My space web page - CHAPTER 11 ADVANCED FILTERING TECHNIQUES 451 Filter
CHAPTER 11 ADVANCED FILTERING TECHNIQUES 451 Filter 3: A Filter for Adapting to Legacy Resources The next filter you will examine addresses a common problem in the real world that occurs when two independent systems refer to each other through hyperlinks. Over time, the requirement and access changes because of independent evolution. Imagine that because of the size of the independent projects, or because of political situations, you can t change the links to either one of the systems. To keep them working, you ll create a filter that adapts one system to another, without modifying a single line of code in either system. Figure 11-10 shows the action of just such an adapter filter within a typical system. Figure 11-10. Filters can modify requests so that two systems that were not built to work together can be integrated. In this example, a JSP page represents the legacy resource. A centralized administrative server that is accessed by multiple departments in a company services this JSP page. This legacy system requires the originating department information to be supplied in the form of a DEPT parameter in order to work properly. Unfortunately, because of political situations in this hypothetical company, the links coming into this server don t and won t contain the originating department information (the DEPT parameter). Therefore, you ll design a filter to adapt
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