Preview:
Add.java
@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);
    			
    }

}

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>
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