1.Explain Servlet life cycle in java.

• 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.

2.What is ServletConfig ?

• Request parameters are used by the servlet to receive data from client to process the request.
• Some specific data must be supplied to the servlet at the time of initialization of the servlet and this data is specific to the client.But data is not supplied by the client via request parameters
• Use initialization parameters to supply the data to the servlet at the time of initialization of the servlet. initialization parameters are set in deployment descriptor   (Web.xml).
• Servlet can access these parameters during the run time
• Request parameters change form Request to request 
• Initialization parameters change from servlet to servlet.

3. What is ServletContext?

• We can deploy multiple web applications in a servlet container.
• Each web application contains its own resources in a separate  environment. This environment called ad Web Application context or ServletContext.
• The resources belongs to the one web application context are not available to the other web application context.
• A Servlet context contains zero or more number of servlets. For every servlet object the container creates separate ServletConfig object.

4. Can we define a Constructor in servlet?

• Yes we can define a constructor in servlet but we can not call the constructor explicitly because servlet container will create the object of servlet so it will be called by the servlet container.

5. Can we call destroy() method inside init() method of a servlet. If yes what will happen?

• Yes we can call destroy() method inside a init() method.
• Actually container will call destroy() method if we call that method explicitly nothing will happen.
• If we override destroy() method and called from init(). method will be called and code will be executed.

6.What are the difference between GenericServlet and HttpServlet?

7.What are the differences between doGet() and doPost()?