JSP model 2 architecture

JSP Model 2 is a complex

to encapsulate the MVC Model.

In a Model 2 application, requests from the

) and decides which view it will pass the request to. The view then renders the content passed by the controller.

Model 2 is recommended for medium- and large-sized applications.

History

In 1998, Sun Microsystems published a pre-release of the

" due to its ordering in the document) was a simplistic model whereby JSP pages were standalone, disjointed entities. Logic could be contained within the page itself, and navigation between pages was typically achieved by way of hyperlinks. This fit with the then-common usage of template technology.

are examples of contemporary technologies that also implemented this model.

The second model referred to by the document ("model 2" in the ordering) was an improved method that combined

servlet

technology with JSP technology. The specific difference listed was that a servlet would intercept the request, place the content to render into a request attribute (typically represented by a JavaBean), then call a JSP to render the content in the desired output format. This model differed from the previous model in the fact that JSP technology was used as a pure template engine. All of the logic was separated out into a servlet, leaving the JSP with the sole responsibility of rendering the output for the content provided.

In December 1999, JavaWorld published an article by Govind Seshadri entitled Understanding JavaServer Pages Model 2 architecture.[2] In this article, Govind accomplished two major milestones in the use of the term "Model 2". The first milestone was to formalize the term "Model 2" as an architectural pattern rather than one of two possible options. The second milestone was the claim that Model 2 provided an MVC architecture for web-based software.^[3]

Govind believed that because "Model 2" architecture separated the logic out of the JSP and placed it in a servlet, the two pieces could be seen as the "View" and the "Controller" (respectively) in an MVC architecture. The "Model" part of the MVC architecture was left open by Govind, with a suggestion that nearly any data-structure could meet the requirements. The specific example used in the article was a

list stored in the user's session.

In March 2000, the

Since the release of Struts, a number of competing frameworks have appeared. Many of these frameworks also claim to implement "Model 2" and "MVC". In result, the two terms have become synonymous in the minds of developers. This has led to the use of the term "MVC Model 2" or "MVC2" for short.

Misconceptions

A common misconception is that a formalized MVC pattern is required to achieve a Model 2 implementation. However, the Java BluePrints specifically warn against this interpretation:[5]

The literature on Web-tier technology in the J2EE platform frequently uses the terms "Model 1" and "Model 2" without explanation. This terminology stems from early drafts of the JSP specification, which described two basic usage patterns for JSP pages. While the terms have disappeared from the specification document, they remain in common use. Model 1 and Model 2 simply refer to the absence or presence (respectively) of a controller servlet that dispatches requests from the client tier and selects views.

Furthermore, the term "MVC2" has led many to a mistaken belief that Model 2 represents a next-generation MVC pattern. In fact, MVC2 is simply a shortening of the term "MVC Model 2".^[6]

The confusion over the term "MVC2" has led to additional confusion over Model 1 code, resulting in common usage of the nonexistent term "MVC1".

See also

• Apache Struts
  is an open-source framework for implementing web-applications based on a Model 2 architecture.

References

External links

• Seshadri, Govind (December 29, 1999). "Understanding JavaServer Pages Model 2 architecture".
  JavaWorld
  . Retrieved 2020-07-17.
• A History of MVC, Including Model 2
• ASP.NET Presentation Patterns - In this article Dino Esposito discusses how Model2 is also used in ASP.NET MVC.