Filters are defined in the deployment descriptor file web.xml and then mapped to either servlet or
JSP names or URL patterns in your application's deployment descriptor.
When the JSP container starts up your web application, it creates an instance of each filter that you
have declared in the deployment descriptor. The filters execute in the order that they are declared
in the deployment descriptor.
62.What are cookies?
Cookies are text files stored on the client computer and they are kept for various information
tracking purpose.
63.How cookies work?
Cookies are usually set in an HTTP header althoughJavaScriptcanalsosetacookiedirectlyonabrowser.If the
browser is configured to store cookies, it will then keep this information until the expiry date. If the
user points the browser at any page that matches the path and domain of the cookie, it will resend
the cookie to the server.
64.How do you set cookies in the JSP?
Creating a Cookie object: You call the Cookie constructor with a cookie name and a cookie
value, both of which are strings.
Setting the maximum age: You use setMaxAge to specify how long inseconds the cookie
should be valid.
Sending the Cookie into the HTTP response headers: You use response.addCookie to
add cookies in the HTTP response header
65.How to read cookies with JSP?
To read cookies, you need to create an array of javax.servlet.http.Cookie objects by calling the
getCookies method of HttpServletRequest. Then cycle through the array, and use getName and
getValue methods to access each cookie and associated value.
66.How to delete cookies with JSP?
To delete cookies is very simple. If you want to delete a cookie then you simply need to follow up
following three steps:
Read an already existing cookie and store it in Cookie object.
Set cookie age as zero using setMaxAge method to delete an existing cookie.
Add this cookie back into response header.
67.How is Session Management done in JSP?
Session management can be achieved by the use of:
Cookies: A webserver can assign a unique session ID as a cookie to each web client and for
subsequent requests from the client they can be recognized using the received cookie.
Hidden Form Fields: A web server can send a hidden HTML form field along with a unique
session ID as follows:
This implies that when the form is submitted, the specified name and value will be getting
included in GET or POST method.
URL Rewriting: In URL rewriting some extra information is added on the end of each URL
that identifies the session. This URL rewriting can be useful where a cookie is disabled.
The session Object: JSP makes use of servlet provided HttpSession Interface which
provides a way to identify a user across more than one page request or visit to a Web site
and to store information about that user.
68.How can you delete a session data?
When you are done with a user's session data, you have several options:
Remove a particular attribute: You can call public void removeAttributeStringname method
to delete the value associated with a particular key.
Delete the whole session: You can call public void invalidate method to discard an entire
session.
Setting Session timeout: You can call public void setMaxInactiveIntervalintinterval method
to set the timeout for a session individually.
Log the user out: The servers that support servlets 2.4, you can call logout to log the
client out of the Web server and invalidate all sessions belonging to all the users.
web.xml Configuration: If you are using Tomcat, apart from the above mentioned
methods, you can configure session time out in web.xml file as follows.
69.How can you upload a file using JSP?
To upload a single file you should use a single (input .../) tag with attribute type="file".To allow
multiple files uploading, include more than one input tags with different values for the name
attribute.
70.Where will be the uploaded files stored?
You can hard code this in your program or this directory name could also be added using an
external configuration such as a context-param element in web.xml.
71.What is JSP page redirection?
Page redirection is generally used when a document moves to a new location and we need to send
the client to this new location or may be because of load balancing, or for simple randomization.
72.What is the difference between (jsp:forward page = ... ) and response.sendRedirecturl?
The element forwards the request object containing the client request information
from one JSP file to another file. The target file can be an HTML file, another JSP file, or a servlet, as
long as it is in the same application context as the forwarding JSP file.
sendRedirect sends HTTP temporary redirect response to the browser, and browser creates a new
request to go the redirected page.
73.What is a hit count for a web page?
A hit counter tells you about the number of visits on a particular page of your web site.
74.How do you impement hit counter in JSP?
To implement a hit counter you can make use of Application Implicit object and associated
methods getAttribute and setAttribute.
This object is a representation of the JSP page through its entire lifecycle. This object is created
when the JSP page is initialized and will be removed when the JSP page is removed by the
jspDestroy method.
75.How can you implement hit counter to avoid loss of count data with each restart of thh application?
You can follow the below steps:
Define a database table with a single count, let us say hitcount. Assign a zero value to it.
With every hit, read the table to get the value of hitcount.
Increase the value of hitcount by one and update the table with new value.
Display new value of hitcount as total page hit counts.
If you want to count hits for all the pages, implement above logic for all the pages.
76.What is auto refresh feature?
Consider a webpage which is displaying live game score or stock market status or currency
exchange ration. For all such type of pages, you would need to refresh your web page regularly
using refresh or reload button with your browser.
JSP makes this job easy by providing you a mechanism where you can make a webpage in such a
way that it would refresh automatically after a given interval.
77.How do you implement the auto refresh in JSP?
The simplest way of refreshing a web page is using method setIntHeader of response object.
Following is the signature of this method: public void setIntHeader(String header, int headerValue)
This method sends back header "Refresh" to the browser along with an integer value which
indicates time interval in seconds.
78.What is JSTL?
The JavaServer Pages Standard Tag Library JSTL is a collection of useful JSP tags which
encapsulates core functionality common to many JSP applications.
JSTL has support for common, structural tasks such as iteration and conditionals, tags for
manipulating XML documents, internationalization tags, and SQL tags. It also provides a framework
for integrating existing custom tags with JSTL tags.
79.What the different types of JSTL tags are ?
Types of JSTL tags are:
Core Tags
Formatting tags
SQL tags
XML tags
JSTL Functions
80.What is the use of (c:set ) tag?
The (c:set ) tag is JSTL-friendly version of the setProperty action. The tag is helpful because it
evaluates an expression and uses the results to set a value of a JavaBean or a java.util.Map object.
