Servlet Life Cycle

 

Servlet Life Cycle:

When you deploy an application under web-app folder of tomcat home directory and start the tomcat (i.e. deploy the application in tomcat)

1.     Web container (tomcat) reads the Deployment Descriptor (web.xml) and creates a Servlet Context object.  

2.    Container reads the DD and search for <context- param> (if any) and creates a Key/value pair of Strings  for corresponding <param-name> and           

<param-value>.

Ex.  <context-param>

          <param-name>AdminEmail</pram-name>

          <param-value>susheel.nitdgp@gmail.com </param-value>

      </context-param>

Will create a reference with key as ‘AdminEmail’ and value as ‘susheel.nitdgp@gmail.com’

3.    This key/ value reference is provided to ServletContext reference.

4.    ServletContextListener (if any) will be called.

5.    Container will create ServletConfig Object.

6.    Container reads the DD and search for any servlet initialization parameters.

Ex. <servlet>

          <servlet-name>……..</servlet-name>

          <servlet-class>………</servlet-class>

          <init-param>

                   <param-name>…….</param-name>

                   <param-value>……..</param-value>

          </init-param>

     </servlet>

7.    The key value pair of Strings will be created for init parameters (same as for context param) and will be assigned to ServletConfig reference.

Note : no servlet is still created till this step even servlet life cycle is not started.

8.    Container will create request and response objects.

9.    Servlet class will be loaded by container.

10.   Servlet default no-arg constructor will be called and a simple java object is created(still we don’t have servlet object).

11.  First Life Cycle method for Servlet init(ServletConfig ) will be called and servlet object will be created and initialized.

12.  Container will start a thread and calls the Second life cycle method and most used method service(request, response) of the Servlet.

13. Service() method will call doGet(request, response) or doPost(request, response) method based on the submitted method name.

14.  Service() method is the place where all the work is done.

15.   An response is created by using getWriter() or getOutputStream() methods of Response object.

16.  Response is sent to any other servlet, jsp using Request Dispatcher or committed to client.

17.  In later case request, response objects will be destroyed and thread will be destroyed or sent back to connection pool managed by container.