Life Cycle of Servlet

Three Life Cycle Methods of Servlet:

1. init
2. service
3. destroy

init Method:

•  The servlet is initialized by calling the init () method.
•  The init method is designed to be called only once.
• It is called when the servlet is first created, and not called again for each user request.
• When a user invokes a servlet, a single instance of each servlet gets created, with each user request resulting in a new thread that is handed off to doGet or doPost as appropriate.

            Signature of the init() method:
                   public void init() throws ServletException {
                          // Initialization code...
                   }

service Method:

•  The service() method is the main method to perform the actual task.
•  The servlet container (i.e. web server) calls the service() method to handle requests coming from the client( browsers) and to write the formatted response back to the client.
•  Each time the server receives a request for a servlet, the server create a new thread and calls service.
• The service() method checks the HTTP request type (GET, POST, etc.) and calls doGet, doPost etc. methods as appropriate.

              Signature of the service() method:
                   public void service(ServletRequest request, ServletResponse response)
                         throws ServlertException,IOException{
                       
                    }

• So you have nothing to do with service() method but you override either doGet() or doPost() depending on what type of request you receive from the client.
• The doGet() and doPost() are most frequently used methods with in each service request.

destroy Method:

•  The destroy() method is called only once at the end of the life cycle of a servlet.
•  This method gives your servlet a chance to close database connections, halt background threads, write cookie lists or hit counts to disk, and perform other such cleanup activities.
•  After the destroy() method is called, the servlet object is marked for garbage collection.
• servlet is garbage collected by the garbage collector of the JVM.

               Signature of the destroy() method:
                     public void destroy() {
                           // Finalization code...
                     }