JAVA Servlet Interview Questions and Answers

What is the difference between HttpServlet and GenericServlet?

A GenericServlet has a service() method aimed to handle requests.
HttpServlet extends GenericServlet and adds support for doGet(), doPost(), doHead() methods (HTTP 1.0) plus doPut(), doOptions(), doDelete(), doTrace() methods (HTTP 1.1). Both these classes are abstract.

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Explain the life cycle methods of a Servlet?

The javax.servlet.Servlet interface defines the three methods known as life-cycle method.
public void init(ServletConfig config) throws ServletException
public void service( ServletRequest req, ServletResponse res) throws ServletException, IOException
public void destroy()


First the servlet is constructed, then initialized wih the init() method. 
Any request from client are handled initially by the service() method before delegating to the doXxx() methods in the case of HttpServlet. 
The servlet is removed from service, destroyed with the destroy() method, then garbaged collected and finalized. 

What is the difference between the getRequestDispatcher(String path) method of javax.servlet.ServletRequest interface and javax.servlet.ServletContext interface?

The getRequestDispatcher(String path) method of javax.servlet.ServletRequest interface accepts parameter the path to the resource to be included or forwarded to, which can be relative to the request of the calling servlet. If the path begins with a "/" it is interpreted as relative to the current context root.

The getRequestDispatcher(String path) method of javax.servlet.ServletContext interface cannot accepts relative paths. All path must sart with a "/" and are interpreted as relative to curent context root.

Explain the directory structure of a web application?.

The directory structure of a web application consists of two parts. 
A private directory called WEB-INF
A public resource directory which contains public resource folder.
WEB-INF folder consists of 
1. web.xml
2. classes directory
3. lib directory

What are the common mechanisms used for session tracking?

Cookies
SSL sessions
URL- rewriting

Explain ServletContex?.
ServletContext interface is a window for a servlet to view it's environment. A servlet can use this interface to get information such as initialization parameters for the web application or servlet container's version. Every web application has one and only one ServletContext and is accessible to all active resource of that application.
What is preinitialization of a servlet?
A container doesnot initialize the servlets as soon as it starts up, it initializes a servlet when it receives a request for that servlet first time. This is called lazy loading. The servlet specification defines the element, which can be specified in the deployment descriptor to make the servlet container load and initialize the servlet as soon as it starts up. The process of loading a servlet before any request comes in is called preloading or preinitializing a servlet.

What is the difference between Difference between doGet() and doPost()?

A doGet() method is limited with 2k of data to be sent, and doPost() method doesn't have this limitation. A request string for doGet() looks like the following: 
http://www.abc.com/svt1?p1=v1&p2=v2&...&pN=vN
doPost() method call doesn't need a long text tail after a servlet name in a request. All parameters are stored in a request itself, not in a request string, and it's impossible to guess the data transmitted to a servlet only looking at a request string. 

What is the difference between ServletContext and ServletConfig?

ServletContext: Defines a set of methods that a servlet uses to communicate with its servlet container, for example, to get the MIME type of a file, dispatch requests, or write to a log file.The ServletContext object is contained within the ServletConfig object, which the Web server provides the servlet when the servlet is initialized. 

ServletConfig: The object created after a servlet is instantiated and its default constructor is read. It is created to pass initialization information to the servlet.

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Fractions

First we increased the denominator of a positive fraction by 3 and then decrease it by 5.The sum of the resulting fractions proves to be equal to 2/3. Find the denominator of the fraction if its numerator is 2?

Simplification

If we divide a two digit number by the sum of its digits we get 4 as a quotient and 3 as a remainder. Now if we divide that two digit number by the product of its digits we get 3 as a quotient and 5 as a remainder . Find the two digit number?

Fractions

The denominators of an irreducible fraction is greater than the numerator by 2.If we reduce the numerator of the reciprocal fraction by 3 and subtract the given fraction from the resulting one,we get 1/15.Find the given fraction?

Simplification

If we add the square of the digit in the tens place of the positive two digit number to the product of the digits of that number we get 52,and if we add the square of the digit in the unit's place to the same product of the digits we get 117.Find the two digit number?

The sum of squares of the digits constituting a positive two digit number is 13, If we subtract 9 from that number we shall get a number written by the same digits in the reverse order. Find the number?

The arithmetic mean of two numbers is smaller by 24 than the larger of the two numbers and the GM of the same numbers exceeds by 12 the smaller of the numbers. Find the numbers?

A number being successively divided by 3,5,8 leaves remainder 1,4,7 respectively. Find the respective remainders if the order of divisors are reversed?

The sum of all possible two digit numbers formed from three different one digit natural numbers when divided by the sum of the original three numbers is equal to?

HCF and LCM

Find the HCF and LCM of the polynomial x2-5x+6 and x2-7x+10?

Simplification

When we multiply a certain two digit number by the sum of its digits , 405 is achieved. If we multiply the number written in reverse order of the same digits by the sum of the digits, we get 486. Find the number?

Average

The sum of two numbers is 15 and their geometric mean is 20% lower than their arithmetic mean. Find the numbers?

Numbers

The difference of 1025-7 and 1024+x is divisible by 3. find x=?

A number when divided by the sum of 555 and 445 gives two times their difference as quotient and 30 as remainder . The number is?

The sum of three prime numbers is 100.If one of them exceeds another by 36 then one of the numbers is?

Find the number of zeros in the factorial of the number 18?

If a number is multiplied by 22 and the same number is added to it then we get a number that is half the square of that number. Find the number?

In doing a division of a question with zero remainder,a candidate took 12 as divisor instead of 21.The quotient obtained by him was 35. The correct quotient is?

Fractions

A number when divided by 342 gives a remainder 47.When the same number is divided by 19 what would be the remainder?

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