java httpservlet getparameter from html returning null

Question

I am running a .jsp file on a server and trying to send user input form data to the "doPost" method in the HttpServlet.

When I try to print the vals of user input in doPost, they are null.

I am trying to get the vals by their html ID, but that's not working for some reason. There could be a simple issue in the HTML.

The submit button seems to be working as it is routing properly back to the .java file I am trying to parse the user input data with. It is only the vals that are null.

Here is my code.

Thank you! :)

<%@page import="java.util.Date"%>
<%@ page language="java" contentType="text/html; charset=US-ASCII"
    pageEncoding="US-ASCII"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Binary Encoder</title>
</head>
<body>

    <h2>Binary Encoding: Encode any number from 0 to 65535</h2> <br>
    <h3>Date=<%= new Date() %>
    </h3>

    <!-- in this form I need to figure out how to get user input into Binaryencoder.java-->
    <form action="../Binaryencoder" method="post">
        Input number you want to encode (0 to 65536):<br>
        <input type="number" id="toencode"><br>

        Input first number for encoding (0 to 255) :<br>
        <input type="number" id="mask1"><br><br>

        Input second number for encoding (0 to 255) :<br>
        <input type="number" id="mask2"><br><br>

        <input type="submit" id="submit" value="Submit">
    </form>


</body>
</html>

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {      
        doGet(request, response);

        //code to process the form... 
        String toencode = request.getParameter("toencode");
        String mask1 = request.getParameter("mask1");
        String mask2 = request.getParameter("mask2");

        //response is the thing that goes back to HTML page 
        PrintWriter out = response.getWriter();

        String output = String.format("Number to encode is: %s", toencode);
        String op1 = String.format("Mask1 is: %s", mask1);
        String op2 = String.format("Mask2 is: %s", mask2);

        out.println(output);
        out.println(op1); 
        out.println(op2); 

    }

prasad_ · Accepted Answer · 2018-12-21 02:29:33Z

2

The issue is with these tags, e.g.,: <input type="number" id="toencode"> The tag needs a name attribute, like this: name="mynumber"

The servlet receives the name-value pairs of the request parameters from the JSP. In your JSP the name is missing. The correct way to code your JSP is: <input type="number" id="toencode" name="mynumber">

In the servlet program access the posted parameter and its value as follows in the doPost method:

public void doPost(HttpServletRequest request, HttpServletResponse response)
        throws IOException, ServletException {
    String myNumber = request.getParameter("mynumber");
    getServletContext().log("# My Number: " + myNumber); // this prints in the log file
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    out.println("My Number: " + myNumber); // this prints on the browser page
}

This should show the number you had entered in the JSP in the browser page, like: My Number: 999. You can also refer the server logs.

answered Dec 21, 2018 at 2:29

prasad_

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1 Comment

prasad_ Over a year ago

Also, see these:<input type="number"> and HTML: Number Input Control.

ErShakirAnsari · Accepted Answer · 2018-12-21 05:29:30Z

2

Add name attribute to your input like below:

<input type="number" name="toencode" id="toencode">
<input type="number" name="mask1" id="mask1">
<input type="number" name="mask2" id="mask2">

request.getParameter does not recognize id attributes.

answered Dec 21, 2018 at 5:29

ErShakirAnsari

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Comments

mingle08 · Accepted Answer · 2018-12-20 23:36:46Z

1

The type of three input should be text, not number . try it.

answered Dec 20, 2018 at 23:36

mingle08

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2 Comments

Mukul K. Over a year ago

changed all types to "text", still didn't work. Are you sure it needs to be text? Im trying to input numbers in this form.

mingle08 Over a year ago

@MukulK. Maybe it's not the question, type of number is added in H5. Why you call doGet method here? You can delete it or cut the code below to doGet method.

hlg · Accepted Answer · 2018-12-21 00:52:48Z

1

In the three form input fields, use the name attribute instead of or in addition to id. Only the values of these input fields are included in the request as parameters.

edited Dec 21, 2018 at 0:52

answered Dec 21, 2018 at 0:46

hlg

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1 Comment

Mukul K. Over a year ago

this fixed my problem. Thanks so much !! : ) now I have user input in Java

blurfus · Accepted Answer · 2018-12-21 07:47:39Z

1

Your form seems to be missing the name attribute for all the fields.

Try changing this:

<input type="number" id="toencode">

to this (adding the name attribute to the toencode field):

<input type="number" id="toencode" name="toencode">

Obviously, for the other fields (mask1, mask2) the names value would be matching their ids

answered Dec 21, 2018 at 7:47

blurfus

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