Preview:
index.html:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Add numbers</title>
</head>
<body>
	
	<form action="add" method="get">
		enter num1:<input type="text" name="num1"><br>
		Enter num2:<input type="text" name="num2">
		
		<br>
		<input type="submit" value="Add">
	</form>
</body>
</html>

Add.java:
package com.Add;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet( urlPatterns={"/add"})
public class Add extends HttpServlet {
    public void service(HttpServletRequest req, HttpServletResponse res) throws IOException {
    	
    	int i=Integer.parseInt(req.getParameter("num1"));
    	int j=Integer.parseInt(req.getParameter("num2"));
    	
    	int k=i+j;
    	PrintWriter out=res.getWriter();
    	out.println(k);
    			
    }

}

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_4_0.xsd" id="WebApp_ID" version="4.0">
  <display-name>ParamDemo</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.jsp</welcome-file>
    <welcome-file>default.htm</welcome-file>
  </welcome-file-list>
</web-app>
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