25-05-2012, 11:41 AM
Servlet Interview Questions
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1. What is a Servlet?
Java Servlets are server side components that provides a powerful mechanism for developing
server side of web application. Earlier CGI was developed to provide server side capabilities to the web
applications. Although CGI played a major role in the explosion of the Internet, its performance,
scalability and reusability issues make it less than optimal solutions. Java Servlets changes all that.
Built from ground up using Sun's write once run anywhere technology java servlets provide excellent
framework for server side processing.
2. What are the types of Servlet?
There are two types of servlets, GenericServlet and HttpServlet. GenericServlet defines the
generic or protocol independent servlet. HttpServlet is subclass of GenericServlet and provides some
http specific functionality linke doGet and doPost methods.
3. What are the differences between HttpServlet and Generic Servlets?
HttpServlet Provides an abstract class to be subclassed to create an HTTP servlet suitable for a
Web site. A subclass of HttpServlet must override at least one method, usually one of these:
· doGet, if the servlet supports HTTP GET requests
· doPost, for HTTP POST requests
· doPut, for HTTP PUT requests
· doDelete, for HTTP DELETE requests
· init and destroy, to manage resources that are held for the life of the servlet
· getServletInfo, which the servlet uses to provide information about itself
There's almost no reason to override the service method. Service handles standard HTTP requests by
dispatching them to the handler methods for each HTTP request type (the doXXX methods listed
above). Likewise, there's almost no reason to override the doOptions and doTrace methods.
GenericServlet defines a generic, protocol-independent servlet. To write an HTTP servlet for use on
the Web, extend HttpServlet instead.
GenericServlet implements the Servlet and ServletConfig interfaces. GenericServlet may be directly
extended by a servlet, although it's more common to extend a protocol-specific subclass such as
HttpServlet.
GenericServlet makes writing servlets easier. It provides simple versions of the lifecycle methods init
and destroy and of the methods in theServletConfig interface. GenericServlet also implements the log
method, declared in the ServletContext interface.
To write a generic servlet, you need only override the abstract service method.
4. Differentiate between Servlet and Applet.
Servlets are server side components that executes on the server whereas applets are client side
components and executes on the web browser. Applets have GUI interface but there is not GUI
interface in case of Servlets.
5. Differentiate between doGet and doPost method?
doGet is used when there is are requirement of sending data appended to a query string in the
URL. The doGet models the GET method of Http and it is used to retrieve the info on the client from
some server as a request to it. The doGet cannot be used to send too much info appended as a query
stream. GET puts the form values into the URL string. GET is limited to about 256 characters (usually
a browser limitation) and creates really ugly URLs.
POST allows you to have extremely dense forms and pass that to the server without clutter or
limitation in size. e.g. you obviously can't send a file from the client to the server via GET. POST has
no limit on the amount of data you can send and because the data does not show up on the URL you
can send passwords. But this does not mean that POST is truly secure. For real security you have to
look into encryption which is an entirely different topic