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In March 2001, Sun Microsystems released the first beta version of Sun Java Center J2EE Patterns. The J2EE patterns describe the typical problems encountered by enterprise application developers and document a pattern, or abstract solution, to these problems. The J2EE patterns are an important contribution to the industry because they provide developers with a common nomenclature and abstract solutions to recurring problems.

One recurring problem that all enterprise applications have in common is how to present data to the client. Do you use JSPs or Servlets? How do you effectively separate presentation from business logic? How can you support multiple devices without duplicating code? How do you avoid making multiple modifications to your application every time you make a change to your view layout?

J2EE Composite View

One design solution being put forth by Sun's J2EE patterns is the Composite View Pattern. "This solution provides for the creation of a composite view based on the inclusion and substitution of modular dynamic and static template fragments. This solution also promotes the reuse of atomic portions of the View, and encourages modular design. It is appropriate to use a composite view to generate displays containing pluggable atomic components that may be combined in a variety of ways. This scenario occurs, for example with portal sites that include numerous independent views, such as news feeds, weather information, and stock quotes on a single page. There may be a runtime overhead associated with this pattern, and it is the tradeoff for the pattern's improved flexibility.

A system typically has many views, some of which rely on similar atomic pieces of the display to be presented in alternate ways, such as in different locations on the screen or containing modified text. An example is a customer inventory table that is used on multiple pages, surrounded by different information on each page. Another example is a page that includes a header and footer. If each atomic subcomponent is coded directly into the main view in which it is included, the result is duplicate code that is difficult to modify and maintain.

When a component piece is coded directly into the view in which it is used, a change to that subcomponent requires changing each view that contains the subcomponent, requiring multiple modifications to make a single change."1

A Proven Implementation

Jaydoh's HTML Template Mechanism is a fully functioning implementation of the J2EE Composite View pattern and specifically targets the presentation problems detailed above.

Jaydoh's Template mechanism was created to promote the rapid development and easy maintenance of web based applications. The Template subsystem provides a modular mechanism that allows web applications to be built with a consistent look and feel with the capability of producing dynamic HTML content.

HTML templates also offer a clean separation between presentation and the business logic. By decoupling the details of the HTML from the backend Java^TM services, those stronger on web design can focus on the look and feel of the web site without having to learn Java or another programming language. Conversely, those strong in programming can focus on the development of the backend Java services and business logic without any knowledge or worry about how the results will be presented in HTML. In other words, multiple parties can now work in parallel to reduce development time. Changes are also easier to implement since a change in the business logic will not affect the presentation or look and feel of the application and vice versa.

Principals of Jaydoh's Template Mechanism:

1. Developer's develop and Graphic Designers design.

• No scripting is required in the templates (although, we do support JSP markup if you choose to code in the template). One and only one tag is introduced -- this tag has one attribute: name.

• No assumptions are made regarding the content of your template, hence, once you understand Jaydoh's Template Mechanism, you can use it for any kind of text-based content. For example, you can use Jaydoh's Template Mechanism for WML(WAP).

• To totally separate presentation from business logic.


• To easily combine a number of atomic components in a variety of ways.


• The template mechanism enables Rapid Prototyping. It allows the application interface to be completely built and have things become "dynamic" when they are ready.


• Its inheritance/region based implementation allows you to do things such as swap the look-and-feel depending on the device or user setting. For example, if the user is in a certain age range you can have a look-and-feel that targets that age-group.


• The template mechanism enables reuse of components: you can have the same Object Providers render content to different Templates -- that is, the same business object can be used when a browser connects to the service, in which case you stream back HTML, or when a WAP phone connects to the service, in which case you stream back WML.


• To enable a fast, iterative approach to application development. That is, Graphics Designers and Developers can work in parallel and integrate seamlessly and continuously.


• Let Graphics Designers work with the tools that they already understand and our productive with, such as Macromedia's^TM Dreamweaver. Jaydoh, even has a productivity aid that makes business objects look like library objects in Dreamweaver. Similarly, let Developers work with their favorite tools.


• It's debugger agnostic - meaning any standard debugger can debug all logic, line to line.

• Any content type that is "text" based, such as: HTML, JSP, WML, XML/XSLT, VoxML, Java source, etc.

• The template mechanism supports nested templates.


• It supports Placeholder Substitution. Placeholders can be defined within a Template or within Page Provider (e.g. images) and can be substituted later via a lookup into a PropertiesMap. Jaydoh's PropertiesMap object supports the standard Java properties format as well as an XML based format. In addition, Jaydoh's PropertiesMap collection enables properties to reference other properties for their value and support cascading.


• Fully supports JSP markup.

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