Some more Java Interview Questions Part-4

What is the servlet?
Servlet is a script, which resides and executes on server side, to create dynamic HTML. In servlet programming we will use java language. A servlet can handle multiple requests concurrently

What is the architechture of servlet package?
Servlet Interface is the central abstraction. All servlets implements this Servlet
Interface either direclty or indirectly
( may implement or extend Servlet Interfaces sub classes or sub interfaces)

Servlet

Generic Servlet

HttpServlet ( Class ) -- we will extend this class to handle GET / PUT HTTP requests

MyServlet

What is the difference between HttpServlet and GenericServlet?
A GenericServlet has a service() method to handle requests.
HttpServlet extends GenericServlet added new methods
doGet()
doPost()
doHead()
doPut()
doOptions()
doDelete()
doTrace() methods
Both these classes are abstract.

What's the difference between servlets and applets?
Servlets executes on Servers. Applets executes on browser. Unlike applets, however, servlets have no graphical user interface.

What are the uses of Servlets?
A servlet can handle multiple requests concurrently, and can synchronize requests. Servlets can forward requests to other servers and servlets. Thus servlets can be used to balance load among several servers.


When doGET() method will going to execute?
When we specified method='GET' in HTML
Example : < name="'SSS'" method="'GET'">

When doPOST() method will going to execute?
When we specified method='POST' in HTML
< name="'SSS'" method="'POST'">


What is the difference between Difference between doGet() and doPost()?
GET Method : Using get method we can able to pass 2K data from HTML
All data we are passing to Server will be displayed in URL (request string).

POST Method : In this method we does not have any size limitation.
All data passed to server will be hidden, User cannot able to see this info
on the browser.

Which code line must be set before any of the lines that use the PrintWriter?
setContentType() method must be set.

Which protocol will be used by browser and servlet to communicate ?
HTTP


In how many ways we can track the sessions?
Method 1) By URL rewriting
Method 2) Using Session object

Getting Session form HttpServletRequest object
HttpSession session = request.getSession(true);

Get a Value from the session
session.getValue(session.getId());

Adding values to session
cart = new Cart();

session.putValue(session.getId(), cart);
At the end of the session, we can inactivate the session by using the following command
session.invalidate();

Method 3) Using cookies
Method 4) Using hidden fields