JSP Servlet J2EE Questions 13

61. What is session tracking and how do you track a user session in servlets?
Session tracking is a mechanism that servlets use to maintain state about a series
requests from the same user across some period of time. The methods used for
session tracking are: a) User Authentication - occurs when a web server restricts
access to some of its resources to only those clients that log in using a
recognized username and password. b) Hidden form fields - fields are added to an
HTML form that are not displayed in the client’s browser. When the form containing
the fields is submitted, the fields are sent back to the server. c) URL rewriting -
every URL that the user clicks on is dynamically modified or rewritten to include
extra information. The extra information can be in the form of extra path
information, added parameters or some custom, server-specific URL change. d)
Cookies - a bit of information that is sent by a web server to a browser and which
can later be read back from that browser. e) HttpSession- places a limit on the
number of sessions that can exist in memory. This limit is set in the session.
maxresidents property.

62. What is Server-Side Includes (SSI)?- Server-Side Includes allows embedding
servlets within HTML pages using a special servlet tag. In many servlets that
support servlets, a page can be processed by the server to include output from
servlets at certain points inside the HTML page. This is accomplished using a
special internal SSINCLUDE, which processes the servlet tags. SSINCLUDE servlet
will be invoked whenever a file with an. shtml extension is requested. So HTML
files that include server-side includes must be stored with an . shtml extension.

63. What are cookies and how will you use them?- Cookies are a mechanism that a
servlet uses to have a client hold a small amount of state-information associated
with the user. a) Create a cookie with the Cookie constructor: public Cookie(String
name, String value) b) A servlet can send a cookie to the client by passing a
Cookie object to the addCookie() method of HttpServletResponse: public void
HttpServletResponse. addCookie(Cookie cookie) c) A servlet retrieves cookies by
calling the getCookies() method of HttpServletRequest: public Cookie[ ]
HttpServletRequest. getCookie().

64. Is it possible to communicate from an applet to servlet and how many ways
and how?- Yes, there are three ways to communicate from an applet to servlet and
they are: a) HTTP Communication(Text-based and object-based) b) Socket
Communication c) RMI Communication

65. What is connection pooling?- With servlets, opening a database connection
is a major bottleneck because we are creating and tearing down a new connection for
every page request and the time taken to create connection will be more. Creating a
connection pool is an ideal approach for a complicated servlet. With a connection
pool, we can duplicate only the resources we need to duplicate rather than the
entire servlet. A connection pool can also intelligently manage the size of the
pool and make sure each connection remains valid. A number of connection pool
packages are currently available. Some like DbConnectionBroker are freely available
from Java Exchange Works by creating an object that dispenses connections and
connection Ids on request. The ConnectionPool class maintains a Hastable, using
Connection objects as keys and Boolean values as stored values. The Boolean value
indicates whether a connection is in use or not. A program calls getConnection()
method of the ConnectionPool for getting Connection object it can use; it calls
returnConnection() to give the connection back to the pool.