Basic Java Servlet/JSP Web Development

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Basic Java Servlet/JSP Web Development

• David Lucek
• Lucek Consulting
• www.lucek.com
• dave_at_lucek.com

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Download the Sample Application

• Download from www.lucek.com, select the downloads
  tab
• Includes the full source
• Unzip to c\ drive or HOME/lucek

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What is a Servlet?

• Java Servlets/JSP are part of the Suns J2EE
  Enterprise Architecture
• The web development part
• Java Servlet
• is a simple, consistent mechanism for extending
  the functionality of a web server
• Are precompiled Java programs that are executed
  on the server side.
• Require a Servlet container to run in
• Latest Servlet Spec is 2.3

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What is a Java Server Page (JSP)

• Java Server Pages (JSP)
• A simplified, fast way to create dynamic web
  content
• HTML or XML pages with embedded Java Code or Java
  Beans
• Can be a mix of template data in HTML/XML with
  some dynamic content
• A JSP is a complied to a Java Servlet
  automatically by the Servlet container, it is
  then cached
• Latest JSP Spec is 1.2

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Why Use Servlets?

• Work well in a Heterogeneous Environments
• OS and platform neutral
• Work with all major web servers (IIS,
  Apache,etc..)
• Well defined Web Architecture framework
• Standard built in services such as
• Standard Approach to Authentication using
  declarative security vice programmatic security
• Database connection pooling
• Complete support for sessions via cookies and/or
  URL re-writing
• Has automatic fallback to URL re-writing

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Why Use Servlets Cont?

• Robust Object-Orientated API in Java language
• Ever try to maintain a large ASP, Perl, or PHP
  site ?
• Clean separation of Controller/Logic from
  Presentation
• Efficient, scales very well
• There are good free Servlet/JSP containers and
  connectors
• That run under both UNIX and win32

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J2EE Web Application Components

• Java Servlets
• Extend off of HttpServlet
• JSP pages, normally for Presentation
• Java Beans
• Normally used as value objects, pass to data to
  JSPs
• Tag Libraries XML based JSP elements
• Web Deployment Descriptor
• /web-inf/web.xml

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Web Deployment Descriptor

• /web-inf/web.xml
• Part of the standard
• Defines servlets used in the web application
• Maps servlets to URLs
• A servlet can map to many URLs
• Defines resources available to the web app
• Defines security constraints
• Defines other stuff like
• Welcome file list
• Session timeout
• Error page mapping

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J2EE Web Directory Structure 1

• Top Directory is normally the context Path
• /tomcat/webapps/servletdemo
• Normally, the URL would be http//localhost8080/s
  ervletdemo
• Contains JSP and other static content plus the
  web-inf directory
• /web-inf directory
• This is a protected directory, can not point
  browser to any file in this directory
• /classes unpacked web application classes,
  auto-magically added to CLASS_PATH
• /lib web application JAR files
• /taglib tag library descriptor files

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J2EE Web Directory Structure 2

• /web-inf/web.xml
• /web-inf/
• Would normally put any static or JSP files here
• Protects them from Direct Invocation
• Always best to call a JSP through a servlet first

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JSP Constructs 1

• Used in JSP pages, pages that end .jsp
• Comment lt-- Comment --gt
• Declaration lt! int x 0 gt
• Expression lt expression gt
• Outputs to the Response stream
• Like a printf to the browser
• Do NOT use semi-colon to terminate the line
• Scriplets - contains Java Code
• lt code fragments gt

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JSP Constructs 2

• lt if (value.getName().length ! 0) gt
• ltH2gtThe value is lt value.getName() gtlt/H2gt
• lt else gt
• ltH2gtValue is emptylt/H2gt
• lt gt
• Implicit objects always available in the JSP
  Page
• request Browsers Request Object
• Use to get HTTP headers, length etc..
• response - HttpResponse Object

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JSP Constructs 3

• session internal HttpSession Object
• pageContext
• application
• out, same as lt gt
• config servlet configuration
• page
• exception
• JSP Directives
• Are messages or instructions to the JSP container

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JSP Constructs 4

• Do not produce any output
• page directive
• lt_at_ page importcom.lucek. gt
• Commonly used for importing class paths
• include directive
• lt_at_ include fileheader.htm gt
• Good for including static content
• taglib lists the tag library descriptor
  location
• Required when using tab libraries

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Java Beans as Used in Web Apps

• Normally used for all data transfers and business
  components
• Similar to how Java Beans are used in Swing and
  AWT
• But do not need the full implementation
• Must have no constructor or no-arg constructor
• Must have setter and getter methods for each
  property value
• JSP constructs/tags use Java Beans

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JSP Actions

• JSP actions are special tags that affect the
  output stream and are normally used with Java
  beans
• Most commonly used
• ltjspuseBeangt, ltjspgetPropertygt,
  ltjspsetPropertygt
• The code below will display the lastName property
  of the student bean on the output stream
• ltjspuseBean id"student" scope"request"
  class"com.lucek.dto.StudentValue" /gt
• ltjspgetProperty name"student"
  property"lastName" /gt

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Servlet Container/Engine

• Servlets/JSP require a Container
• Apache Tomcat is the reference implementation of
  the Servlet/JSP Specs
• It is open source, small, install quickly,and is
  FREE
• Latest Version is 4.1.24
• Web Site jakarta.apache.org/tomcat
• It include a simple HTTP 1.1 server, good enough
  for development and small intranets.

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Tomcat Install

• Requires a JDK, get 1.4.1 and install into c\jdk
  or HOME/jdk
• Add JAVA_HOME to your environment and the bin
  directory to your PATH
• Good practice to unpack into c\tomcat or
  HOME/tomcat
• Add CATALINA_HOME to your environment and the
  bin directory to your PATH

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Tomcat Directory Structure

• Everything is relative to CATALINA_HOME
• /bin Startup/shutdown scripts
• /conf
• Server.xml main configuration file
• /common common class and jar files used by
  Tomcat and web applications
• Put JDBC drivers here
• /server class and jar files used by Tomcat
  internally
• /shared class and jar files for all web
  applications
• /webapps This is where you put your web
  application in a sub-directory or external
  context file.

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Starting Tomcat

• /bin/startup.bat or startup.sh
• Point Browers to http//localhost8080, should
  see default page
• All the Docs are there on the default page!
• Check out the examples pages, good tutorials

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Other Development Tools 1

• Ant Build Tool
• Standard Java Build tool
• Basic on UNIX make, but much better
• Site http//ant.apache.org
• Install in c\ant or HOME/ant
• Java IDE
• Try NetBeans, it is nice
• Tomcat is built in, but is an older version
• Includes full Servlet and JSP debugging
• Site www.netbeans.org

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Other Development Tools 2

• Junit
• Standard Automated Unit Testing Tool
• Site http//junit.sourceforge.net
• Jedit
• Slick Programmers Editor
• Written in Java
• Site jedit.org

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Simple Servlet Application 1

• See servletdemo code
• Mount the servletdemo, servletdemo/java/src, and
  servletdemo/web in NetBeans Explorer Tab
• For a Hello World Servlet look at
• Java/src/com/lucek/action/HelloWorld.java
• To build and run
• cd servletdemo
• Setup the proper build variables in the
  build.properties file
• ant all
• ant deploy
• Point your browsers at http//localhost8080/servl
  etdemo

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Simple Servlet Application 2

• Look at the web.xml file and how the same servlet
  can be mapped to many URLs
• Look at SimpleBean.java which should how to pass
  a Java Bean to a JSP page
• Look at the different ways a beans value can be
  obtained in the EditStudent.jsp

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Best Practices/Patterns

• Always Separate out the logic from the
  presentation
• Use servlets for the logic/controller and JSPs
  for presentation
• Ideally should never have Java Code in the JSP
  page
• Have a clean separation between your data access
  and controller layers (DAO)
• Always use DTO or value object
• Use a Model-View-Controller Architecture
• Do not write it, use Struts
• Site jakarta.apache.org/struts/
• Use Unit tests
• Junit Automation via Ant build tasks

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What we have not talked about

• All the specific Servlet APIs
• Tag libraries
• Sessions, cookies
• JDBC service support from the container
• Container based authentication
• Lots of other stuff

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Next Presentation?

• Create a data driven web site using MySql and
  Servlets/JSP
• Setup Authentication Realm with declarative
  security
• Setup JDBC connection pooling
• Struts?