ComparativeDisplayTechnologies

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Transcript ComparativeDisplayTechnologies 

Comparative Display
Technologies in Sakai
Aaron Zeckoski
[email protected]
Sakai Oxford Tetra ELF Workshop
Creative Commons AttributionShareAlike 2.5 License
Sakai Programmer's Café
What do we want out of
a display technology?
• Easy to use for the developer
• Good separation of Code and UI
–i.e. easy to use for the UI designer
• Good integration with Sakai
–Portal, widgets, tools, etc…
2
What technologies work
• Virtually any Java related display technology
can work in Sakai
• There are some caveats
– Sakai uses a special Servlet to handle redirects
and processing of HTTP request variables
– Portal and widget interaction have to be
developed for each technology
• Bottom line: You are better off sticking with
the ones that currently work
3
What games are
there in town?
http://java.sun.com/products/servlet/
http://jakarta.apache.org/velocity/
http://java.sun.com/products/jsp/
JSF
http://java.sun.com/javaee/javaserverfaces/
http://www2.caret.cam.ac.uk/rsfwiki/
But there are a few things to consider…
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Java Servlets Intro
• modules of Java code that run in a
server app to answer client requests
• HTML is hardcoded in the Java class
– It can be pulled from external files though
• Most more advanced technologies are
built on Servlets
• Sakai uses Servlet API 2.4
URL: http://en.wikipedia.org/wiki/Java_Servlet
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Code Snippet
package org.java.helloworld;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloWorld extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
PrintWriter out = response.getWriter();
out.println("Hello World");
}
}
URL: http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/Servlet-Tutorial-First-Servlets.html
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Java Servlets +
• Tried and tested technology (1997)
• Runs on the server instead of on the
client like an applet
• Pure Java code
• Session tracking via HttpServlet
• Works fine in Sakai
– Café Servlet Hello World sample code
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Java Servlets •
•
•
•
•
Invented in 1997 for goodness sake!
HTML is placed in the Java class
Impossible for UI designers to work with
Poor separation of UI and Code
Development this way is painful and
slow compared to more modern
methods
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Java Servlets Final
• Why would you want to write pure
Servlets any more considering the many
better options out there?
• You are going to use Servlets anyway
but at least use something along with it
• Bottom line: Don’t use this unless you
just want to put an existing Servlet app
into Sakai
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Velocity Templates Intro
• Java based template engine
• Uses “references” to place dynamic
content in html pages with # or $ vars
– Somewhat similar to PHP or JSP
• Meant to allow UI designers to work
alongside programmers
• Apache project
URL: http://jakarta.apache.org/velocity/
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Code Snippet
<HTML>
<HEAD><title>Velocity Sample</title></HEAD>
<BODY>
<h1>Hello $user.name</h1>
<table>
#foreach( $item in $items )
#if ( $itemCheck($item) )
<tr>
<td> $item.value </td>
</tr>
#end
#end
</table>
</BODY>
</HTML>
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Velocity Templates +
• Uses “references” to place dynamic
content in html template pages
– Somewhat similar to PHP or JSP
• Most used display technology in Sakai
– Integration with Sakai is good
• Ok separation of UI and Code
• Decent docs and community
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Velocity Templates • The current Velocity implementation in
Sakai is a custom and out of date
version
• Integration with Sakai is OK but not
really being worked on much anymore
• New development in Velocity is
discouraged by the community
• Mostly carried over from CHEF
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Velocity Templates Final
• Go for technologies that provide better
separation between Code and UI
• Bottom line: You are better off not
using this, only use this if you have
existing apps and cannot rewrite them
14
Java Server Pages Intro
• Dynamic Java web content scripting
language
– Very similar to PHP
• JSP pages are compiled into Servlets
when accessed
• Pages are a mixture of HTML, taglib
tags, and Code
URL: http://java.sun.com/products/jsp/
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Code Snippet
<HTML>
<HEAD><title>JSP Sample</title></HEAD>
<BODY>
<h1>Hello <%= user.getName() %></h1>
Today is <%= new Date() %><br/>
<ul>
<% for (int i=0; i<items.size(); i++) { %>
<li><%= ((Item)items.get(i)).getValue() %></li>
<% } %>
</ul>
</BODY>
</HTML>
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Java Server Pages +
• Easy to develop in and work with
• Can be changed without restarting
• Works fairly well in Sakai
– JSP support is available via a cool Servlet
by Andrew Thornton (Cambridge)
– Used in Rwiki (sorta), XML version
• Well tested technology with large
community
• Excellent docs and many books
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Java Server Pages • Mixes code and HTML together
– Poor separation of code and UI design
• Compiled when accessed
– This can cause a noticeable delay when
accessing a page for the first time
• Integration with Sakai is poor
• Has many of the same weaknesses that
other scripting languages have
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Java Server Pages Final
• JSP support in Sakai is not great yet
• It is difficult for UI designers
• Bottom line: Use this if you have
existing JSP code, but go for options
that provider better separation between
UI and Code for new projects
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Java Server Faces Intro
JSF
• A Java based set of APIs for managing
state, handling events, and defining
navigation
• Mostly builds on JSP
– Though it can be used without JSPs
• Includes a custom set of tag libraries
• Includes error handling, input validation,
and internationalization support
URL: http://java.sun.com/javaee/javaserverfaces/
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Code Snippet
JSF
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<html>
<head><title>JSF sample</title></head>
<body>
<f:view>
<h1><h:outputText value=“Hello #{user.name}"/></h1>
<h:dataTable id=“items"
value="#{itemsBean.items}" var=“item">
<h:column>
<h:outputText value="#{item.value}" />
</h:column>
</h:dataTable>
</f:view>
</body>
</html>
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Java Server Faces +
JSF
• The second most used display
technology in Sakai (after Velocity)
– Used for the portal and a small number of
apps (Gradebook, Assignments, etc…)
• Integrates well with Sakai
– better than any of the other current
solutions (for now)
• MyFaces and Oracle ADF Faces
• Pretty good docs and books
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Java Server Faces -
JSF
• Pretty heavyweight and has problems in
the current version
– These might be fixed in the upcoming
version
•
•
•
•
•
Poor separation of UI design and code
High learning curve
Difficult to use and not very flexible
Poor AJAX/Javascript integration
Does not work with browser navigation
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Java Server Faces Final
JSF
• Most new apps in Sakai are written in
this but it is recognized as having many
weaknesses
• High learning curve and difficulty of use
means slow development
• Bottom line: Don’t use this unless you
really have to, even if you have existing
code
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Reasonable Server Faces
• Spring based web programming
framework
• Uses pure XHTML templates, clean
separation of UI and Code
• Lightweight and pure bean
programming
• Works well with AJAX and Javascript
URL: http://jakarta.apache.org/velocity/
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Code Snippet
<html>
<head><title>RSF sample</title></head>
<body>
<h1>Hello <span rsf:id=“user-name”>User Name</span></h1>
Today is <span rsf:id=“current-date”>1/1/2006</span><br/>
<table>
<tr rsf:id=“items:”>
<td rsf:id=“item-value”>item value here</td>
</tr>
</table>
</body>
</html>
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Reasonable Server Faces +
• Uses pure XHTML templates
– Provides clean separation of UI and Code
• Respects the HTTP request cycle
– Back button works!
• Works well with AJAX and Javascript
• Sakai integration and features are
improving rapidly
• Good docs and code samples available
on the RSF Wiki
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Reasonable Server Faces • Greater separation of UI and code can
require more files and lines of code
– This is true of other solutions as well
• Not used in Sakai core yet but is fully
functional in it and integrates somewhat
– Some code in Sakai Contrib (rsf gallery)
• Small user community
• Still in development (also a positive)
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Reasonable Server Faces Final
• The only really good separation of UI
design and Code available
• Community support is growing and
Sakai integration improving
• Bottom line: Use of this is
recommended for new Sakai apps
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Summary
JSF
•
•
•
•
•
No plain Servlets
Velocity discouraged
JSP ok for small stuff
JSF is just bad
RSF recommended
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