JSP - Life Cycle
The key to
understanding the low-level functionality of JSP is to understand the simple
life cycle they follow. A JSP life cycle can be defined as the entire process
from its creation till the destruction which is similar to a servlet life cycle
with an additional step which is required to compile a JSP into servlet. The
following are the paths followed by a JSP
Compilation
Initialization
Execution
Cleanup
The four major phases of JSP life cycle
are very similar to Servlet Life Cycle and they are as follows:
jsp life cycle
JSP Compilation:
When a browser asks
for a JSP, the JSP engine first checks to see whether it needs to compile the
page. If the page has never been compiled, or if the JSP has been modified
since it was last compiled, the JSP engine compiles the page. The compilation
process involves three steps:
Parsing
the JSP.
Turning
the JSP into a servlet.
Compiling
the servlet.
JSP Initialization:
When a container loads a JSP it invokes
the jspInit() method before servicing any requests. If you need to perform
JSP-specific initialization, override the jspInit() method:
public void
jspInit()
{
// Initialization code...
}
Typically
initialization is performed only once and as with the servlet init method, you
generally initialize database connections, open files, and create lookup tables
in the jspInit method.
JSP Execution:
This phase of the JSP life cycle
represents all interactions with requests until the JSP is destroyed.
Whenever a
browser requests a JSP and the page has been loaded and initialized, the JSP
engine invokes the _jspService() method in the JSP.
The
_jspService() method takes an HttpServletRequest and an HttpServletResponse
as its parameters as follows:
void
_jspService(HttpServletRequest request, HttpServletResponse response)
{
// Service handling code...
}
The
_jspService() method of a JSP is invoked once per a request and is responsible
for generating the response for that request and this method is also
responsible for generating responses to all seven of the HTTP methods ie. GET,
POST, DELETE etc.
JSP Cleanup:
The destruction phase of the JSP life
cycle represents when a JSP is being removed from use by a container. The jspDestroy()
method is the JSP equivalent of the destroy method for servlets. Override
jspDestroy when you need to perform any cleanup, such as releasing database
connections or closing open files. The jspDestroy() method has the following
form:
public void jspDestroy()
{
// Your cleanup code goes here.
}
