Technology Overview

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!!

Servlet code Servlet code Servlet code Anatomy of a Servlet Load Server Server Client Handle Client Requests Client Server Unload

Anatomy of a Servlet • init() • destroy() • service() • doGet() • doPost()

Anatomy of a Servlet • HTTPServletRequest object • Information about an HTTP request • 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 • 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

Technology Overview