well-intentioned friends and experts, is not to use scriptlets. Instead, they tell the new JSP programmer to use custom tags. Custom tags are a means by which the JSP platform's capabilities are extended: custom XML-style tags, tied to code libraries, implement the desired functionality. We'll see how well they work, in our next example.
The Jakarta TagLibs Project is a subproject of the Jakarta Project, the official reference implementation of the Java Servlet and JavaServer Pages technologies.
ATSC制数字电视机顶盒研究One of the packages developed under the auspices of the Jakarta TagLibs Project is the DBTags custom tag library (formerly known as the JDBC tag library). The JSP page in Listing 4 implements the same hit counter as in Listing 3, replacing the scriptlet with custom tags.
Most tag libraries written to date have been written by programmers for programmers; the semantics of those tags are geared toward other programmers. Furthermore, remember the separation of model and presentation? That isn't well supported by DBTags. The sql:getColumn tag is analogous to the jsp:getProperty action: it emits the tag's result directly into the output stream. That makes it difficult to separate using DBTags from rendering output into the desired form. Finally, notice that the logic differs between Listing 3 and Listing 4. The DBTags execute tag consumes the update count from any 本文来自优.文,论^文·网原文请找腾讯752018766 , it is not a bad tag library for programmers. Aside from its consumption of the update count, the code provides a fairly good mapping to JDBC. Therein lies the problem, however: the tags provide little more than a direct translation of the JDBC package. Other than hiding some exception handling, the tag library doesn't really provide any abstraction over scriptlets. It certainly doesn't help separate presentation from function.
So, the real issue is not whether to use scriptlets or tags; that question is a consequence, not a cause, of the problem of separating function from presentation
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