JavaServer Page

Tag-based programming

Separating these two layers is a problem in the other extension mechanisms we ve mentioned, but the page-centric nature associated with server pages applications makes the problem much more pronounced. Whereas a CGI developer can come up with his or her own page-generation template system to separate presentation and business logic, server pages technologies dictate a specific template system into which the developer is locked. In addition, the powerful scripting language that can be used within the pages makes it possible to implement quick and dirty applications that place the majority of the business logic directly inside the server page. The result is that many server pages-based applications lack an adequate separation of layers. 1.4 Tag-based programming Thus far we ve covered a number of different approaches to dynamic web development. We ve seen how CGI scripts allow the building of dynamic sites, but suffer from some significant performance problems. We ve seen how server API solutions may overcome CGI s speed issues, but add a lot of complexity to development and tie you very closely to a particular server vendor. We ve looked at server page approaches which are acceptably quick at execution time and much easier to implement than API solutions, but encourage poor separation between presentation and business logic layers. What is the next step in the evolution of dynamic web development? It is none other than the subject of this book: tag-based development. JSP custom tags are not the first tag-based approach. ColdFusion, a product from Allaire Corp., is a well-known implementation of this tag-based concept and was introduced before custom JSP tags. ColdFusion still enjoys a solid market share for web development, but is less attractive to many developers because it is a proprietary solution while custom tags are defined in the open JSP specification. Being a purely Java solution, custom tags also enjoy all the normal benefits such as being cross platform, widely supported, and written in a fully functional language. Cold- Fusion does not boast this same cross platform ability, nor is it an open standard that is available to multiple vendors. As we ll see in future chapters, engines that run custom JSP tags within a web server can be built by any company willing to adhere to certain open standards. At least a dozen vendors have built these solutions today, Allaire being one of them.

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