軟件畢設(shè) 外文翻譯

1、Strutsan open-source MVC implementationBy Christian Kirkegaard and Anders Moller,BRICS, University of Aarhus, DenmarkThis article introduces Struts, a Model-View-Controller implementation that uses servlets and JavaServer Pages (JSP) technology. Struts can help you control change in your Web project

2、 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.IntroductionKids in grade school put HTML pages on the Internet. However, there is a monumental difference between a grade school page and a prof

3、essionally developed Web site. The page designer (or HTML developer) must understand colors, the customer, product flow, page layout, browser compatibility, image creation, JavaScript, and more. Putting a great looking site together takes a lot of work, and most Java developers are more interested i

4、n 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 large-scale Web application, you understand the term change. Model-View-Controller (MVC) is a design patter

5、n put together to help control change. MVC decouples interface from business logic and data. Struts is an MVC implementation that uses Servlets 2.2 and JSP 1.1 tags, from the J2EE specifications, as part of the implementation. You may never implement a system with Struts, but looking at Struts may g

6、ive you some ideas on your future Servlets and JSP implementations.Model-View-Controller (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 comes to the rescue. MVC helps resolve some of the

7、issues with the single module approach by dividing the problem into three categories: ModelThe model contains the core of the applications functionality. The model encapsulates the state of the application. Sometimes the only functionality it contains is state. It knows nothing about the view or con

8、troller. ViewThe view provides the presentation of the model. 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. ControllerT

9、he controller reacts to the user input. It creates and sets the model. MVC Model 2The 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 chan

10、ges. On the Web, the browser has to re-query 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 gen

11、erate 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 isnt able to have direct involvem

12、ent 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 commonly known as MVC Model 2 or MVC 2. Figure 1. MVC Model 2Struts, an MVC 2 implementationStruts is a set of cooperating classes, ser

13、vlets, 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 2 displays an overview of Struts. Figure 2. Stru

14、ts viewStruts overview l Client browser An HTTP request from the client browser creates an event. The Web container will respond with an HTTP response. l ControllerThe Controller receives the request from the browser, and makes the decision where to send the request. With Struts, the Controller is a

15、 command design pattern implemented as a servlet. The struts-config.xml file configures the Controller. l Business logicThe 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 busin

16、ess logic. l Model stateThe 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 tag

17、s. l ViewThe 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 compared to other frameworks like Velocity. Struts detailsDisplayed in Figure 3 is a stripped-down UML diagram of the org.apache

18、.struts.action package. Figure 6 shows the minimal relationships among ActionServlet (Controller), ActionForm (Form State), and Action (Model Wrapper). Figure 3:the relationship between ActionServlet (Controller)、 ActionForm (Form State) and Action (Model Wrapper)The ActionServlet classDo you rememb

19、er the days of function mappings? You would map some input event to a pointer to a function. If you where slick, you would place the configuration information into a file and load the file at run time. Function pointer arrays were the good old days of structured programming in C. Life is better now

20、that we have Java technology, XML, J2EE, and all that. The Struts Controller is a servlet that maps events (an event generally being an HTTP post) to classes. And guess what - the Controller uses a configuration file so you don_t have to hard-code the values. Life changes, but stays the same. Action

21、Servlet 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 struts-config.xml file configures the Command. During the creation of the Web project, Action and Actio

22、nForm are extended to solve the specific problem space. The file struts-config.xml 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 un

23、derstand, 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 recompile code when making flow changes. Command functionality can be added by extending ActionServlet.The ActionForm

24、 class ActionForm maintains the session state for the Web application. ActionForm is an abstract class that is sub-classed 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

25、have a UserActionForm that is set by an HTML Form. The Struts framework will: Check to see if a UserActionForm exists; 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 request.get

26、Parameter() calls. For instance, the Struts framework will take fname from request stream and call UserActionForm.setFname(). The Struts framework updates the state of the UserActionForm before passing it to the business wrapper UserAction. Before passing it to the Action class, Struts will also con

27、duct form state validation by calling the validation() method on UserActionForm.Note: This is not always wise to do. There might be ways of using UserActionForm in other pages or business objects, where the validation might be different. Validation of the state might be better in the UserAction clas

28、s. The UserActionForm can be maintained at a session level. Notes: The struts-config.xml file controls which HTML form request maps to which ActionForm. Multiple requests can be mapped UserActionForm. UserActionForm can be mapped over multiple pages for things such as wizards. The Action classThe Ac

29、tion class is a wrapper around the business logic. The purpose of Action class is to translate the HttpServletRequest to the business logic. To use Action, subclass and overwrite the process() method. The ActionServlet (Command) passes the parameterized classes to ActionForm using the perform() meth

30、od. Again, no more dreadful request.getParameter() calls. By the time the event gets here, the input form data (or HTML form data) has already been translated out of the request stream and into an ActionForm class. Note: Think thin when extending the Action class. The Action class should control the

31、 flow and not the logic of the application. By placing the business logic in a separate package or EJB, we allow flexibility and reuse.Another way of thinking about Action class is as the Adapter design pattern. The purpose of the Action is to Convert the interface of a class into another interface

32、the clients expect. Adapter lets classes work together that couldn_t otherwise because of incompatibility interface (from Design Patterns - Elements of Reusable OO Software by Gof). The client in this instance is the ActionServlet that knows nothing about our specific business class interface. There

33、fore, Struts provides a business interface it does understand, Action. By extending the Action, we make our business interface compatible with Struts business interface. (An interesting observation is that Action is a class and not an interface. Action started as an interface and changed into a clas

34、s over time. Nothings perfect.) The Error classesThe UML diagram (Figure 4) 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

35、up with a list of errors.Figure 4:the relationship between Command (ActionServlet) and Model (Action)The ActionMapping classAn incoming event is normally in the form of an HTTP request, which the servlet Container turns into an HttpServletRequest. The Controller looks at the incoming event and dispa

36、tches the request to an Action class. The struts-config.xml determines what Action class the Controller calls. The struts-config.xml 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

37、 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.ActionMappingsActionMappings is

38、 a collection of ActionMapping objects.Struts pros Use of JSP tag mechanismThe tag feature promotes reusable code and abstracts Java code from the JSP file. This feature allows nice integration into JSP-based development tools that allow authoring with tags. Tag libraryWhy re-invent the wheel, or a

39、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 sourceYou have all the advantages of open source, such as being able to see the code and having everyone else using the library re

40、viewing the code. Many eyes make for great code review. Sample MVC implementationStruts offers some insight if you want to create your own MVC implementation. Manage the problem spaceDivide and conquer is a nice way of solving the problem and making the problem manageable. Of course, the sword cuts

41、both ways. The problem is more complex and needs more management. Struts cons YouthStruts development is still in preliminary form. They are working toward releasing a version 1.0, but as with any 1.0 version, it does not provide all the bells and whistles. ChangeThe framework is undergoing a rapid

42、amount of change. A great deal of change has occurred between Struts 0.5 and 1.0. 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

43、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 abstractionDoes Struts provide the correct level of abstraction? What is the proper level of abstraction for the page designer? That is the $64K questio

44、n. Should we allow a 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

45、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 wa

46、it for a COM developer to create it when I can program it directly with VBScript? Struts helps limit the amount of Java code required in a JSP file via tag libraries. One such library is the Logic Tag, which manages conditional generation of output, but this does not prevent the UI developer from go

47、ing nuts with Java code. Whatever type of framework you decide to use, you should understand the environment in which you are deploying and maintaining the framework. Of course, this task is easier said than done. Limited scopeStruts is a Web-based MVC solution that is meant be implemented with HTML

48、, JSP files, and servlets. J2EE application supportStruts requires a servlet container that supports JSP 1.1 and Servlet 2.2 specifications. This alone will not solve all your install issues, unless you are using Tomcat 3.2. ComplexitySeparating the problem into parts introduces complexity. There is

49、 no question that some education will have to go on to understand Struts. With the constant changes occurring, this can be frustrating at times. Future of StrutsThings change rapidly in this new age of software development. In less than 5 years, we have seen things go from cgi/perl, to ISAPI/NSAPI,

50、to ASP with VB, and now Java and J2EE. Sun is working hard to adapt changes to the JSP/servlet architecture, just as they have in the past with the Java language and API. You can obtain drafts of the new JSP 1.2 and Servlet 2.3 specifications from the Sun Web site. Additionally, a standard tag libra

51、ry for JSP files is appearing大連交通大學(xué)2013屆本科生畢業(yè)設(shè)計(jì)(論文)外文翻譯中文翻譯StrutsMVC的一種開放源碼實(shí)現(xiàn)作者：Christian Kirkegaard and Anders Moller,BRICS, University of Aarhus, Denmark本文介紹Struts，它是使用 servlet 和 JavaServer Pages 技術(shù)的一種 Model-View-Controller 實(shí)現(xiàn)。Struts 可幫助您控制 Web 項(xiàng)目中的變化并提高專業(yè)化水平。盡管您可能永遠(yuǎn)不會(huì)用 Struts 實(shí)現(xiàn)一個(gè)系統(tǒng)，但您可以將其中的一些思想用

52、于您以后的 servlet 和 JSP 網(wǎng)頁(yè)的實(shí)現(xiàn)中。小學(xué)生也可以在因特網(wǎng)上發(fā)布 HTML 網(wǎng)頁(yè)。但是，小學(xué)生的網(wǎng)頁(yè)和專業(yè)開發(fā)的網(wǎng)站有質(zhì)的區(qū)別。網(wǎng)頁(yè)設(shè)計(jì)人員（或者 HTML 開發(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。設(shè)計(jì)漂亮的網(wǎng)站需要做大量的工作，大多數(shù) Java 開發(fā)人員更注重創(chuàng)建優(yōu)美的對(duì)象接口，而不是用戶界面。JavaServer Pages (JSP) 技術(shù)為網(wǎng)頁(yè)設(shè)計(jì)人員和 Java 開發(fā)人員提供了一種聯(lián)系鈕帶。如果您開發(fā)過(guò)大型 Web 應(yīng)用程序，您就理解 變化 這個(gè)詞的含義?！澳Ｐ?視圖-控制器”(MVC) 就是用來(lái)幫助您控

53、制變化的一種設(shè)計(jì)模式。MVC 減弱了業(yè)務(wù)邏輯接口和數(shù)據(jù)接口之間的耦合。Struts 是一種 MVC 實(shí)現(xiàn)，它將 Servlet 2.2 和 JSP 1.1 標(biāo)記（屬于 J2EE 規(guī)范）用作實(shí)現(xiàn)的一部分。盡管您可能永遠(yuǎn)不會(huì)用 Struts 實(shí)現(xiàn)一個(gè)系統(tǒng)，但了解一下 Struts 或許使您能將其中的一些思想用于您以后的 Servlet 的 JSP 實(shí)現(xiàn)中。模型-視圖-控制器 (MVC)JSP 標(biāo)記只解決了部分問(wèn)題。我們還得處理驗(yàn)證、流程控制和更新應(yīng)用程序的狀態(tài)等問(wèn)題。這正是 MVC 發(fā)揮作用的地方。MVC 通過(guò)將問(wèn)題分為三個(gè)類別來(lái)幫助解決單一模塊方法所遇到的某些問(wèn)題：Model（模型）模型包含應(yīng)用

54、程序的核心功能。模型封裝了應(yīng)用程序的狀態(tài)。有時(shí)它包含的唯一功能就是狀態(tài)。它對(duì)視圖或控制器一無(wú)所知。 View（視圖）視圖提供模型的表示。它是應(yīng)用程序的 外觀。視圖可以訪問(wèn)模型的讀方法，但不能訪問(wèn)寫方法。此外，它對(duì)控制器一無(wú)所知。當(dāng)更改模型時(shí)，視圖應(yīng)得到通知。 Controller（控制器）控制器對(duì)用戶的輸入作出反應(yīng)。它創(chuàng)建并設(shè)置模型。 MVC Model 2Web 向軟件開發(fā)人員提出了一些特有的挑戰(zhàn)，最明顯的就是客戶機(jī)和服務(wù)器的無(wú)狀態(tài)連接。這種無(wú)狀態(tài)行為使得模型很難將更改通知視圖。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。另一個(gè)重大變化是實(shí)現(xiàn)視圖所用的技術(shù)與實(shí)現(xiàn)模

55、型或控制器的技術(shù)不同。當(dāng)然，我們可以使用 Java（或者 PERL、C/C+ 或別的語(yǔ)言）代碼生成 HTML。這種方法有幾個(gè)缺點(diǎn)： Java 程序員應(yīng)該開發(fā)服務(wù)，而不是 HTML。 更改布局時(shí)需要更改代碼。 服務(wù)的用戶應(yīng)該能夠創(chuàng)建網(wǎng)頁(yè)來(lái)滿足它們的特定需要。 網(wǎng)頁(yè)設(shè)計(jì)人員不能直接參與網(wǎng)頁(yè)開發(fā)。 嵌在代碼中的 HTML 很難看。 對(duì)于 Web，需要修改標(biāo)準(zhǔn)的 MVC 形式。圖1顯示了 MVC 的 Web 改寫版，通常也稱為 MVC Model 2 或 MVC 2。圖1. MVC Model 2Struts，MVC 2的一種實(shí)現(xiàn)Struts 是一組相互協(xié)作的類、servlet 和 JSP 標(biāo)記，它們

56、組成一個(gè)可重用的 MVC 2 設(shè)計(jì)。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。圖2顯示了 Struts 的一個(gè)概覽。圖2. Struts 概覽Struts 概覽l Client browser（客戶瀏覽器）來(lái)自客戶瀏覽器的每個(gè) HTTP 請(qǐng)求創(chuàng)建一個(gè)事件。Web 容器將用一個(gè) HTTP 響應(yīng)作出響應(yīng)。l Controller（控制器）控制器接收來(lái)自瀏覽器的請(qǐng)求，并決定將這個(gè)請(qǐng)求發(fā)往何處。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。 struts-config.xml 文件配置控制器

57、。l 業(yè)務(wù)邏輯業(yè)務(wù)邏輯更新模型的狀態(tài)，并幫助控制應(yīng)用程序的流程。就 Struts 而言，這是通過(guò)作為實(shí)際業(yè)務(wù)邏輯“瘦”包裝的 Action 類完成的。l Model（模型）的狀態(tài)模型表示應(yīng)用程序的狀態(tài)。業(yè)務(wù)對(duì)象更新應(yīng)用程序的狀態(tài)。ActionForm bean 在會(huì)話級(jí)或請(qǐng)求級(jí)表示模型的狀態(tài)，而不是在持久級(jí)。JSP 文件使用 JSP 標(biāo)記讀取來(lái)自 ActionForm bean 的信息。l View（視圖）視圖就是一個(gè) JSP 文件。其中沒有流程邏輯，沒有業(yè)務(wù)邏輯，也沒有模型信息 - 只有標(biāo)記。標(biāo)記是使 Struts 有別于其他框架（如 Velocity）的因素之一。詳細(xì)分析 Struts圖3

58、示的是 org.apache.struts.action 包的一個(gè)最簡(jiǎn) UML 圖。圖3顯示了 ActionServlet (Controller)、 ActionForm (Form State) 和 Action (Model Wrapper) 之間的最簡(jiǎn)關(guān)系。圖3. Command (ActionServlet) 與 Model (Action & ActionForm) 之間的關(guān)系的 UML 圖ActionServlet 類 您還記得函數(shù)映射的日子嗎？在那時(shí)，您會(huì)將某些輸入事件映射到一個(gè)函數(shù)指針上。如果您對(duì)此比較熟悉，您會(huì)將配置信息放入一個(gè)文件，并在運(yùn)行時(shí)加載這個(gè)文件。函數(shù)指針數(shù)組曾經(jīng)是用 C 語(yǔ)言進(jìn)行結(jié)構(gòu)化編程的很好方法?，F(xiàn)在好多了，我們有了 Java 技術(shù)、XML、J2EE，等等。Struts 的控制器是將事件（事件通常是 HTTP post）映射到類的一個(gè) servlet。正如您所料 - 控制器使用配置文件以使您不必對(duì)這些值進(jìn)行硬編碼。時(shí)代變了，但方法依舊。ActionServlet 是該 MVC 實(shí)現(xiàn)的 Command 部分