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【正文】 在最近 5 年里 ，我目睹 過(guò)事物 從 cgi/perl ，再 到 ISAPI/NSAPI、再到使用 VB 的 ASP、一直到現(xiàn)在的 Java 和 J2EE 的變遷。僅憑這一點(diǎn)遠(yuǎn)不能解決你的全部安裝問(wèn)題，除非使用 Tomcat 。在 ASP 開(kāi)發(fā)中，你應(yīng)該創(chuàng)建 COM 對(duì)象，然后編寫少量的 ASP 腳本將這些 COM 對(duì)象聯(lián)系起來(lái)。為了避免使用不贊成使用的方法，你可能隔一天就需要下載最新的 Struts。 ? MVC 實(shí)現(xiàn)樣例 如果你希望創(chuàng)建你自己的 MVC 實(shí)現(xiàn)，則 Struts 可增加你的見(jiàn)識(shí)。這樣就使 Action 可訪問(wèn)用于控制流程的信息。 ActionErrors 是 ActionError 類的容器， View 可以使用標(biāo)記訪問(wèn)這些類。本例中的客戶機(jī)是 ActionServlet ，它對(duì)我們的具體業(yè)務(wù)類接口一無(wú)所知。 通過(guò)事件到達(dá)這里的時(shí)間 ，輸入表單數(shù)據(jù)（或 HTML 表單數(shù)據(jù)） 已經(jīng) 被從請(qǐng)求流中 翻譯 出來(lái)并 進(jìn)入 ActionForm 類中。 備 注 ： ? 文件控制 著 HTML 表單請(qǐng)求與 ActionForm 之間的映射。沒(méi)有太多 糟糕 的 請(qǐng)求 .getParameter() 調(diào)用。 ? 當(dāng)流程發(fā)生改變時(shí) Java 開(kāi)發(fā)人員不需要重新編譯代碼 。 猜猜怎么著 控制器用 一個(gè) 配置文件以 致于 你不必 非 硬編碼這些值。 Struts 詳細(xì)資料 在圖 6 中展示了一個(gè)無(wú)其他附屬設(shè)備的阿帕奇 struts 的 action 包的 UML 圖表 。就 Struts 而言，這 就 是通過(guò)作為實(shí)際業(yè)務(wù)邏輯 “瘦 ”包裝的 Action 類完成的。這個(gè)定義表示 Struts 是一個(gè)框架，而不是一個(gè)庫(kù)，但 Struts 也包含了豐富的標(biāo)記庫(kù)和獨(dú)立于該框架工作的實(shí)用程序類。 這種方法存在一些弊端 ： ? Java 程序員應(yīng)該開(kāi)發(fā)服務(wù)，而不是 HTML。視圖僅僅當(dāng)模型發(fā)生改變的時(shí)候才被通知 。 MVC 通過(guò)把問(wèn)題分成三類來(lái)幫助解決一些與單模塊相關(guān)的問(wèn)題 ： ? Model（模型） 模塊包括應(yīng)用程序功能的核心。 如果你開(kāi)發(fā)過(guò)大型 Web 應(yīng)用程序，你就理解“變化”這個(gè)詞語(yǔ)。s perfect.) The Error classes The UML diagram (Figure 6) also included ActionError and ActionErrors. ActionError encapsulates an individual error message. ActionErrors is a container of ActionError classes that the View can access using tags. ActionErrors is Struts way of keeping up with a list of errors. Figure 7. UML diagram of the relationship of the Command (ActionServlet) to the 第 8頁(yè) 共 20頁(yè) Model (Action) The ActionMapping class An ining event is normally in the form of an HTTP request, which the servlet Container turns into an HttpServletRequest. The Controller looks at the ining event and dispatches the request to an Action class. The determines what Action class the Controller calls. The configuration information is translated into a set of ActionMapping, which are put into container of ActionMappings. (If you have not noticed it, classes that end with s are containers) The ActionMapping contains the knowledge of how a specific event maps to specific Actions. The ActionServlet (Command) passes the ActionMapping to the Action class via the perform() method. This allows Action to access the information to control flow. ActionMappings ActionMappings is a collection of ActionMapping objects. Struts pros ? Use of JSP tag mechanism The tag feature promotes reusable code and abstracts Java code from the JSP file. This feature allows nice integration into JSPbased development tools that allow authoring with tags. 第 9頁(yè) 共 20頁(yè) ? Tag library Why reinvent the wheel, or a tag library? If you cannot find something you need in the library, contribute. In addition, Struts provides a starting point if you are learning JSP tag technology. ? Open source You have all the advantages of open source, such as being able to see the code and having everyone else using the library reviewing the code. Many eyes make for great code review. ? Sample MVC implementation Struts offers some insight if you want to create your own MVC implementation. ? Manage the problem space Divide and conquer is a nice way of solving the problem and making the problem manageable. Of course, the sword cuts both ways. The problem is more plex and needs more management. Struts cons ? Youth Struts development is still in preliminary form. They are working toward releasing a version , but as with any version, it does not provide all the bells and whistles. ? Change The framework is undergoing a rapid amount of change. A great deal of change has occurred between Struts and . You may want to download the most current Struts nightly distributions, to avoid deprecated methods. In the last 6 months, I have seen the Struts library grow from 90K to over 270K. I had to modify my examples several times because of changes in Struts, and I am not going to guarantee my examples will work with the version of Struts you download. ? Correct level of abstraction Does Struts provide the correct level of abstraction? What is the proper level of abstraction for the page designer? That is the $64K question. Should we allow a 第 10頁(yè) 共 20頁(yè) page designer access to Java code in page development? Some frameworks like Velocity say no, and provide yet another language to learn for Web development. There is some validity to limiting Java code access in UI development. Most importantly, give a page designer a little bit of Java, and he will use a lot of Java. I saw this happen all the time in Microsoft ASP development. In ASP development, you were supposed to create COM objects and then write a little ASP script to glue it all together. Instead, the ASP developers would go crazy with ASP script. I would hear Why wait for a COM developer to create it when I can program it directly with VBScript? Struts helps limit
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