J2EE: SERVLET: Servlet Life Cycle

  Life cycle of a servlet starts when its first load in the memory space in web server and ends when unloaded from the server memory. we can divide this in 3 steps.

STEP 1: INITIALIZATION:

• Server loads the servlet class.
• Creates an instance for the servlet class.
• Server initializes the instance by calling init() method. 

STEP 2: SERVICE:

• Server creates a request & a respond object based on the client's request.
• Invokes the service() method of the servlet, passing the request respond object.
• service() method process the request and use the respond object to create the client respond.
• service() method can invoke can also invoke other methods like doGet(), doPost(), doDelete(), doOptions(), doPut() and doTrace().

STEP 3: DESTROY:

• Server calls the destroy() method to relinquish any resources such as file handles that are allocated to that servlet. destroy() method is invoked once in a servlet's life time.
• Then the server unload the servlet and its objects, and it's memory can be garbage collected.

                   *Unavailable exception thrown       *Initialization failed