OOSSE - OO Review

Review session

A review of other OO technologies and may be useful for exam (not required for assignment)

OO web development philosophy JSP and OO MVC models review

Struts Tag libaries

Ajax Summary

Slide 1Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

OO Software Engineering

By now you have experienced UMLJSP

Let us review the OO tenets (beliefs, principles) and how JSP reflects these tenets

What are the tenets of OO?

Version 1.1 Dec 2008Slide 2Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

UML for web development

Can we also reflect on this?How does UML help in web development

What diagrams have been useful?

What else is available from UML?Answer: Web Application Extensions (WAE)A set of UML modelling aspects designed to help

the web developer model web applicationsReading here

Version 1.1 Dec 2008Slide 3Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

JSP engine reviewed

The JSP engine builds a servlet. The HTML portions of the JavaServer Page

become Strings transmitted to print methods of a PrintWriter object.

The JSP tag portions result in calls to methods of the appropriate class whose output is translated into more calls to a println method to place the result in the HTML document.

Version 1.1 Dec 2008Slide 4Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

JSP engine reviewed

JSP actually supports real Java code, not a new scripting language.

Java code inside JSP is added to methods of a Java Servlet that are generated the first time the JSP is requested.

Uses set of pre-established objects by the Web server that they use to generate a dynamic Web page.

Version 1.1 Dec 2008Slide 5Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

OO web development philosophy

Web development...A collection of individual objects, that act on each other

Different from traditional view in which a program may be seen as a collection of actions, or simply as a list of instructions

Objects capable of receiving messages, processing data, and sending messages to other objects

New object that inherits features from existing objectsWhat we are seeing is a move from scripting/HTML

websites to a more OO philosophy

Version 1.1 Dec 2008Slide 6Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

JSP Model 1 architecture

JSPs to handle HTTP requestsData layer via Java BeansFor small web applications this model is okay

but more complex commercial applications a different model is required – Model 2

Version 1.1 Dec 2008Slide 7Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Version 1.1 Dec 2008Slide 8Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

JSP Model 2 architectureAlso called Web Model-View-Controller (MVC)

design see next slideSeparates the GUI from the business layerUses a Java Servlet to receive the HTTP

requests from the browser and communicate with the model layer

JSPs only used for presentation – the Servlet determines which view to send back to the client

Version 1.1 Dec 2008Slide 9Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Version 1.1 Dec 2008Slide 10Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Servlets - “nuts and bolts”The Servlet class extends the HttpServlet class

Essentially this means it can use the attributes/methods of this class

The HttpServlet class has a number of methodsan init( ) method - used for connecting to databases dsn’sit has service method e.g. doGet, doPost, doPut and doDeletethe above methods are the “meat” of the HttpServlet classIt uses two objects, namely HttpServlet Request and

HttpServlet ResponseHere is an example of the MVC approach <link>

Version 1.1 Dec 2008Slide 11Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Other technology - Apache Struts

Interesting web architecture frameworkhttp://struts.apache.org/Designed to handle requests made by the client or

by web browsers

Apache struts is an open source framework using servlet and JSP

See next slide for picture of struts

Version 1.1 Dec 2008Slide 12Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Version 1.1 Dec 2008Slide 13Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Other technology - Tag Libaries

Custom tags are dynamic page elements.This means they can provide functionality to a

webpage using a syntax similar to normal HTML tags.

The functionality is up to you…They can provide an alternative (or an

additional) mechanism to JavaBeans for dynamic scripting

As an example see this link <JSP Controls>

Version 1.1 Dec 2008Slide 14Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

What do you need?

There are two components to a tag:A Java tag handler class that implements the tag’s

functionality.A Tag Library Descriptor (TLD) in the form of an

XML file describing the tag.

By including this tag on a JSP page you have access to its functionality.

Version 1.1 Dec 2008Slide 15Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Java handler class

Yes, you have to code the functionality in Java.So why bother? Why not just create a

JavaBean instead?For standard webpage scripters, tags are more

familiar and provide a simpler mechanism.For web application developers, JavaBeans

integrate more fully with the full application environment so are more powerful.

Your choice….

Version 1.1 Dec 2008Slide 16Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Tag Library Descriptor

A TLD is a (fairly) simple XML file that describes a set of custom tags.

You can put as many or as few custom tags in a TLD and more than one TLD can be used in a single project.

In principle, you could create many useful tags and zip them into one .jar file for easy resusability.

Version 1.1 Dec 2008Slide 20Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Other technology - Ajax

AJAX, shorthand for Asynchronous JavaScript and XML

exchanging small amounts of data with the server behind the scenes

Speeds up web interaction

Version 1.1 Dec 2008Slide 30Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Version 1.1 Dec 2008Slide 31Source: j.c.westlake@staffs.ac.uk

OOSSE - OO Review

Summary

Doing development in an OO style is beneficial even if the software being used is not directly OO

For the enterprise level OO is evident in the selection of technologies mentioned

Version 1.1 Dec 2008Slide 32Source: j.c.westlake@staffs.ac.uk