Servlets Interview Questions and Answers

Ques 1. What is the difference between an application server and a Web server?

Ques 2. What are advantages of servlets over CGI?

In CGI for every request there is a new process started which is quiet an overhead. In servlets JVM stays running and handles each request using a light weight thread. In CGI if there are 5000 request then 5000 CGI program is loaded in memory while in servlets there are 5000 thread and only one copy of the servlet class.

Ques 3. What are the two important APIs in Servlets?

Two important packages are required to build servlet "javax.servlet" and "javax.servlet.http". They form the core of Servlet API. Servlets are not part of core Java but are standard extensions provided by Tomcat.

Ques 4. Can you explain in detail "javax.servlet" package?

javax.servlet package has interfaces and classes which define a framework in which servlets can operate. Let's first make a walk through of all the interfaces and methods and its description.

Interfaces in javax.servlet :-
Servlet Interface: This interface has the init( ), service( ), and destroy( ) methods that are called by the server during the life cycle of a servlet. Following are the method in Servlet interface :-

void destroy( ):- Executed when servlet is unloaded from the web server memory.

ServletConfig getServletConfig() :- Returns back a ServletConfig object that contains initialization data.

String getServletInfo( ):- Returns a string describing the servlet.

init method :- Called for first time when the servlet is initialized by the web server.

void service() method :- Called to process a request from a client.

ServletConfig Interface:- This interface is implemented by the servlet container. Servlet can access any configuration data when its loaded. The methods declared by this interface are summarized here: Following are the methods in ServletConfig interface:-

ServletContext getServletContext():- Gives the servlet context.

String getInitParameter(String param):- Returns the value of the initialization parameter named param.

Enumeration getInitParameterNames():- Returns an enumeration of all initialization parameter names.
String getServletName():- Returns the name of the invoking servlet.

Ques 5. What's the use of ServletContext?

ServletContext Interface:  It gives information about the environment. It represents a Servlet's view of the Web Application.Using this interface servlet can access raw input streams to Web Application resources, virtual directory translation, a common mechanism for logging information, and an application scope for binding objects.