Introduction to Java Servlet

1. Enterprise Java
Unit-1
Chapter-3
• Introduction to Java Servlet
• CGI and Servlet
• Servlet Life Cycle
• Java Servlet API and Interface
By
Prof. Sandeep Vishwakarma

2. What is a Servlet?
• Servlet is a technology which is used to create
a web application.
• Servlet is an API that provides many interfaces
and classes including documentation.
• Servlet is an interface that must be
implemented for creating any Servlet.
• Servlet is a class that extends the capabilities
of the servers and responds to the incoming
requests. It can respond to any requests.
• Servlet is a web component that is deployed on
the server to create a dynamic web page.

4. CGI (Common Gateway Interface)
CGI technology enables the web server to call an external
program and pass HTTP request information to the
external program to process the request. For each request,
it starts a new process.

5. Disadvantages of CGI
 If the number of clients increases, it
takes more time for sending the
response.
 For each request, it starts a process,
and the web server is limited to start
processes.
 It uses platform dependent language
e.g. C, C++, perl.

6. Advantages of Servlet

7. Advantages of Servlet over
CGI
 Better performance: because it creates a
thread for each request, not process.
 Portability: because it uses Java language.
 Robust: JVM manages Servlets, so we
don't need to worry about the memory
leak, garbage collection, etc.
 Secure: because it uses java language.

8. What is Java Servlet ?

9. What is Java Servlet ?

10. Servlet Services

11. Why use Servlets ?

12. Why use Servlets ?

13. Servlet Life Cycle

14. The lifecycle of a servlet is controlled by
the web container in which the servlet
has been deployed. When a request is
mapped to a servlet, the container
performs the following steps.
1. If an instance of the servlet does not
exist,
then the web container
a. Loads the servlet class.
b. Creates an instance of the servlet
class.
c. Initializes the servlet instance by

15. 2. Invokes the service method, passing
request and response objects. Service
methods are discussed in Writing Service
Methods.

17. Servlet Lifecycle Steps:
1) Load the Servlet Class
The classloader is responsible to load the
servlet class. The servlet class is loaded when
the first request for the servlet is received by
the web container.
2) Create Servlet instance
The web container creates the instance of a
servlet after loading the servlet class. The
servlet instance is created only once in the
servlet life cycle.

18. 3) Call the init method
The web container calls the init method only
once after creating the servlet instance. The init
method is used to initialize the servlet. It is the
life cycle method of the javax.servlet.Servlet
interface.
4) call the service method
The web container calls the service method
each time when request for the servlet is
received. If servlet is not initialized, it follows
the first three steps as described above then
calls the service method. If servlet is initialized,

19. 5) destroy method is invoked
The web container calls the destroy method
before removing the servlet instance from the
service. It gives the servlet an opportunity to
clean up any resource for example memory,
thread etc.

20. Servlet Interface
 Servlet interface is a collection of Empty
method signatures.
 A servlet must directly or indirectly
implement
Servlet Interface
This interface holds following functionalities.
 Initializing the Servlet
 Handling client request
 Destroying the Servlet

21. Methods Description
init() Is used for initializing the Servlet parameters
provided by the ServletConfig object.
Is called only once when the Servlet is first
loaded. It is commonly used to initialize
resources to be used by a Servlet when
requests are received.
service(
)
Is the actual heart of the HTTP Request-
Response model. It is called to handle a single
client request. A Servlet receives request
information through the ServletRequest object
and sends data back to the client through the
ServletResponse object.

22. destroy() destroy() is also called only once
immediately before the Servlet is
unloaded. It is used to clear all retained
resources such as database connection,
threads, file handles and so on. This
method is overridden in order to free up
any resources being used by the
Servlet.
getServlet
Config()
Provides the ServletConfig object for
initializing the parameters.
getServletI
nfo()
Provides the Servlet metadata such as
author, Servlet version and other
copyright information. This method
needs to be overridden inside the

23. Thank You