【正文】 del. It is the look of the application. The view can access the model getters, but it has no knowledge of the setters. In addition, it knows nothing about the controller. The view should be notified when changes to the model occur. ? Controller The controller reacts to the user input. It creates and sets the model. 3 MVC Model 2 The Web brought some unique challenges to software developers, most notably the stateless connection between the client and the server. This stateless behavior made it difficult for the model to notify the view of changes. On the Web, the browser has to requery the server to discover modification to the state of the application. Another noticeable change is that the view uses different technology for implementation than the model or controller. Of course, we could use Java (or PERL, C/C++ or what ever) code to generate HTML. There are several disadvantages to that approach: ? Java programmers should develop services, not HTML. ? Changes to layout would require changes to code. ? Customers of the service should be able to create pages to meet their specific needs. ? The page designer isn39。 MVC。 外 文 翻 譯 英文題目： Infrastructure for Automatic Dynamic Deployment Of J2EE Application in Distributed Environments amp。 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)的自動動態(tài)配置的應(yīng)用 與 Struts—— MVC 的一種開放源碼實現(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。 JSP 1 Introduction Kids in grade school put HTML pages on the Inter. However, there is a monumental difference between a grade school page and a professionally developed Web site. The page designer (or HTML developer) must understand colors, the customer, product flow, page layout, browser patibility, image creation, JavaScript, and more. Putting a great looking site together takes a lot of work, and most Java developers are more interested in creating a great looking object interface than a user interface. JavaServer Pages (JSP) technology provides the glue between the page designer and the Java developer. If you have worked on a largescale Web application, you understand the term change. ModelViewController (MVC) is a design pattern put together to help control change. MVC decouples interface from business logic and data. Struts is an MVC implementation that uses Servlets and JSP tags, from the J2EE specifications, as part of the implementation. You may never implement a system with Struts, but looking at Struts may give you some ideas on your future Servlets and JSP implementations. 2 ModelViewController (MVC) JSP tags solved only part of our problem. We still have issues with validation, flow control, and updating the state of the application. This is where MVC es to the rescue. MVC helps resolve some of the issues with the single module approach by dividing the problem into three categories: ? Model The model contains the core of the application39。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。 if not, it will create an instance of the class. ? Struts will set the state of the UserActionForm using corresponding fields from the HttpServletRequest. No more dreadful () calls.