Lifecycle of a JSP page

A JSP page is not executed directly. In order for a JSP page to handle user requests, every JSP page is first translated to a Servlet and has to go through a few more phases before it could actually take user requests and respond appropriately. Let's discuss these phases in the life of every JSP page or also known as Lifecycle of a JSP page. These stages or phases are performed in the order in which they are mentioned below.

JSP Page Translation.

Compilation.

Loading and Initialization.

Handling Requests.

Destroy.

JSP Page Translation

Servlet

Java Virtual Machine(JVM)

JSP page translation process takes place in either of these two situations -

When a JSP page has to serve to a client's request for the first time, it is translated to a Servlet code.

When a JSP page is updated or changed and it has to redeployed by the Web Container.

Compilation

.class

Loading and Initialization

Loading the Servlet - The Servlet bytecode(.class) file is loaded by the Web Container.

Initializing the Servlet- Next, an instance of Servlet class is created when the Web Container calls the no-argument of Servlet class. This no-argument is added to the Servlet class code by the Web Container when the JSP page is translated to its equivalent Servlet code. This object of Servlet class is then initialized by the Web Container, in order for the Servlet class to handle the user requests in the next phase.

Handling Requests

Creating the ServletRequest and ServletResponse instances - Based on whether the client is sending requests using the HTTP protocol or a NON-HTTP protocol, Web Container creates the instances of ServletRequest and ServletResponse or it creates instances of HTTPServletRequest and HTTPServletResponse.

Calling the service() method - Next, the Web Container calls the service() method of JSP, which eventually calls the _jspService() method present in the translated Servlet class and the appropriate request and response objects are passed to this method, in order to handle client's request and respond appropriately.

Destroy

It allows all the current threads to complete their execution of the service() method on the Servlet object.

After all the threads have successfully completed their execution of service() method, the Web Container calls the destoy() method on the Servlet instance, to indicate to a Servlet that it is being taken out of service.