9. Servlet Interview Questions

 

|| Servlet Interview Questions ||

1. What is servlet?

Servlet is a server side programming language which is used for generating dynamic web pages. It generates web-page as a response of the request received from client(browser).

2. Static webpage vs Dynamic webpage?

The webpages which are same for all the users are static webpages and the webpages that are dynamically generated based on the user’s request (that may be different for each user depending on the request) are known as dynamic webpages. Servlet is mainly used for dynamic webpages.

3. Life cycle of a servlet?

Following the the stages of servlet life cycle:

1) Loading of Servlet class: The servlet container finds the servlet class mentioned in web.xml file and loads it.

2) Servlet instantiation: The object of servlet class gets created in this phase.

3) Initialization: Servlet initialization by calling init() method.

4) Servicing the request: In this phase the servlet service the client request by calling the service() method.

5) Destroy: Last phase of servlet life cycle. The destroy() method free up the servlet instance so that it can be garbage collected.

4. Why we use Servlets?

1) To process the input data submitted by user from the screen.

2) Generate and return the dynamic response to the user based on the request.

3) Ideal programming language for interacting with database based on the user’s request.

4) A servlet can handle multiple request simultaneously which makes them a perfect choice for the high performing applications.

5. Why Servlet is better than CGI(Common Gateway Interface) ?

1) Servlet responses faster than CGI because it uses the multithreading concept to service each request. CGI performance is not that good as it creates a new object for each request while servlet allots a new thread for each request.

2) Learning and implementing servlet is quite easier compared to CGI.

3) Memory consumption is low in servlet compared to CGI.

6. When Servlet is loaded?

1) When servlet container receives the first request from client(browser).

2) Admin of the application manually loads the servlet.

3) When the webserver(in which the servlet is deployed) gets started.

7. What is Servlet interface and what’s the use of it?

Servlet interface is an API for servlets. Every Servlet should either implement the servlet interface or extends the class which already implements the interface. javax.servlet.GenericServlet and javax.servlet.http.HttpServlet are the Servlet classes that implements Servlet interface, hence every servlet should either implement Servlet interface directly or by extending any of these classes.

8. What is ServletContext?

Each web application has a common ServletContext. All the servlets in the web application can access the ServletContext. It has the web-application information & resources which are common and accessible to all the servlets present in the web application.

9. ServletConfig vs ServletContext?

Following are the two main differences between ServletConfig and ServletContext:

1) ServletConfig is used for passing the configuration information to the Servlet while ServletContext provides set of methods which a Servlet class can use to communicate with Servlet container.

2) Each Servlet has a separate ServletConfig object while ServletContext is common for all the servlets in the web application.

3) Parameters of ServletConfig are defined under <init-param> tags in web.xml file. Parameters of ServletContext are defined under <context-param> tags in web.xml.

10. Difference between GenericServlet and HTTPServlet?

1) GenericServlet is an abstract class which implements Servlet interface while HTTPServlet abstract class extends the GenericServlet class. In short: GenericServlet class is a parent class for HTTPServlet.

2) GenericServlet does not support any protocol. HTTPSeervlet support HTTP and HTTPS protocol.

3) GenericServlet cannot handle cookies and session while HTTPServlet can handle them.

11. Difference between forward() and sendRedirect()?

1) In forward() the same request is forwarded to the another resource. In sendRedirect() new request is send to the redirected resource.

2) forward() is taken care by the Servlet container while sendRedirect() is handled by the browser.

3) In forward() the URL(uniform resource locator) remains same on web browser. In sendRedirect() the URL changes in the web browser address bar.

4) forward() is faster compared to sendRedirect().

12. doGet() Vs doPost() methods?

1) In doGet(), the parameters are visible in the address bar, they get appended to the URL. In doPost() parameters are not visible in the address bar.

2) You can maximum transfer 1024 characters through GET request. doPost() doesn’t have any limitations.

3) doGet() is not good for sensitive data as the parameters do not get encrypted. In doPost() the parameters are encrypted hence it is more secure compared to doGet().

4) Method doGet() allow you to bookmark the resource. doPost() doesn’t allow bookmarks.

5) doGet() is faster compared to the doPost() method.

13. What are the main functions of Servlet container?

1) Servlet life cycle management

2) Maintains the interaction between servlet and webserver.

3) Providing multithreading support for processing more than one request simultaneously.

4) Managing of deployment descriptor web.xml file.

14. What is Servlet lazy loading and how it can be avoided?

The Servlet container does not initialize the Servlet on server startup by default. It only initializes a servlet when the it receives the request from the client. This is called lazy loading of Servlet.

By specifying <load-on-startup> element for a Servlet we can avoid lazy loading. The servlet files specified in <load-on-startup> are loaded as soon as the web sever starts.

15. When the Servlet is unloaded?

1) Admin manually unloads the servlet.

2) Web server shut down.

16. How Servlet maintains session using cookies?

Cookie is a small piece of information, which is sent by a servlet to the Web browser. Cookies gets stored in the browser and returned back to the server when needed. A cookie has a name, a single value, and few other attributes.

17. Why we use filters in Servlet?

We use filters for:

1) Security checks

2) Modifying the request or response

3) Data compression

4) Logging and auditing

5) Response compression

18. What all protocols are supported by HTTPServlet?

HTTP and HTTPS protocols.

19. What are the new features added to Servlet 3?

1) Servlet Annotations

2) Web Fragments

3) Web components addition dynamically

4) Asynchronous Processing