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Model 2X
Model 2X is the result of a natural evolution that started in the early days of Web application development. This architecture enhances Model 2, allowing a more flexible and modular front-end design. With Model 2X, XML is generated by the Servlet or the JSP. This XML goes through a sequence of transformations before being sent to the browser. The sequence of transformations is described in XML pipelines. To better understand the relationship between J2EE technologies such as JSP/JSF and XML pipelines, read the article published recently by Orbeon on TheServerSide.com.
Model 1
Model 1 consists of using JSP to extract data from the HTTP request parameters, call the business logic implemented in JavaBeans or directly into the JSP, handle the HTTP session, and generate the HTML output. Using this approach usually leads to a significant amount of scriptlets (Java code embedded in HTML). Another limitation of Model 1 is that each JSP page must be individually responsible for managing the application state and verifying authentication and security./*
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Model 2
Model 2 is a server-side implementation of the Model View Controller architecture using Servlets and Java Server Pages (JSP). In Model 2, Servlets control the flow of the Web application and delegate the business logic to either JavaBeans or EJBs, while JSP pages take care of producing the HTML. This model encourages a much cleaner separation of business and presentation logic, making application development as well as maintenance a much easier task. The most popular example of frameworks implementing Model 2 is an Apache Jakarta project called Struts.
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Model 2X
Model 2 based frameworks are a big step in the right direction. However, in some cases it is not necessarily optimal to output HTML directly from JSPs to the Web browser. For example, there are situations where it would be desirable to separate look and feel logic from the localization. Likewise, there might be situations where the same application has requirements to support multiple devices with the same back-end logic. These are perfect use cases for an XML/XSLT approach. Executing a series of XML transformations before sending the appropriate markup language to the Web browser is a better approach. That is why Orbeon introduced Model 2X back in February 2002 in an article published in JavaWorld magazine.
