Jsp life cycle

 

• jsp engine controls the life cycle of jsp
• Jsp life cycle is described by three life cycle methods and six life cycle phases

Jsp life cycle methods :

• jspInit()
• _jspService()
• jspDestroy()

• Jspinit() method is invoked when JSP page is initialized.
• The _jspService() method corresponds to the body of the jsp page.
• This method is defined automatically by the JSp container and should never be defined y the JSP page author.

Jsp Life cycle Phases: 

• Translation phase
• Compilation phase
• Instantiation phase
• initialization phase
• Servicing phase
• Destruction phase

• Jsp engine calls jspInit() method only once during the initialization phase of a jsp.
• similarly during destruction phase jsp engine calls jspDestory() method only once
• For each client request Jsp container calls _jspService() method once.

Jsp Translation phase:

• When client request comes for a jsp for the first time , jsp engine makes a full read of the jsp verifies the syntactical corectness of the jsp elements and converts code into a servlet source code .
• The process of JSP engine translating jsp into servlet nothing but translation phase of JSP.
• Therefore , we say that Jsp development is another style of development  asking container to develop the servlet is nothing but JSP developement
• Container generated servlet class is also known as page implementation class.

Jsp Compilation phase:

• The process of jsp engine compiling the page implementation class is nothing but compilation phase of jsp.
• Jsp engine uses JASPER compiler to compile the container generated servlet class source code.
• In the life of the Jsp Translation and compilation happens only once unless jsp source code modified.

Jsp Instantiation phase:

• Container creating the instance of generated servelt class is nothing but instantialtion phase of jsp
• actually now we have a servelt object.
• Servlet engine loads user user defined servlet class file from secondary memory into
  primary memory dynamically
  
  class c= class.forName("name");
  c.newInstance();
• Servlet engine creates the instance of loaded servlet class.
• Servlet engine uses the following piece of code to load the servlet clas  dynamically to instantiate it.
  Class c= class.forName("Servlet class name");
  c.newInstance();

Initialization:

• Servlet engine creates servletConfig object
• Servlet engine calls the init() method on the servlet instance by supplying servletconfig object
  as argument.
• Once init method completely executed servlet is ready to serve the client request.

Servicing : 

• Servlet engine creates servlet request and servlet response object based on the web server
  provided client information.
• Servlet engine calls service method on the servlet instance by supplying two object reference as arguments
• Once service method is completely executed , client request is served and request-response cycle is complete.
• Within the service method request object is used to capture the user input
• Response object is used to build the dynamic page and hand over the same to the web server

Destruction:

• Destruction phase of servlet represents servlet being removed from use by container