HTTP server

25 Best Servlet Interview Questions and Answers - Java J2EE

What Is Servlet?
Java Servlet is a server side programming which used to generating dynamic web pages and it also generates web page as a response of the request received from browsers.

Java Servlet is a class which responds to a particular type of network request - HTTP request.
All servlets must implement the javax.servlet.Servlet interface which defines servlet life-cycle methods.

Java Servlet are programs that run on a Web server and it work in the middle layer between a request coming from the Web browsers and databases on the HTTP server.

How Many Objects of a Servlet is created?
Only one object at the time of first request by servlet or web container.

Web container manages the life cycle of a servlet and helps to map the URL to a specific servlet and web container creates the object of a servlet.

Do we override service () method?
No!, we do not override the service() method.

What's New Features Added to Servlet 3?
The main aims to offer Web developers greater simplicity and ease of development while adhering to Web 2.0 principles.

1.      Servlet Annotations
2.      Web Fragments
3.      Web components addition dynamically
4.      Asynchronous Processing
5.      Servlet 3 supports annotation to eliminate web.xml
1.      @WebServlet
2.      @WebServletContextListener
3.      @ServletFilter
4.      @InitParam

What Is Difference Between Cookies and HttpSession?
The Cookie works at client side whereas HttpSession works at server side.

How do I get the server info in Servlet?
To get server info using the getServletContext().getServerInfo()

How to get the client’s IP address in Servlets?
To get client IP address using request.getRemoteAddr()

What Are Different Ways for Servlet Authentication?
1.      HTTP Basic Authentication
2.      HTTP Digest Authentication
3.      HTTPS Authentication
4.      Form Based Login

When Servlet Object Is Created?
At the time of first request, the servlet object created.

What Are packages that work with Servlet?
There are two packages which work with Servlet: One is - Javax.servlet and second one is - Javax.servlet.http

A servlet life-cycle can be defined as the entire process from its creation till the destruction. The Stages of the Servlet Life Cycle:

1.      Servlet is loaded
2.      Servlet is instantiated
3.      Servlet is initialized
4.      Service the request
5.      Servlet is destroyed
Source - (http://www.javachain.com/servlet-life-cycle/)

How Is a Servlet Implemented in code?
Simply extending the Httpservlet or generic servlet class

What Is the use of Generic Servlet?
The Generic Servlet can handle all type of requests.

Is Servlet Synchronized?
No!, the servlets are not synchronized. If you want, we must implement SingleThreadInterface

Is it possible to have a Constructor inside the Servlet?
Yes!, it is possible to define a constructor inside a servlet, but it can be called only by Servlet container and not explicitly.

What Are the Servlet Life Cycle Methods?
There are three life cycle methods of a Servlet:
1.      The init() method - The init method is used to initialize the servlet.
2.      The service() method - The service method is used to service the request.
3.      The destroy() method - The destroy method invoked only once when servlet is unloaded.

Finally, servlet is garbage collected by the garbage collector of the JVM.

The service() method checks the HTTP request type - GET, POST, PUT, DELETE and calls doGet, doPost, doPut, doDelete.

Example:
The prototype for the init() method:

Public void init(ServletConfig serObj)throws ServletException{ }

Example:
The prototype for this method:

Public void service(ServletRequest req, ServletResponse resp) throws ServletException, IOException { }

Example:
The prototype for this method:
Public void destroy() {}

How Many times each Life Cycle method of a Servlet called?
The init() method is called only once during the life cycle of servlet. Each time the server receives a request for a servlet, the server spawns a new thread and calls service() method.

Who Is Responsible to create the Object of Servlet?
The web container and servlet container is responsible to create the object.

What Is Scope Object and How Many Types?
The Scope objects is use to share the information among web components with the help of setattribute() and getattribute().

The Types of Scope Objects:
1.      Web Context
2.      Session
3.      Request
4.      Page

What All Protocols Are Supported by HTTPServlet?
HTTP protocol
HTTPS protocol

What Kinds of HTTP Requests?
1.      Get() method
2.      Post() method
3.      Head() method
4.      Options() method
5.      Put() method
6.      Trace() method
7.      Delete() method

How To Invalidate a Session in Servlet?
To invalidate session by calling session.invalidate() method.

What Are the Different Types of Session Tracking Mechanism supported by Servlets?
1.      URL rewriting
2.      Hidden Form Fields
3.      Cookies
4.      Secure Socket Layer (SSL) Sessions

What Is HTTPServletRequest class?
What Is HTTPServletResponse class?
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