Servlet interview questions

What is the Servlet?

A servlet is a Java programming language class that is used to extend the capabilities of servers that host applications accessed by means of a request- response programming model.

What are the uses of Servlet?

Typical uses for HTTP Servlets include:

Processing and/or storing data submitted by an HTML form.

Providing dynamic content, e.g. returning the results of a database query to the client.

A Servlet can handle multiple request concurrently and be used to develop high performance system

Managing state information on top of the stateless HTTP, e.g. for an online shopping cart system which manages shopping carts for many concurrent customers and maps every request to the right customer.

How the servlet is loaded?

A servlet can be loaded when:

First request is made.

Server starts up (auto-load).

There is only a single instance which answers all requests concurrently. This saves memory and allows a Servlet to easily manage persistent data.

Administrator manually loads.

What is Servlet interface?

The central abstraction in the Servlet API is the Servlet interface. All servlets implement this interface, either directly or , more commonly by extending a class that implements it.

Note: Most Servlets, however, extend one of the standard implementations of that interface, namely javax.servlet.GenericServlet andjavax.servlet.http.HttpServlet.

What is difference between forward() method of RequestDispatcher and sendRedirect() method ?

forward() method	sendRedirect() method
1) forward() sends the same request to another resource.	1) sendRedirect() method sends new request always because it uses the URL bar of the browser.
2) forward() method works at server side.	2) sendRedirect() method works at client side.
3) forward() method works within the server only.	3) sendRedirect() method works within and outside the server.

 

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

doGet()	doPost()
In doGet() the parameters are appended to the URL and sent along with header information	In doPost(), on the other hand will (typically) send the information through a socket back to the webserver and it won't show up in the URL bar.
The amount of information you can send back using a GET is restricted as URLs can only be 1024 characters.	You can send much more information to the server this way - and it's not restricted to textual data either. It is possible to send files and even binary data such as serialized Java objects!
doGet() is a request for information; it does not (or should not) change anything on the server. (doGet() should be idempotent)	doPost() provides information (such as placing an order for merchandise) that the server is expected to remember
Parameters are not encrypted	Parameters are encrypted
doGet() is faster if we set the response content length since the same connection is used. Thus increasing the performance	doPost() is generally used to update or post some information to the server.doPost is slower compared to doGet since doPost does not write the content length
doGet() should be idempotent. i.e. doget should be able to be repeated safely many times	This method does not need to be idempotent. Operations requested through POST can have side effects for which the user can be held accountable.
doGet() should be safe without any side effects for which user is held responsible	This method does not need to be either safe
It allows bookmarks.	It disallows bookmarks.

What is the difference between PrintWriter and ServletOuputStream?

PrintWriter is a character-stream class where as ServletOutputStream is a byte-stream class. The PrintWriter class can be used to write only character-based information where as ServletOutputStream class can be used to write primitive values as well as character-based information.

What is the difference between GenericServlet and HttpServlet?

GenericServlet	HttpServlet
The GenericServlet is an abstract class that is extended by HttpServlet to provide HTTP protocol-specific methods.	An abstract class that simplifies writing HTTP servlets. It extends the GenericServlet base class and provides an framework for handling the HTTP protocol.
The GenericServlet does not include protocol-specific methods for handling request parameters, cookies, sessions and setting response headers.	The HttpServlet subclass passes generic service method requests to the relevant doGet() or doPost() method.
GenericServlet is not specific to any protocol.	HttpServlet only supports HTTP and HTTPS protocalls.