passing data from jsp to servlet using mvc and jdbc

Im currently new in java ee. I need help on how to pass my data from jsp to my servlet to fil up my query. Whenever i run, the error is being catch and i print out the exception. It says java.null.exception.. I couldn't find out where my error is..please help me... thanks..

Here is my code:

UpdateProductServlet.java

and my ProductDao.java

and this is my ProductById.jsp

<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
        <script>
            function functionEdit()
            {
                document.getElementById("edit").type="hidden";
                document.getElementById("update").type="button";
                document.getElementById("delete").type="hidden";
                document.getElementById("cancel").type="button";
                
                document.getElementById("description").disabled="";
                document.getElementById("size").disabled="";
                document.getElementById("price").disabled="";
                document.getElementById("select").disabled="";
            }
            
            function functionUpdateRecord(){
                if(confirm('Update existing record?')){
                    document.location.href="/MachineProblemWebApp/UpdateProductServlet";
                    alert('Update success!');
                    document.location.href="/MachineProblemWebApp/GetAllProductsServlet";
                    
                }else{ 
                    alert('No changes have been made!');
                }

}
            
        </script>
    </head>
    <body>
        <table border="0">
            <tr>
                <td>id: </td>
                <td><input type="text" name="id" id="id" value="${product.id}" disabled="disabled"></td>
            </tr>
            <tr>
                <td>Description: </td>
                <td><input type="text" name="description" id="description" 
                                                value="${product.description}" disabled="disabled"></td>
            </tr>
            <tr>
                <td>Aisle </td>
                <td><select name="aisle" disabled="disabled" id="select">
                        <c:forEach var="aisle" items="${aisles}" >
                            <option value="${aisle.id}" ${(aisle.id==product.aisle.id)?"selected" : ""}>
                                        ${aisle.description}
                            </option>
                        </c:forEach>
                    </select></td>
            </tr>
            <tr>
                <td>Size: </td>
                <td><input type="text" name="size" id="size" value="${product.size}" disabled="disabled"></td>
            </tr>
            <tr>
                <td>Price: </td>
                <td><input type="text" name="price" id="price" value="${product.price}" disabled="disabled"></td>
            </tr>
            <tr>
                <td><input type="button" name="edit" id="edit" onClick="functionEdit()" value="Edit" >
                    <input type="hidden" name="update" id="update" onClick="functionUpdateRecord()"value="Update">
                    <input type="button" name="delete" id="delete" value="Delete">
                    <input type="hidden" name="cancel" id="cancel" value="Cancel"></td>
            </tr>
        </table>

Any of your form inputs which are disabled do not get submitted, so they never reach the servlet as request parameters. Take out all the disabled attributes for the data you want to show up in the request.

Also you have this in your Servlet for error handling:

That is very bad practice: You should print the exception's message and stack trace to a log file at least, and not just the e.toString() to the page's output. That would help you figure out which parameter is null.

Hi. I have a button there when the edit button (javascript function)is click, the fields will be enabled allowing user to edit the fields except for the id. then the update button will appear for calling the servlet.

Hi,

I carefully read your code for servlets and jsp . My point of view null pointer exception error is run time error.

1) In UpdateProductServlet.java , your are not accessing all parameters from jsp page.

you can check all values whether these are coming or not. using followings statement

like as
System.out.println(description);
System.out.println(price);
System.out.println(size);
System.out.println(aisle_id);
System.out.println(id);

If any one above statements will display NULL or null , it means that no value is transfer from jsp to servlet.

hi. i have solve the problem, i forgot to include form action in my jsp..