Java Reference
In-Depth Information
As we can see, the
doPost()
and
doGet()
methods for our servlet simply invoke
the generated
processRequest()
method, passing along the
request
and
response
parameters. If we wish our servlet to handle only
POST
request, we should delete
the generated
doGet()
method; similarly, if we wish the servlet to handle only
GET
request, the
doPost()
method should be deleted.
We need our servlet to process data entered by the user in the application's input
page, then invoke the output page, which will be modified to obtain its data from an
attribute in the HTTP request.
In our example we modified the
processRequest()
method of our servlet so that it
creates an instance of a JavaBean called
SurveyData
and populates it with values
from the request parameters.
SurveyData
is a very simple JavaBean with two private properties and
corresponding getters and setters. Since it is so simple, it is not shown; it
is part of this topic's code download. This bean's role is to be the model in
our MVC architecture.
The instance of
SurveyData
is then stored as a request attribute by invoking the
setAttribute()
method in the request object. Request attributes are visible as long
as no new HTTP request is generated from the application. We can navigate to other
pages by forwarding the request and its attributes will be preserved. Redirecting
the HTTP response, clicking on a link, submitting a page or entering a URL directly
in the browser's location field are all actions that generate a new request, causing
previous request attributes to be lost.
A different way of transferring control to another URL is by using the
sendResponseRedirect()
method of
HttpServletResponse
. This
method takes a single
String
argument containing the URL we wish to
redirect to. This method creates a new request, therefore any pre-existing
request attributes and parameters are lost. The URL used as a parameter
can be a page on any server, where forwarding the request is limited to
pages or resources in the same server as the one where the servlet or JSP
doing the forwarding is deployed.
