外文翻譯中小型企業(yè)員工工作信息管理系統(tǒng)-文庫(kù)吧資料
2024-11-21 11:54本頁面
【正文】 update itself. This approach lets you attach multiple views to a Luo Guangchun the . of UEST of China Wang Yanhua the Master of the UEST of China Lu Xianliang theprofessor of UEST of China advisor of . Han Hong the . of UEST Of Chinamodel to provide different presentations. You can also create new views for a modelwithout rewriting . Background and Problems Even though the MVC design pattern was already put forward in smalltalk80 andwidely used in software design it is difficult to introduce it into the Web applicationdevelopment. It was mainly due to the following two factors: 1 First it was difficult toseparate the programming language from HTML. Early CGI programs created the HTMLcontent by using character string output. In nature it divided the HTML content intoseveral portions and then inserted them into the CGI programs. After the appearance ofScript languages the way changed to insert the programs written by script languages intoHTML content. However these two ways had a mon deficiency that they could notseparate the programs from the HTML content absolutely. Therefore it is very difficult toimplement the MVC detached threelayer pattern based on these two ways. 2 Secondfunctions of the script languages are less weak. They lack some necessary technologies tosupport the MVC design pattern such as message mechanism and event responsemechanism. This situation did not get any improvement until the release of the JSP Model24. Depending on the powerful functions of Java language the JSP Model 2 implementsthe MVC design idea to some extent. Figure 1 shows the mechanism: Model the data layer: it is encapsulated into the Enterprise JavaBean. View the presentation layer: JSP is responsible for the presentation of pages such as the presentation format paging etc. Controller the control layer: Servlet receives the user input in pages and executes the relevant transaction calling the corresponding EJB modules then gives theresults to the relevant View so JSP can present these results. This mechanism of JSP Model 2 basically meets the developers’ requirements todetach the Web application transaction logic from the user interface. But some limits stillexist. For example although JSP Model 2 has implemented the basic idea of the MVCdesign pattern the relationship of these three layers Serv
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