[Servlet] Basic method
doGet () method h1>
Describe the process to be executed at the time of GET request
doPost () method h1>
Describe the process to be executed at the time of POST request
init () method h1>
Describe the process to be executed immediately after the instance of the Servlet is created (at the first request to the Servlet).
Example of use)
-Initialization process of class used in Servlet