Life-cycle of JSP

2.What is the life-cycle of JSP?

When a request is mapped to a JSP page for the first time, it translates the JSP page into a servlet class and compiles the class. It is this servlet that services the client requests.
A JSP page has seven phases in its lifecycle, as listed below in the sequence of occurrence:

1. Translation
2. Compilation
3. Loading the class
4. Instantiating the class
5. jspInit() invocation
6. _jspService() invocation
7. jspDestroy() invocation

3.What is the jspInit() method?

The jspInit() method of the javax.servlet.jsp.JspPage interface is similar to the init() method of servlets. This method is invoked by the container only once when a JSP page is initialized. It can be overridden by a page author to initialize resources such as database and network connections, and to allow a JSP page to read persistent configuration data.

4.What is the _jspService() method?

SThe _jspService() method of the javax.servlet.jsp.HttpJspPage interface is invoked every time a new request comes to a JSP page. This method takes the HttpServletRequest and HttpServletResponse objects as its arguments. A page author cannot override this method, as its implementation is provided by the container.

5.What is the jspDestroy() method?

The jspDestroy() method of the javax.servlet.jsp.JspPage interface is invoked by the container when a JSP page is about to be destroyed. This method is similar to the destroy() method of servlets. It can be overridden by a page author to perform any cleanup operation such as closing a database connection.

6.What JSP lifecycle methods can I override?

You cannot override the _jspService() method within a JSP page. You can however, override the jspInit() and jspDestroy() methods within a JSP page. jspInit() can be useful for allocating resources like database connections, network connections, and so forth for the JSP page. It is good programming practice to free any allocated resources within jspDestroy().

7.How can I override the jspInit() and jspDestroy() methods within a JSP page?

The jspInit() and jspDestroy() methods are each executed just once during the lifecycle of a JSP page and are typically declared as JSP declarations:

<%! 
 public void jspInit() {
  . . .
 }
%>
<%!  
 public void jspDestroy() {
  . . . 
 }
%>