Servlet not able to get input

Question

I am trying to create a program in which I can accept input and get the square root of a number with a servlet. I am a beginner, so I don't know much. The problem is when I try my code, it doesn't work. Here is the code:

MyServletDemo.java

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.lang.Math;

public class MyServletDemo extends HttpServlet {

     public void init() throws ServletException {
    }
   protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
   }
   public void doGet(HttpServletRequest request, 
      HttpServletResponse response)
      throws ServletException, IOException 
   {


      response.setContentType("text/html");
      String num2 = request.getParameter("num");
      int num3 = Integer.parseInt(num2); //This is where the error
      int numSqrt = Math.sqrt(num3);
      PrintWriter out = response.getWriter();
      out.println("<p> The sqrt is "+numSqrt+"</p>");
   }

}

index.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!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=ISO-8859-1">
<title>Get sqrt of num</title>
</head>
<body>


    <p>Num to find sqrt of: </p> <input type="text" name="num"/>


    <a href="welcome">Click to call Servlet</a>


</body>
</html>

I don't know much about xml, I found the code in a tutorial: web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>Find-the-sqrt-of-num</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>

<servlet>
<servlet-name>MyHttpServletDemo</servlet-name>
<servlet-class>MyServletDemo</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>MyHttpServletDemo</servlet-name>
<url-pattern>/welcome</url-pattern>
</servlet-mapping>

</web-app>

The results are: First this, then when you hit the link, you get :

This result

You need a form and a POST. – user207421 Jan 09 '20 at 05:14 — user207421, Jan 09 '20 at 05:14

Patrick Tolentino · Answer 1 · 2020-02-06T01:34:53.667

2

What you need to do is make a POST request to your servlet instead of GET. The idea is if you need to pass information to your servlet, you are POSTING information to your server.

If you don't specify the method type in your jsp, it defaults to GET and GET is used for just moving to different pages of your website without passing/submitting information to your server(servlet)

Take time to know the basic differences of GET and POST requests for a servlet.

In your code, after the tag, you need to wrap all tags inside with a <form> tag and set the attribute of "method" to POST type. In your servlet, instead of doGet() use the doPost() method.

You can find many samples from google of a simple POST request using jsp and servlet.

edited Feb 06 '20 at 01:34

answered Jan 09 '20 at 04:50

Patrick Tolentino

79
1
8

How do I give the request value to GET? When I try to put the code into POST, it throws an error. – Nefarious Jones Jan 10 '20 at 02:27
What changes did you make this time? And what error are you seeing differently after your changes? – Patrick Tolentino Jan 10 '20 at 03:28

score 1 · Accepted Answer · answered Jan 09 '20 at 04:18

1

You are getting null error because request.getParameter("num") is null .In your jsp page you never send any value to your servlet i.e : by writing <a href="welcome">Click to call Servlet</a> this will take you to the servlet but will not send any parameter with it .Instead do like below:

 <form method="get" action="Yourservletpage">
   <p>Num to find sqrt of: </p> <input type="text" name="num"/>
   <input type="submit" name="submit" value="submit" />
 </form>

answered Jan 09 '20 at 04:18

Swati

28,069
4
21
41

Do I put "Yourservletpage" in action, or do I put "MyServletDemo"? – Nefarious Jones Jan 10 '20 at 02:36
You need to put your servlet name i.e`MyServletDemo` – Swati Jan 10 '20 at 04:03
What do I put in the JSP page? – Nefarious Jones Jan 12 '20 at 00:09
only above code and servlet will remain same no changes needed to make . – Swati Jan 12 '20 at 15:14
I put the code, but it gave this error: The origin server did not find a current representation for the target resource or is not willing to disclose that one exists. – Nefarious Jones Jan 13 '20 at 00:26
In your `action` put `action="/welcome"` ,also check [this](https://stackoverflow.com/questions/43186315/tomcat-404-error-the-origin-server-did-not-find-a-current-representation-for-th) post. – Swati Jan 13 '20 at 04:59
It still gives this error: The origin server did not find a current representation for the target resource or is not willing to disclose that one exists. – Nefarious Jones Jan 18 '20 at 17:22

score 1 · Answer 3 · answered Jan 09 '20 at 04:30

1

Or try this:

<a href="welcome?num=123">Click to call Servlet</a>

answered Jan 09 '20 at 04:30

ErShakirAnsari

653
7
19

What do I write in the servlet? – Nefarious Jones Jan 10 '20 at 02:24
For that matter, what do I put to replace "123" to make it interactive? – Nefarious Jones Jan 10 '20 at 02:56
It is the link in your `index.jsp` – ErShakirAnsari Jan 10 '20 at 04:18
What does that mean? – Nefarious Jones Jan 12 '20 at 01:40

Servlet not able to get input

3 Answers3