Build a Web Application on J2EE

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Build a Web Application on J2EE
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J2EE Scenario

• Client Web Server EIS Resources
• Client Application Server EIS Resources
• Client Web Server Application Server EIS
  Resources

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Client Web Server EIS Resources
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Business to Business
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Web Application

• A web application is a collection of servlets,
  html pages, classes, and other resources that can
  be bundled and run on multiple containers from
  multiple vendors.
• A Web application is located on a central server
  and provides service to a variety of clients.
• Web applications provide dynamic and interactive
  content to browser-based clients.

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Web Application Environment
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JDK

• All J2EE applications require the Java Developers
  Kit to run Java classes or the Java Virtual
  Machine (JVM).
• Download JDK from java.sun.com for free
• Configure several environment variables.
• JAVA_HOME
• CLASSPATH

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Web Application Structure
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Container

• The container is an independent application that
  creates an environment for web components.

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Functions of Container

• Life cycle management for components.
• Environment configuration.
• Resources.

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Web Container

• An entity that implements the Web component
  contract of the J2EE architecture.
• specify a runtime environment for Web components
  that includes security, concurrency, life cycle
  management, transaction, deployment, and other
  services
• provide the same services as a JSP container and
  a federated view of the J2EE platform APIs.
• can run a Web application that is tagged as
  distributable and that executes across multiple
  Java virtual machines running on the same host or
  on different hosts.

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Web Container Provider

• Open Source
• Tomcat
• Business Product
• WebLogic
• WebShpere

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Tomcat

• Just a JSP, Servlets Container
• jakarta.apache.org/tomcat/index.html

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Application Container

• An entity that implements the Java Classes
  contract of the J2EE architecture.
• Java Classes include
• EJB
• other Java Classes
• access to the J2EE service and communication APIs.

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Application Container Provider

• Open Source
• JBOSS
• Business Product
• WebLogic
• WebShpere
• Silverstream

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Connectors

• The connector is where the abstract really meets
  the concrete.
• A connector is a translator between an enterprise
  information system and the J2EE interfaces.
• Another type of connector, a JNDI Service
  Provider Interface, provides access to naming and
  directory services.

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JDBC

• a JDBC driver, provides access to databases.

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JNDI

• provides access to naming and directory services
• provides a link between Java code and various
  naming and directory services such as Domain Name
  System (DNS), Novell Directory Service (NDS),
  CORBA, and Network Information System (NIS).
• allows you to access code and resources across
  widely separated platforms and directory
  structures through the use of a simple naming
  scheme.

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Tools

• Ant
• IDE
• Jbuilder
• NetBeans

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Data format used in Web Application

• HTML
• JSP
• Image files
• Gif
• JPEG
• Class file
• Source code
• Complied code
• XML
• JAR file used in J2EE for packaging EJBs and
  client-side Java Applications
• WAR file web applications made from Servlets,
  JSPs, and supporting classes
• EAR file contain all of the components that make
  up a particular J2EE application

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Web Application can be exist in

• WAR files
• directory

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Web Application Archive File

• Web applications can be packaged and signed,
  using the standard Java Archive tools, into a Web
  ARchive format (war) file.
• When packaged into such a form, a META-INF
  directory will be present which contains
  information useful to the Java Archive tools.

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Basic Web Application Directory
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Root

• The root of this hierarchy serves as a document
  root for serving files that are part of this
  context.
• For example,
• a web application located at /catalog in a web
  server
• the index.html file located at the base of the
  web application hierarchy can be served to
  satisfy a request to /catalog/index.html.

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WEB-INF

• contains all things related to the application
  that arent in the document root of the
  application
• WEB-INF node is not part of the public document
  tree of the application. No file contained in the
  WEB-INF directory may be served directly to a
  client.

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Contents of the WEB-INF directory

• /WEB-INF/web.xml deployment descriptor
• /WEB-INF/classes/ directory for servlet and
  utility classes.
• /WEB-INF/lib/.jar area for Java Archive files
  which contain servlets, beans, and other utility
  classes useful to the web application.

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Customize Web Application directory
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Web.xml

• The web.xml file format is defined in the Servlet
  Specification, so this file format will be used
  in every servlet-conforming Java servlet
  container.
• This file format is used in two places in Tomcat
  CATALINA_BASE/conf directory
• each web application.

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Deployment description of Web Application

• Web.xml
• The deployment elements that contain this
  information are
• env-entry
• ejb-ref
• resource-ref

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Example of Web.xml

• lt?xml version"1.0" encoding"UTF-8" ?gt
•   lt!DOCTYPE web-app (View Source for full
  doctype...)gt
• - ltweb-appgt
•   ltdescriptiongtOracle Test Applt/descriptiongt
• - ltlistenergt
•   ltlistener-classgtStudentPackage.contextlisenterlt/
  listener-classgt
•   lt/listenergt
• - ltresource-refgt
•   ltdescriptiongtOracle Datasource
  examplelt/descriptiongt
•   ltres-ref-namegtjdbc/myoraclelt/res-ref-namegt
•   ltres-typegtjavax.sql.DataSourcelt/res-typegt
•   ltres-authgtContainerlt/res-authgt
•   lt/resource-refgt
•   lt/web-appgt

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Configure resources used by Web Application

• use Server.xml to configure resources
• Web container runs in an object-oriented way
• dynamically builds its object structure at
  runtime, based on the configuration files
• each major element in the server.xml file creates
  a software "object," and the ordering and nesting
  of these elements sets up processing pipelines
  that allow you to perform filtering, grouping.

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Context in server.xml

• A Context represents one web application within a
  Tomcat instance.
• the web site is made up of one or more Contexts.

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key attributes in a Context
Attribute Meaning
crossContext Specifies whether ServletContext.getContext(otherWebApp) should succeed (true) or return null (false)
debug Debugging level
docBase URL relative to virtual host
path Absolute path to the directory
privileged Specifies whether this context can run Container servlets, such as the Manager application
reloadable Specifies whether servlet files on disk will be monitored, and reloaded if their timestamp changes
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Example of Server.xml

• lt!-- buzzinservlet --gt ltContext path"/buzzin"
  docBase"/home/ian/javasrc/threads/buzzin"
  debug"0" reloadable"true"gt lt/Contextgt