Transcript JAVA servlets

Technology Overview
JAVA Servlets
CS-611
S. Witherspoon
JAVA Servlets
What are servlets
 Why use them
 Anatomy of a servlet
 Sample servlets
 Servlets & J2EE

Servlet paradigm
Description
Servlets are the Java platform
technology of choice for extending
and enhancing web servers
 Servlets are programs that run on a
Web server and build Web pages
based on data:

• Submitted by user
• Data that changes frequently
• Data from corporate databases or other
sources
HTTP servlet
Advantage of Servlets Over CGI

Efficient
• Runs in the Java Virtual Machine
• Each request is handled by lightweight
thread
• Only 1 copy of servlet class in memory
• Optimization alternative ( caching
previous computations, keeping
database connections open)
Advantage of Servlets Over CGI

Convenient
• Extensive infrastructure for
automatically parsing and decoding
HTML form data, reading and setting
HTTP headers, handling cookies,
tracking sessions
• Servlets receive all the benefits of the
JAVA language (portability,
performance, reusability and crash
protection)
Advantage of Servlets Over CGI

Powerful
• Servlets have access to the entire
family of JAVA APIs, including JDBCTM
API to access enterprise databases
• Servlets can talk directly to Web servers
• Servlets can talk and share data with
each other
Advantage of Servlets Over CGI

Inexpensive
• Adding server support to your web
server is inexpensive of free (Apache
Tomcat)

Disadvantage??
You must learn Java!!
Anatomy of a Servlet
Server
Servlet code
Servlet code
Server
Handle
Client
Requests
Servlet code
Server
Unload
Load
Client
Client
Anatomy of a Servlet
init()
 destroy()
 service()

• doGet()
• doPost()
Anatomy of a Servlet

HTTPServletRequest object
• Information about an HTTP request
•
•
•
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
Headers
Query String
Session
Cookies
HTTPServletResponse object
• Used for formatting an HTTP response
• Headers
• Status codes
• Cookies
Sample Servlets
Servlet Examples (localhost)
or
CSDateTime Demo (remote host)
Sample Servlet (source code)
Sue Example
CSDateTime
Software Setup

Directory Structure
<tomcat base>/webapps/ROOT/WEB-INF/classes

Environment Variables
JAVA_HOME
J2EE_HOME
CLASSPATH=$JAVA_HOME/jre/lib/

Path Settings
PATH=$JAVA_HOME/bin:$J2EE_HOME/bin:$PATH
Compiling the Servlet
Sun ONE Studio
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•
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Open <servlet code>.java
Select Compile under Build menu
Copy resultant <servlet code>.class file to :
<tomcat base>/webapps/ROOT/WEB-INF/classes
w/o JAVA ToolKit
cd <tomcat base>/webapps/ROOT/WEB-INF/classes
javac <servlet code>.java
Running the Servlet
Make sure Web Server (Tomcat) is
running
 Bring up Web Browser
 Bring up Servlet

http://localhost:<port>/servlet/<servlet code>
Enterprise Servlets and J2EE
Enterprise Servlets and J2EE

Distributed Environment (rules of thumb)
• Instance variables and static variables should not be
used to store state
• The context should not be used to store application
state
• Any object placed into an HttpSession should be
capable being moved to a different machine
• Avoid using java.io package for file access, use
getServletContext().getResource()
• Syncrhonization is not global and works only for the
local JVM