }
        Amperes = Double.parseDouble(request.getParameter("Amperes"));
        LEDdrop = Double.parseDouble(request.getParameter("LEDdrop"));

        out.println("Ideal resistance is: " + ((Svolt - LEDdrop) / (Amperes * MA_TO_A)) + " Ohms.");   
    }
} catch (Exception e) {
        out.println("Please make sure your inputs are correct.");
}

Any help is appreciated, and your time is, too. Thank you very much!

EDIT:
Sorry, meant to copy-paste the error code:

org.apache.jasper.JasperException: java.lang.NumberFormatException: For input string: "a"

Where the tested input was the string “a”

EDIT2:
Back-up/edit/test @Nambari’s suggestion

final double MA_TO_A = 0.001;
int Svolt = 0;
double Amperes = 20.0;
double LEDdrop = 1.8;

try {
    if (request.getParameter("Svolt") != null) {
        try {
            Svolt = Integer.parseInt(request.getParameter("Svolt"));
        } catch (Exception e) 
        {
            %>
            <script type ="text/javascript">
                alert("The source voltage must be an integer. Please fix this.");
            </script>
        <%
        }
        out.println("Ideal resistance is: " + ((Svolt - LEDdrop) / (Amperes * MA_TO_A)) + " Ohms.");   
    }
} catch (Exception e) {
    out.println("Please make sure your inputs are correct.");
}

Output:
Ideal resistance is: -90.0 Ohms

Alert box saying (“The source voltage must be an integer. Please fix this.”)

No error code.

No out.println saying (“Please make sure your inputs correct”).

FINAL EDIT:

Code now works almost as desired, but good enough.

                    final double MA_TO_A = 0.001;
                    int Svolt;
                    double Amperes;
                    double LEDdrop;

                    if (request.getParameter("Svolt") != null) 
                    {
                        try 
                        {

                            try 
                            {
                                Svolt = Integer.parseInt(request.getParameter("Svolt"));
                            } catch (Exception e) 
                            {
                            %>
                            <script type ="text/javascript">
                                alert("The source voltage must be an integer. Please fix this.");
                            </script>
                            <%  
                            Svolt = 0;
                            }
                            try 
                            {
                                Amperes = Double.parseDouble(request.getParameter("Amperes"));
                            } catch (Exception e) 
                            {
                                %>
                                <script  type = "text/javascript"> 
                                    alert("The source voltage must be an integer. Please fix this.");
                                </script> 
                                <% 
                                Amperes = 0.0;
                            }
                            try 
                            {
                                LEDdrop = Double.parseDouble(request.getParameter("LEDdrop"));
                            } catch (Exception e) 
                            {
                            %>
                                <script  type = "text/javascript"> 
                                    alert("The source voltage must be an integer. Please fix this.");
                                </script> 
                            <%
                            LEDdrop = 0.0;
                            }
                            out.println("Ideal resistance is: " + ((Svolt - LEDdrop) / (Amperes * MA_TO_A)) + " Ohms.");
                        } catch (Exception e)
                        { 
                            out.println("Please make sure your inputs are correct."); 
                        }   
                    }

Lots of jargon, I know, but that’s the end result. Somehow, this has it all working. Thank you to all who helped!

Answer 1

This is posted as answer based on my comments:

I would suggest remove everything except the Svolt related code on your form and try. I think something else messing up than this filed. Take a backup of existing code. Remove everything except Svolt and see, we can nail down the issue.

Make sure try/catch blocks are properly synched with code flow as suggested in above comments.