This document provides an introduction to servlets and Java EE. It discusses that servlets are used to create dynamic web content by processing HTTP requests in a non-blocking way using Java code. Servlets provide APIs for session management. The document outlines the servlet lifecycle and how servlets work by having the web container create threads to handle multiple requests. It compares GET and POST requests and discusses the servlet API and basic Tomcat setup. The next session will provide a deeper look at HTTP servlets and Java EE.

1. Java & JEE Training
Session 25 – Introduction to Enterprise Java; Servlets

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Agenda
• Introduction to Java EE Continued
• Servlets

3. Java & JEE Training
Introduction to JEE

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Web Server and Application Server

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Enterprise Java – Multi-tier architecture

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Copyright 2002 © Paulo Merson
JSP
• Used for web pages with dynamic content
• Processes HTTP requests (non-blocking call-and-return)
• Accepts HTML tags, special JSP tags, and scriptlets of Java code
• Separates static content from presentation logic
• Can be created by web designer using HTML tools

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Copyright 2002 © Paulo Merson
Servlet
• Used for web pages with dynamic content
• Processes HTTP requests (non-blocking call-and-return)
• Written in Java; uses print statements to render HTML
• Loaded into memory once and then called many times
• Provides APIs for session management

8. Java & JEE Training
Servlets

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What is a Servlet?
• Servlet is a technology i.e. used to create web application.
• Servlet is an API that provides many interfaces and classes including
documentations.
• Servlet is an interface that must be implemented for creating any servlet.

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How does a Servlet work?
• The web container creates threads for handling the multiple requests to the servlet.
Threads have a lot of benefits over the Processes such as they share a common
memory area, lightweight, cost of communication between the threads are low

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HTTP Response Codes
• 200 Series – OK
• 300 Series – Redirecting to another page
• 400 series – User error. E.g. 404 means page not found
• 500 series – Server error. E.g. database is down
W3C standards.

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GET vs POST
GET POST
1) In case of Get request, only limited
amount of data can be sent because data
is sent in header.
In case of post request, large amount of
data can be sent because data is sent in
body.
2) Get request is not secured because
data is exposed in URL bar.
Post request is secured because data is
not exposed in URL bar.
3) Get request can be bookmarked. Post request cannot be bookmarked.
4) Get request is idempotent . It means
second request will be ignored until
response of first request is delivered
Post request is non-idempotent.
5) Get request is more efficient and used
more than Post.
Post request is less efficient and used
less than get.

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Servlet API
• The javax.servlet package contains many interfaces and classes that are
used by the servlet or web container. These are not specific to any
protocol.
• The javax.servlet.http package contains interfaces and classes that are
responsible for http requests only.

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Life Cycle of a Servlet
• As displayed in the above diagram, there are three states of a servlet: new,
ready and end. The servlet is in new state if servlet instance is created.
After invoking the init() method, Servlet comes in the ready state. In the
ready state, servlet performs all the tasks. When the web container invokes
the destroy() method, it shifts to the end state.

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Basic Tomcat Setup
http://crunchify.com/step-by-step-guide-to-setup-and-install-apache-
tomcat-server-in-eclipse-development-environment-ide/
• Follow the steps in the link above

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Topics to be covered in next session
• HTTP Servlets and Java EE a deeper look

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Thank you!