【正文】 de the values. Life changes, but stays the same. ActionServlet is the Command part of the MVC implementation and is the core of the Framework. ActionServlet (Command) creates and uses Action, an ActionForm, and ActionForward. As mentioned earlier, the file configures the Command. During the creation of the Web project, Action and ActionForm are extended to solve the specific problem space. The file instructs ActionServlet on how to use the extended classes. There are several advantages to this approach: ? The entire logical flow of the application is in a hierarchical text file. This makes it easier to view and understand, especially with large applications. ? The page designer does not have to wade through Java code to understand the flow of the application. ? The Java developer does not need to repile code when making flow changes. Command functionality can be added by extending ActionServlet. （ 2） The ActionForm class ActionForm maintains the session state for the Web application. ActionForm is an abstract class that is subclassed for each input form model. When I say input form model, I am saying ActionForm represents a general concept of data that is set or updated by a HTML form. For instance, you may have a UserActionForm that is set by an HTML Form. The Struts framework will: ? Check to see if a UserActionForm exists。 MVC。 Struts—— an opensource MVC implementation 中文 題目 ： 基于 J2EE 在分布式環(huán)境下的底層結(jié)構(gòu)的自動(dòng)動(dòng)態(tài)配置的應(yīng)用 與 Struts—— MVC 的一種開(kāi)放源碼實(shí)現(xiàn) 外文原文 1 Struts—— an opensource MVC implementation Abstract: This article introduces Struts, a ModelViewController implementation that uses servlets and JavaServer Pages (JSP) technology. Struts can help you control change in your Web project and promote specialization. Even if you never implement a system with Struts, you may get some ideas for your future servlets and JSP page implementation. Keywords: Struts。t able to have direct involvement in page development. ? HTML embedded into code is ugly. For the Web, the classical form of MVC needed to change. Figure 1 displays the Web adaptation of MVC, also monly known as MVC Model 2 or MVC 2. Figure 1. MVC Model 2 4 struts overview Struts is a set of cooperating classes, servlets, and JSP tags that make up a reusable MVC 2 design. This definition implies that Struts is a framework, rather than a library, but Struts also contains an extensive tag library and utility classes that work independently of the framework. Figure 3 displays an overview of Struts. Struts overview ： ? Client browser An HTTP request from the client browser creates an event. The Web container will respond with an HTTP response. ? Controller The Controller receives the request from the browser, and makes the decision where to send the request. With Struts, the Controller is a mand design pattern implemented as a servlet. The file configures the Controller. ? Business logic The business logic updates the state of the model and helps control the flow of the application. With Struts this is done with an Action class as a thin wrapper to the actual business logic. ? Model state The model represents the state of the application. The business objects update the application state. ActionForm bean represents the Model state at a session or request level, and not at a persistent level. The JSP file reads information from the ActionForm bean using JSP tags. ? View The view is simply a JSP file. There is no flow logic, no business logic, and no model information just tags. Tags are one of the things that make Struts unique pared to other frameworks like Velocity. Figure 2. Struts overview Note: Think thin when extending the Action class. The Action class should control the flow and not the logic of the application. By placing the business logic in a separate package or EJB, we allow flexibility and reuse. 5 Struts details Displayed in Figure 3 is a strippeddown UML diagram of the package. Figure 1 shows the minimal relationships among ActionServlet (Controller), ActionForm (Form State), and Action (Model Wrapper). Figure 3. UML diagram of the relationship of the Command (ActionServlet) to the Model (Action amp。 Struts 可幫助您控制 Web 項(xiàng)目中的變化并提高專業(yè)化水平。網(wǎng)頁(yè)設(shè)計(jì)人員（或者 HTML 開(kāi)發(fā)人員）必須理解顏色、用戶、生產(chǎn)流程、網(wǎng)頁(yè)布局、瀏覽器兼容性、圖像創(chuàng)建和 JavaScript 等等。 ―模型 視圖 控制器 ‖(MVC) 就是用來(lái)幫助您控制變化的一種設(shè)計(jì)模式。 2 模型 視圖 控制器 (MVC) JSP 標(biāo)記只解決了部分問(wèn)題。模型封裝了應(yīng)用程序 的狀態(tài)。它是應(yīng)用程序的 外觀 。 ? Controller（控制器） ： 控制器對(duì)用戶的輸入作出反應(yīng)。在 Web 上，為了發(fā)現(xiàn)對(duì)應(yīng)用程序狀態(tài)的修改，瀏覽器必須重新查詢服務(wù)器。 ? 更改布局時(shí)需要更改代碼。 對(duì)于 Web，需要修改標(biāo)準(zhǔn)的 MVC 形式。圖 5 顯示了 Struts 的一個(gè)概覽。就 Struts 而言，控制器是以 servlet 實(shí)現(xiàn)的一個(gè)命令設(shè)計(jì)模式。 ? Model（模型）的狀態(tài) 模型表示應(yīng)用程序的狀態(tài)。 ? View（視圖） 視圖就是一個(gè) JSP 文件。圖 6 顯示了 ActionServlet (Controller)、 ActionForm (Form State) 和 Action (Model Wrapper) 之間的最簡(jiǎn)關(guān)系。 現(xiàn)在好多了，我們有了 Java 技術(shù)、 XML、 J2EE，等等。 ActionServlet 是該 MVC 實(shí)現(xiàn)的 Command 部分，它是這一框架的核心。文件 指示 ActionServlet 如何使用這些擴(kuò)展的類。 ? Java 開(kāi)發(fā)人員也不必在更改流程以后重新編譯代碼。當(dāng)我說(shuō) 輸入表單模型 時(shí) ,是指 ActionForm 表示的是由 HTML 表單設(shè)置或更新的一般意義上的數(shù)據(jù)。沒(méi)有太多討厭 的 () 調(diào)用。 注： 這并不總是明智之舉。 注： ? 文件控制 HTML 表單請(qǐng)求與 ActionForm 之間的映射關(guān)系。 Action 類的用途是將 HttpServletRequest 轉(zhuǎn)換為業(yè)務(wù)邏輯。當(dāng)事件進(jìn)展到這一步時(shí)，輸入表單數(shù)據(jù)（或 HTML 表單數(shù)據(jù)）已被從請(qǐng)求流中提取出來(lái)并轉(zhuǎn)移到 ActionForm 類中。 考慮 Action 類的另一種方式是 Adapter 設(shè)計(jì)模式。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。 Action 開(kāi)始為一個(gè)接口，后來(lái)卻變成了一個(gè)類。 ActionErrors 是 ActionError 類的容器， View 可以使用標(biāo)記訪問(wèn)這些類。 確定 Controller 調(diào)用哪個(gè) Action 類。這樣就使 Action 可訪問(wèn)用于控制流程的信息。 ? 標(biāo)記庫(kù) 為什么要另發(fā)明一種輪子，或標(biāo)記庫(kù)呢？如果您在庫(kù)中找不到您所要的標(biāo)記，那就自己定義吧。 ? MVC 實(shí)現(xiàn)樣例 如果您希望創(chuàng)建您自己的 MVC 實(shí)現(xiàn)，則 Struts 可增加您的見(jiàn)識(shí)。 2） Struts 的缺點(diǎn) ? 仍處于發(fā)展初期 Struts 開(kāi)發(fā)仍處于初級(jí)階段。為了避免使用不贊成使用的方法，您可能隔一天就需要下載最新的 Struts。在開(kāi)發(fā)網(wǎng)頁(yè)的過(guò)程中，我們是否應(yīng)該讓網(wǎng)頁(yè)設(shè)計(jì)人員訪問(wèn) Java 代碼？某些框架（如 Velocity）說(shuō)不應(yīng)該，但它提供了另一種 Web 開(kāi)發(fā)語(yǔ)言讓我們學(xué)習(xí)。在 ASP 開(kāi)發(fā)中，您應(yīng)該創(chuàng)建 COM 對(duì)象，然后編寫(xiě)少量的 ASP 腳本將這些 COM 對(duì)象聯(lián)系起來(lái)。無(wú)論您決定使用哪種類型的框架，您都應(yīng)該了解您要在其中部署和維護(hù)該框架的環(huán)境。僅憑