Servlets allow servers to generate dynamic web page content. Servlets are Java programs that run on web servers to respond to client HTTP requests by generating documents like HTML pages. Servlets extend server functionality beyond static pages by enabling content generation, secure access, database interaction, and session tracking for each client. The servlet container receives requests and directs them to servlets, which process requests and return responses like HTML documents to clients. Servlets offer advantages over CGI like better performance since they run within the server address space rather than as separate processes.

1. Advanced Programming
Servlets as Introduction
Gera
2020
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2. Servlets
• HTML (Hyper Text Markup Language) is the tagging
language used to create Web pages.
• HTML alone can only be used to create static Web pages
⎯ pages whose content is determined at the time of
writing and which never changes.
• Though this is perfectly adequate for some applications,
an increasing number of others have a requirement for
dynamic web pages ⎯ pages whose content changes
according to the particular user or in response to
changing data.
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3. Servlets…
•Some dynamic web pages common examples are
listed below.
• Results of a real-time, online survey.
• Results of a search operation.
• Contents of an electronic shopping cart.
•One powerful and increasingly popular way of
satisfying this need is to use Java servlets.
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4. Servlets…
•A servlet is a program written in Java that runs on
a Web server. It is executed in response to a
client's (i.e., a browser's) HTTP request and creates
a document (usually an HTML document) to be
returned to the client by the server.
•It extends the functionality of the server, without
the performance limitations associated with CGI
programs.
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5. Servlets…
•All the major Web servers now have support for
servlets.
•Servlets extend a server’s functionality by allowing
the server to generate dynamic content.
•For instance, servlets can dynamically generate
custom XHTML documents, help provide secure
access to a website, interact with databases on
behalf of a client and maintain unique session
information for each client.
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6. Servlets…
•A web server component called the servlet
container executes and interacts with
servlets.
•Packages javax.servlet and javax.servlet.http
provide the classes and interfaces to define
servlets.
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7. Servlets…
•The servlet container receives HTTP requests from
a client and directs each request to the
appropriate servlet.
•The servlet processes the request and returns an
appropriate response to the client — usually in the
form of an XHTML or XML (Extensible Markup
Language) document to display in the browser.
XML is a language used to exchange structured
data on the web.
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8. Servlets…
• Java Servlets are programs that run on a Web or
Application server and act as a middle layer between a
requests coming from a Web browser or other HTTP
client and databases or applications on the HTTP server.
• Using Servlets, you can collect input from users through
web page forms, present records from a database or
another source, and create web pages dynamically.
• Java Servlets often serve the same purpose as programs
implemented using the Common Gateway Interface
(CGI).
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9. Servlets…
But Servlets offer several advantages in comparison with the CGI.
• Performance is significantly better.
• Servlets execute within the address space of a Web server. It is not
necessary to create a separate process to handle each client
request.
• Servlets are platform-independent because they are written in Java.
• Java security manager on the server enforces a set of restrictions to
protect the resources on a server machine. So servlets are trusted.
• The full functionality of the Java class libraries is available to a
servlet. It can communicate with applets, databases, or other
software via the sockets and RMI mechanisms that you have seen
already. 9

10. Servlets Architecture
• The following diagram shows the position of Servlets in a
Web Application.
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Web Browser
HTTP
Server
Servlets
Program
Database
HTTP
Protocol

11. Servlets Tasks
•Read the explicit data sent by the clients
(browsers). This includes an HTML form on a Web
page or it could also come from an applet or a
custom HTTP client program.
•Read the implicit HTTP request data sent by the
clients (browsers). This includes cookies, media
types and compression schemes the browser
understands, and so forth.
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12. Servlets Tasks…
•Process the data and generate the results. This
process may require talking to a database,
executing an RMI or CORBA call, invoking a Web
service, or computing the response directly.
•Send the explicit data (i.e., the document) to the
clients (browsers). This document can be sent in a
variety of formats, including text (HTML or XML),
binary (GIF images), Excel, etc.
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13. Servlets Tasks…
• Send the implicit HTTP response to the clients (browsers). This
includes telling the browsers or other clients what type of
document is being returned (e.g., HTML), setting cookies and
caching parameters, and other such tasks.
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14. References
➢S. Horstmann and Gary Cornell, Core Java 2 – Volume II-
Advanced Features, Sun Microsystems Press
➢Harvey M. Deitel and Paul J. Deitel, Java How to
Program, Deitel & Associates
➢Tutorials Point “Java Servlets: web application
framework,” www.tutorialspoint.com
➢Jan Graba, “An Introduction to Network Programming
with Java, ” Faculty of ACES, Sheffield Hallam University,
UK, 2007.
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Gerabirhan Paulos
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