Web Information Systems
Web Application Frameworks
Prof. Beat Signer
Department of Computer Science
Vrije Universiteit Brussel
http://vub.academia.edu/BeatSigner
2 December 2005

Web Application Frameworks
A web application framework is a software framework
that is designed to support the development of
dynamic websites, Web applications and Web
services. The framework aims to alleviate the
overhead associated with common activities
performed in Web development. For example, many
frameworks provide libraries for database access,
templating frameworks and session management, and
often promote code reuse.
[http://en.wikipedia.org/wiki/Web_application_framework]
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 2

Web Application Frameworks ...
 A web application framework supports the development
of dynamic websites, Web Services or web applications
 offers libraries and tools to deal with web application issues
- template libraries
- session management
- database access libraries
 Some frameworks also offer an abstraction from the
underlying enabling technologies
 Leads to faster and more robust development process
 Many frameworks follow the Model-View-Controller
(MVC) design pattern
 no mix of application logic and view (as for example done in JSP)
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 3

Model-View-Controller (MVC)
 Business logic handled by the model
 when the state of a model changes, it notifies its views
- a model can have multiple views
 Design aspects handled by the view
 renders the data of the model
 notifies the controller about changes notifies
View
 Controller handles requests selects view
 processes input and modifies Controller gets
the model state notifies
Model
modifies
state
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 4

Apache Struts 2
 Free open source framework for creating enterprise-
ready Java-based web applications
 Brings the MVC pattern into a web application framework
 model
- Java beans and other helper classes
- completely up to the developer how to implement the model
 view
- template-based approach often based on JavaServer Pages (JSP) in
combination with tag libraries
 controller
- based on Java Servlet technology in combination with filters
 Standard development process for any Struts 2 web
application
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 5

Apache Struts 2
 Simplifies web development
 conventions over configuration
 reasonable default values reduce size of configuration files
 Action-based MVC2 (Pull MVC) framework
 MVC2 slightly different from MVC
- model represented by Action (POJO); view can pull information from the action
 separation of application logic (POJOs) and view components
 ValueStack
 temporary objects, Action objects, ...
 access from JSP via Object Graph Navigational Language (OGNL)
 Multiple view alternatives
 JSP, XSLT, Velocity, ...
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 6

Apache Struts 2 MVC2
View
6 JSP
1 4
Browser Controller
Servlet 5
3
Model
2
JavaBeans
Database
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 7

Apache Struts 2 ...
 Apache Struts does not require any changes to the
servlet container
 regular servlet application
 Fosters modularity and loose coupling
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 8

Apache Struts 2 Architecture
 Servlet request
 standard filter chain
- interception of requests and
responses
- reusable modular units
- e.g. XSLT transformation
 FilterDispatcher consults
controller (ActionMapper)
 ActionProxy is called if
action has to be executed
 consult Configuration-
Manager
 create ActionInvocation
[http://struts.apache.org/2.x/docs/architecture.data/Struts2-Architecture.png]
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 9

Apache Struts 2 Architecture ...
 invoke any interceptors
(controller) before Action
 Action class updates the
model
 ActionInvocation does
a lookup for the Result
 based on Action result code
 mappings in struts.xml
 Result execution (view)
 often based on JSP template
 interceptors in reverse order
 Send response
[http://struts.apache.org/2.x/docs/architecture.data/Struts2-Architecture.png]
 filter chain
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 10

Apache Struts 2 web.xml
<web-app id="WebApp1" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<filter>
<filter-name>struts</filter-name>
<filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
<init-param>
<param-name>actionPackages</param-name>
<param-value>be.ac.vub.wise</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>struts</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<taglib>
<taglib-uri>/WEB-INF/struts-bean.tld</taglib-uri>
<taglib-location>/WEB-INF/struts-bean.tld</taglib-location>
</taglib>
...
</web-app>
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 11

Tag Libraries
 Introduced to encapsulate reusable Java objects in JSP
 provide access to methods on objects
 Apache Struts 2 offers four different libraries
 HTML
- e.g. buttons, form fields, ...
 Template
 Bean
- e.g. definitions, parameters,
 Logic
- e.g. comparisons, ...
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 12

Apache Struts 2 Hello World Example
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<head>
<title>Hello World</title>
</head>
<body>
<h1><s:property value="message"/></h1>
<p>Time: <b><s:property value="currentTime" /></b></p>
</body>
</html>
HelloWorld.jsp
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 13

Apache Struts 2 Hello World Example ...
package be.ac.vub.wise;
import com.opensymphony.xwork2.ActionSupport;
import java.util.Date;
public class HelloWorldImpl extends ActionSupport {
public static final String MESSAGE = "Hello World!";
private String message;
public String execute() throws Exception {
setMessage(MESSAGE);
return SUCCESS;
}
public void setMessage(String message){
this.message = message;
}
public String getMessage() {
return message;
}
public String getCurrentTime(){
return new Date().toString();
}
}
HelloWorldImpl.java
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 14

Apache Struts 2 Hello World Example ...
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<constant name="struts.enable.DynamicMethodInvocation" value="false"/>
<constant name="struts.devMode" value="true"/>
<package name="wise" namespace="/wise" extends="struts-default">
<action name="HelloWorld" class="be.ac.vub.wise.HelloWorldImpl">
<result>/pages/HelloWorld.jsp</result>
</action>
...
</package>
...
</struts>
struts.xml
 Execute the Hello World example by send a request to
 http://localhost:8080/wise/HelloWorld.action
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 15

Adobe Flex
 Adobe's software development kit for cross-platform Rich
Internet Applications (RIAs) based on Adobe Flash
 Two main components
 Adobe Flash player 9 runtime environment
 Free Flex SDK
- compiler and debugger, the Flex framework and user interface components
 Adobe Flex Builder (commercial)
- Eclipse plug-in with MXML compiler and debugger
 Separation of user interface and data
 user interfaces described in MXML markup language in
combination with ActionScript
- similar to AJAX funtionality discussed earlier
- compiled into flash executable (SWF)
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 16

Microsoft Silverlight
 Microsoft's platform for Rich Internet Applications
 Runtime requires a browser plug-in
 Internet Explorer, Firefox and Safari
 Silverlight Core Common Language Runtime (CoreCLR)
 A Silverlight application consists of
 CreateSilverlight.js and Silverlight.js
- initialise the browser plug-in
 user interface described in the Extensible Application Markup
Language (XAML)
- XAML files not compiled  indexable by search engines
 code-behind file containing the program logic
 Programming based on a subset of the .NET Framework
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 17

Microsoft Silverlight ...
 Silverlight 3 introduced a set of powerful new
features including
 LocalConnection API
- communicate asynchronously with multiple applications on the same machine
 out-of-browser experiences
- Silverlight applications can be installed locally for accessing them offline
- cross-platform with Windows/Mac
 Two types of Silverlight web requests
 WebClient class
- OpenReadAsync (for streaming), DownloadStringAsync as well as uploads
 WebRequest
- based on HttpWebRequest
- register asynchronous callback handler
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 18

Microsoft Silverlight ...
 Becoming a competitor to Adobe Flash
 Moonlight is an open source implementation of Silverlight
and is developed as part of the Mono project
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 19

OpenLaszlo
 Open source RIA platform
 Two main components
 LZX programming language
- XML and JavaScript
 OpenLaszlo Server
 The Open Laszlo Server compiles LZX applications into
different possible runtime components
 Java Servlets
 DHTML
 binary SWF files
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 20

Ruby on Rails
 Open source web application framework
 Combination of
 dynamic, reflective, object-oriented programming language Ruby
- combination of Perl-inspired syntax with "Smalltalk" features
 web application framework Rails
 Based on MVC architecture pattern
 The scaffolding feature offered by Rails can
automatically generate some of the models and views
that are required for a website
 developer has to run an external command to generate
Ruby code
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 21

Ruby on Rails
 Ruby on Rails Philosophy
 Don't Repeat Yourself (DRY)
- information should not be stored redundantly (e.g. do not store information in
configuration files if the data can be automatically derived by the system)
 Convention over Configuration (CoC)
- programmer only has to specify unconventional application settings
(e.g. naming conventions to automatically map classes to database tables)
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 22

Video: Ruby on Rails
http://media.rubyonrails.org/video/rails_blog_2.mov
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 23

Web Content Management Systems
 Content management systems that focus on web content
 Main functionality
 data storage and publishing, user management (including access
rights), versioning, workflows
 Offline (create static webpages), online (create
webpages on the fly) and hybrid systems
 Often some kind of server-side caching
 Suited for non-technical users since the underlying
technology is normally completely hidden
 Web CMS Examples
 Joomla, Drupal, ...
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 24

References
 Apache Struts 2
 http://struts.apache.org/2.x/
 Microsoft Silverlight video
 http://silverlight.net/learn/videos/silverlight-videos/net-ria-services-
intro/
 Ruby on Rails Video: Creating a Weblog in 15 Minutes
 http://media.rubyonrails.org/video/rails_blog_2.mov
November 5, 2009 Beat Signer - Department of Computer Science - bsigner@vub.ac.be 25

Next Week
Semantic Web
2 December 2005