What is the difference between GenericServlet, HttpServlet and a Servlet?

Servlet

is an interface defining what a servlet must implement.

GenericServlet

is just that, a generic, protocol-independent servlet.

HttpServlet

is a servlet tied specifically to the HTTP protocol.

In general, you’d extend

HttpServlet

to implement an application’s web layer.

You might implement

Servlet

if you’re writing your own container or handling everything yourself. You might extend

GenericServlet

to handle a different protocol, but you might not.

javax.servlet.Servlet

is interface, it defines methods for all the implementations - that’s what interfaces usually do.

javax.servlet.GenericServlet

is protocol independent. It is abstract, so it is not to be directly instantiated. It is usable class to extend if you some day have to write servlet for protocol other than HTTP.

javax.servlet.http.HttpServlet

is abstract class to be extended if you want to communicate over HTTP protocol. Most likely you only have to care about this one.

Servlet

is a server-side web technology. As the name implies, it serves a client request and receives a response from the server. You have to implement

javax.Servlet

(Interface) to handle a servlet work.

javax.servlet.GenericServlet

Signature:

public abstract class GenericServlet extends java.lang.Object implements Servlet, ServletConfig, java.io.Serializable

GenericServlet

defines a generic, protocol-independent servlet.

GenericServlet

gives a blueprint and makes writing servlet easier.

GenericServlet provides simple versions of the life-cycle methods

init

and

destroy

and of the methods in the

ServletConfig

interface.

GenericServlet implements the log method, declared in the

ServletContext

interface.

To write a generic servlet, it is sufficient to override the abstract

service()

method.

javax.servlet.http.HttpServlet

Signature:

public abstract class HttpServlet extends GenericServlet implements java.io.Serializable

HttpServlet defines a HTTP protocol specific servlet.

HttpServlet gives a blueprint for Http servlet and makes writing them easier.

HttpServlet extends the GenericServlet and hence inherits the properties GenericServlet.

HttpServlet

is specific to the HTTP protocol and hence it supplies methods for the HTTP verbs:

doGet

,

doPost

, etc, and a version of the generic service method that takes HTTP-specific request and response objects. It is a special type of Servlet which is actually a pretty minimal interface.

GenericServlet

is the basic, protocol-neutral implementation of the Servlet interface. Often you’ll find similar basic implementations of interfaces in an API; in this case

GenericServlet

adds a bit of functionality to the Servlet API:

getServletName

,

getServletInfo

, and pass-through methods for the servlet

init

parameters.

HttpServlet

benefits from these additions by extending

GenericServlet

.

Generally everyone coding against this API is using

HttpServlet

for implementing HTTP web services, but one can also extend or use

GenericServlet

for implementing server/service functionality using a custom protocol, or another extant protocol, for example, FTP.

Servlet

:-

The

Servlets

runs as a thread in a web-container instead of in a seperate OS process.

Only one object is created first time when first request comes, other request share the same object.

Servlet

is platform independent.

Servlet

is fast.

GenericServlet:-

General for all protocol.

Implements Servlet Interface.

Use Service method.

HttpServlet:-

Only for HTTP Protocol.

Inherit GenericServlet class.

Use doPost, doGet method instead of service method.