JSP Servlet J2EE Questions 2

6: What are implicit objects? List them?
A: Certain objects that are available for the use in JSP documents without

being declared first. These objects are parsed by the JSP engine and inserted into

the generated servlet. The implicit objects re listed below
• request
• response
• pageContext
• session
• application
• out
• config
• page
• exception

7: Difference between forward and sendRedirect?
A: When you invoke a forward request, the request is sent to another resource
on the server, without the client being informed that a different resource is going
to process the request. This process occurs completly with in the web container.
When a sendRedirtect method is invoked, it causes the web container to return to
the browser indicating that a new URL should be requested. Because the browser
issues a completly new request any object that are stored as request attributes
before the redirect occurs will be lost. This extra round trip a redirect is slower
than forward.

8: What are the different scope valiues for the <jsp:useBean>?
A: The different scope values for <jsp:useBean> are
1. page
2. request
3.session
4.application

9: Explain the life-cycle mehtods in JSP?
A: THe generated servlet class for a JSP page implements the HttpJspPage
interface of the javax.servlet.jsp package. Hte HttpJspPage interface extends the
JspPage interface which inturn extends the Servlet interface of the javax.servlet
package. the generated servlet class thus implements all the methods of the these
three interfaces. The JspPage interface declares only two mehtods - jspInit() and
jspDestroy() that must be implemented by all JSP pages regardless of the
client-server protocol. However the JSP specification has provided the HttpJspPage
interfaec specifically for the JSp pages serving HTTP requests. This interface
declares one method _jspService().
The jspInit()- The container calls the jspInit() to initialize te servlet
instance.It is called before any other method, and is called only once for a
servlet instance.
The _jspservice()- The container calls the _jspservice() for each request, passing
it the request and the response objects.
The jspDestroy()- The container calls this when it decides take the instance out of
service. It is the last method called n the servlet instance.

10: How do I prevent the output of my JSP or Servlet pages from being cached by
the browser?
A: You will need to set the appropriate HTTP header attributes to prevent the
dynamic content output by the JSP page from being cached by the browser. Just
execute the following scriptlet at the beginning of your JSP pages to prevent them
from being cached at the browser. You need both the statements to take care of some
of the older browser versions.
<%
response.setHeader("Cache-Control","no-store"); //HTTP 1.1
response.setHeader("Pragma\","no-cache"); //HTTP 1.0
response.setDateHeader ("Expires", 0); //prevents caching at the proxy server
%>