HttpServlet error in eclipse

Question

I started learning Java recently and I am facing lot of simple but irritating issues. I spent a lot of time trying to figure out the problem in vain.

I am trying to run a simple registration (with 3 pages) and submit the values into a DB. I am getting `NullPointerException` and not sure how to proceed with debugging any help will be greatly appreciated.

`form1.html`

Form details:

    <!DOCTYPE html>
    <html>
    <head>
    </head>
    <body>
        <form action="./registration" method="get">
                Name:<input type="text" name="name"><br/> 
        Father Name: <input type="text" name="fname"><br/> 
        Mother Name: <input type="text" name="mname"><br/> 
                     <input type="hidden" name="formd" value="1"/>
                     <input type="submit" value="Next>>>">
        </form>
    </body>
    </html>

`form2.html`

    <!DOCTYPE html>
    <html>
    <head>
    </head>
    <body>
    <form action="./registration">
        Contact:<input type="text" name= "contact"><br/>
        Email: <input type= "text" name= "email"><br/>
        Address: <input type ="text" name= "address"><br/>
        <input type="hidden" name= "formd" value="2"/>
        <input type= "submit" value="Next>>>">
    </form>
    </body>
    </html>

`form3.html`

    <!DOCTYPE html>
    <html>
    <head>
    </head>
    <body>
    <form action="./registration">
        Qualification:<input type="text" name= "qualification"><br/>
        Percentage: <input type ="text" name= "percentage"><br/>
        <input type="hidden" name= "formd" value="3"/>
        <input type= "submit" value="Submit!">
    </form>
    </body>
    </html>

**My Servlet**

    package controller;

    import java.io.IOException;
    import java.io.PrintWriter;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.PreparedStatement;
    import java.sql.SQLException;

    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;

    public class AadharRegistration extends HttpServlet {
        private static final long serialVersionUID = 1L;

        protected void doGet(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
            PrintWriter out = response.getWriter();

            HttpSession httpsession = request.getSession();
            String fno = request.getParameter("formd");

            if (fno.equals("1")) {
                String name = request.getParameter("name");
                String fname = request.getParameter("fname");
                String mname = request.getParameter("mname");

                httpsession.setAttribute("name", name);
                httpsession.setAttribute("fname", fname);
                httpsession.setAttribute("mname", mname);

                response.sendRedirect("./form2.html");
            }

            if (fno.equals("2")) {
                String contact = request.getParameter("contact");
                String email = request.getParameter("email");
                String address = request.getParameter("address");

                httpsession.setAttribute("contact", contact);
                httpsession.setAttribute("email", email);
                httpsession.setAttribute("address", address);

                response.sendRedirect("./form3.html");

            }

            if (fno.equals("3")) {

                String qualification = request.getParameter("qualification");
                String percentage = request.getParameter("percentage");

                String name = (String) httpsession.getAttribute("name");
                String fname = (String) httpsession.getAttribute("fname");
                String mname = (String) httpsession.getAttribute("mname");

                String contact = (String) httpsession.getAttribute("contact");
                String email = (String) httpsession.getAttribute("email");
                String address = (String) httpsession.getAttribute("address");

                try {
                    Class.forName("oracle.jdbc.OracleDriver");
                    Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:p1aor01", "system",
                            "sysdba");

                    PreparedStatement ps = conn.prepareStatement("insert into aadhar values (?,?,?,?,?,?,?,?)");
                    ps.setString(1, name);
                    ps.setString(2, fname);
                    ps.setString(3, mname);
                    ps.setString(4, contact);
                    ps.setString(5, email);
                    ps.setString(6, address);
                    ps.setString(7, qualification);
                    ps.setString(8, percentage);

                    int res = ps.executeUpdate();

                    if (res != 0) {
                        out.println("<font color='green'><h1>Registered Successfully!</h1>");
                    }

                } catch (SQLException e) {
                    out.println("<font color='red'><h1>Registration exception Failed!</h1>");
                    e.printStackTrace();
                } catch (ClassNotFoundException xe) {
                    xe.printStackTrace();
                }
            }
        }

    }

I forgot to add Web.xml. please see below. If i use Dynamic web module version 3.1,i read that we do not need web.xml. Can i still use it? http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5"> TestAadharRegistration AadharRegistration AadharRegistration controller.AadharRegistration AadharRegistration /registration

**Error:**

    java.lang.NullPointerException
        controller.AadharRegistration.doGet(AadharRegistration.java:26)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)


    Note The full stack trace of the root cause is available in the server logs.

    From Console in eclipse:
    SEVERE: Servlet.service() for servlet [AadharRegistration] in context with path [/TestAadharRegistration] threw exception
    java.lang.NullPointerException
        at controller.AadharRegistration.doGet(AadharRegistration.java:26)

Can you post the URL you see on address bar after submission, and contents of web.xml where this servlet is registered.. — Vasan
Also, the code is for a http get method, but the html is a post. — Andrew S
@AndrewS The default form method is GET. Also, it does enter the doGet() method so.. — Vasan

Jonathan Laliberte Jonathan Laliberte · Accepted Answer · 2018-05-14T18:43:06

For some reason this line

 if (fno.equals("1")) {

is throwing the NullPointerException.

Which means your form is not sending the value. i.e. This is null:

String fno = request.getParameter("formd");

Before doing various operations on data, it's important to check if it is null. Otherwise you will get a NullPointerException if it is null. You can check for null like this:

if(fno != null && fno.equals("1")){

In this case, you'll need to find out why fno is null, because it shouldn't be if you have sent the value via the form. This is where browser developer tools can be useful.

If you're in Chrome, right click on your page and click "inspect".. Then click on the network panel. Now make sure you have checked the "Preserve log" checkbox at the top and then submit the form again. You will see a bunch of things happening, click on the one with your URL on it and then look at the headers. Scroll down and there will be a section called "Query String Parameters", here you can see what your form is sending to your servlet. If "formd" is not there, then that is why you are getting a NullPointerException.

HttpServlet error in eclipse

2 Answers