Servlet Life Cycle

Servlet life cycle Methods:

• Servlet engine controls the life cycle of servlet
• Servlet life cycle is described by three life cycle methods under 5 life cycle phases
• life cycle methods are

1. init(ServletConfig obj)
2. service(servletRequest, servletResponse)
3. destroy() 

When ever somethings happens in the life of servlet. servlet engine calls these methods on the servlet
instance and hence the name.

Life cycle phases :

1. Does not exist phase
2. Instantiation phase
3. Initialization phase
4. Servicing  phase
5. Destruction phase

Doesn't Exist:

• Servlet class is made available to the servlet engine but not yet its instance is created.
• It is known as doesn't exist phase of a servlet.

Instatiation:

• The process of creating the object of a class is known as instantiation.
• Servlet engine loads user user defined servlet class file from secondary memory into
  primary memory dynamically
  
  class c= class.forName("name");
  c.newInstance();
• Servlet engine creates the instance of loaded servlet class.
• Servlet engine uses the following piece of code to load the servlet clas  dynamically to instantiate it.
  Class c= class.forName("Servlet class name");
  c.newInstance();

Initialization:

• Servlet engine creates servletConfig object
• Servlet engine calls the init() method on the servlet instance by supplying servletconfig object
  as argument.
• Once init method completely executed servlet is ready to serve the client request.

Servicing : 

• Servlet engine creates servlet request and servlet response object based on the web server
  provided client information.
• Servlet engine calls service method on the servlet instance by supplying two object reference as arguments
• Once service method is completely executed , client request is served and request-response cycle is complete.
• Within the service method request object is used to capture the user input
• Response object is used to build the dynamic page and hand over the same to the web server

Destruction:

• Destruction phase of servlet represents servlet being removed from use by container