J2EE Overview

1
J2EE Overview

• Web Programming
• CSCI 4300

2
J2EE multi-tier architecture

• Servlet Java class loaded into Web server
• JSP page enhanced HTML page that is compiled
  into a servlet for deployment
• JavaBean data holding class (part of Model in
  MVC)

3
J2EE Architecture

• Applets and special clients downloaded, connect
  back to server
• Enterprise Java Beans long-term,
  application-scope data storage and business logic

4
Web Application Layout
5
Mirroring packages with directories
6
Web Application Descriptor, web.xml

• Defines servlets and maps them to URL paths
• Declares the welcome file for the app
• Specifies pages or servlets to handle various
  errors
• Provides initialization parameters to servlets
• Provides links to external resources such as
  database connections

7
Web.xml prolog

• lt?xml version"1.0" encoding"ISO-8859-1"?gt
• lt!DOCTYPE web-app PUBLIC "-//Sun Microsystems,
  Inc.//DTD Web Application 2.3//EN"
• http//java.sun.com/dtd/web- app_2_3.dtdgt
• You can validate your web.xml using the W3C
  validator service (recommended1)
• When you change your web.xml, you must ask Chris
  or me to reload your web-app

8
Web.xml root element

• ltweb-appgt
• web application contents.
• lt/web-appgt
• Can contain
• Servlet definitions
• Servlet paths
• Parameters
• Etc, etc.

9
Servlet element

• ltservletgt
• ltservlet-namegtGonzoServletlt/servlet-namegt
• ltservlet-classgtcs4300.Gonzolt/servlet-classgt
• lt/servletgt
• Or
• ltservletgt
• ltservlet-namegtGonzoServletlt/servlet-namegt
• ltjsp-pagegtgonzo.jsplt/jsp-pagegt
• lt/servletgt

10
Servlet-mapping element

• ltservlet-mappinggt
• ltservlet-namegtGonzoServletlt/servlet-namegt
• lturl-patterngt/gonzolt/url-patterngt
• lt/servlet-mappinggt
• If the web application root is http//ganesha.cs.u
  ga.edu/myapp,
• GonzoServlet is accessed at
• http//ganesha.cs.uga.edu/myapp/gonzo

11
Welcome page

• ltwelcome-file-listgt
• ltwelcome-filegt
• index.jsp
• lt/welcome-filegt
• lt/welcome-file-listgt
• Index.jsp is the file served at the URL
  http//ganesha.cs.uga.edu/myapp

12
Error page elements

• lterror-pagegt
• lterror-codegt404lt/error-codegt
• ltlocationgtnotFound.jsplt/locationgt
• lt/error-pagegt
• lterror-pagegt
• ltexception-typegt
• org.xml.sax.SaxParseException
• lt/exception-typegt
• ltlocationgtparseError.jsplt/locationgt
• lt/error-pagegt

13
Basic JSP page

• lt_at_ page contentType"text/html charsetUTF-8"
  gt
• lthtmlgt
• ltheadgt
• ltStatic HTML codegt
• Declarations
• Java expressions
• Scriptlets (chunks of Java code)
• Try to minimize the mixing of HTML with Java
  (violates Model 2 architecture)

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Declaration, scriptlet, and expression

• lt! int i String userName gt
• lttable border1gt
• lt for (i0iltuserName.lengthi) gt
• lttrgtlttdgtlti1 gt lt/tdgt
• lttdgt ltuserNamei gt lt/tdgtlt/trgt
• lt gt
• lt/tablegt

15
Equivalent HTML from previous

• lttable border1gt
• lttrgtlttdgt1lt/tdgtlttdgtMichael Adamslt/tdgtlt/trgt
• lttrgtlttdgt2lt/tdgtlttdgtDan Everettlt/tdgtlt/trgt
• lttrgtlttdgt1lt/tdgtlttdgtHunter Thompsonlt/tdgtlt/trgt
• lt/tablegt
• But note that we try to avoid such mixing of Java
  and HTML!

16
Model 2 Architecture (MVC)
17
Helper Object Scopes
18
JavaBean

• Helper class that holds information
• Separates Java code from HTML
• Implements Model component of MVC architecture
• Useful for holding session data

19
JSP Address Book Interface
20
JavaBean Example

• Store functionality user enters name -email pair
  for storage in bean
• Fetch functionality user enters name, bean
  replies with email

21
JSP-Bean communication

• Make ltINPUTgt element names in JSP correspond to
  variable names in Bean
• Write Bean class with setX() and getX() setter
  and getter methods
• ltjspsetPropertygt sends inputs to Bean
• ltjspgetPropertygt gets values from Bean

22
Acknowledgements

• J2EE architecture diagrams Sun J2EE tutorial,
  http//java.sun.com/j2ee/1.4/docs/tutorial/doc/ind
  ex.html
• Object scopes jGuru Java Server Pages
  fundamentals, http//java.sun.com/developer/online
  Training/JSPIntro/contents.htmlJSPIntro6_3