Servlet Life Cycle

Servlet Life Cycle went through three main methods and all three main methods called by Servlet Engine or Web container.
The methods are:
1. init()
2. Service()
3. Destroy()

1 -init() : init() method of a servlet is called only once in its lifecycle, when a very first request comes to servlet it makes servlet state from does not exists to initialized state and during all other requests servlet remains already initialized.

The container calls the init() method before the servlet can serve any client request. This method can be overridden in our servlet classes to write some initialization code in it. Initialization means something like initializing your data source or other things that we want ready before servlet starts serving the request. 

2 -service() : Service methods are the methods where actual working of servlet is defined, a service method is called every time a request comes for a servlet. It determines which http method should be called based on client request. There are 7 http methods but almost in 99% of web application you will be dealing with either a doGet() or a doPost() method.

If user request is a get request than doGet() method of servlet is called and if the request ia a post than doPost() method is called and all the business logic goes into either a doGet() or a doPost() method of servlet.  

3 -destroy() : This method is called by the container when the servlet is no longer required.