how http method works in servlet?

I have a problem with my servlet. I have an HTML page where I call get method for a sum of two numbers when I submit my form it gave me an error. But I already declare get method in my servlet class.

Type: Status Report

Message: HTTP method POST is not supported by this URL

Description The method received in the request-line is known by the origin server but not supported by the target resource.

Servlet code:

public class AddServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        int a=Integer.parseInt(req.getParameter("num1"));
        int b=Integer.parseInt(req.getParameter("num2"));
        int sum=a+b;
        resp.getWriter().println(sum+ " doGet method");
    }
}

html code:

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Servlet</title>
  </head>
  <body>
    <form action="add" method="get" >
      Enter 1st number<input type="text" name="num1">
      Enter 2st number<input type="text" name="num2">
      <input type="submit">
    </form>
  </body>
</html>

deployment descriptor code: 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>ServletPractice1</display-name>
  <servlet>
    <servlet-name>AddServlet</servlet-name>
    <servlet-class>com.meet.servlet.AddServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>AddServlet</servlet-name>
    <url-pattern>/add</url-pattern>
  </servlet-mapping>
</web-app>

Solution

You do not have a valid doGet() method, when you type the servlet’s path in address bar directly, the web container like Tomcat will try to invoke the doGet() method.

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException{
    ....        
}

Or else Override service method like this:

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