Struts开源框架中英文对照外文翻译文献

中英文对照外文翻译文献(文档含英文原文和中文翻译)Best practices for Struts developmentStruts: A brief introductionStruts, an open source framework you can use to build Web applications, is based on the popular Model-View-Controller (MVC2) design paradigm. The framework is built upon standard technologies like Java Servlets, JavaBeans, ResourceBundles, and XML, and it provides flexible and extensiblecomponents. Struts implements the Controller layer in the form of ActionServlet and recommends building the View layer using JSP tag libraries. Struts also provides a wrapper around theModel layer through Action classes. Figure 1 illustrates the Struts framework based on theModel-View-Controller design.Figure 1. Struts and MVCOverview of Struts componentsFirst, we'll explain the Struts components in the context of best practices and the role each one plays in your Web application development.ActionEvery Action of your application extendsStruts' org.apache.struts.action.Action. These Action classes provide an interface to the application's Model layer, acting as a wrapper around the business logic.Each Action class must provide its case-specific implementation to the perform() method. The perform() method always returns a value of type ActionForward. ActionFormEvery ActionForm of your application extendsStruts' org.apache.struts.action.ActionForm. ActionForm s are simple JavaBeans that encapsulate and validate request parameters. To validate your request data, your ActionForm's validate() method must give a case-specific implementation. ActionForm s serve as a carrier of request data to the Action class. A JSP object combines with a respective ActionForm to form your application's View layer, where almost every form field of the JSP object maps to an attribute of the corresponding ActionForm. JSP custom tag librariesThe JSP custom tag libraries are a collection of actions presented as tags. This is a powerful feature of the JSP Specification 1.1; it allows you to separate presentation from other application tiers. The libraries are easy to use and you can read them in XML-like fashion. You can easily maintain the JSP components by minimizing the use of Java scriptlets in them. The JSP tags that Struts provides include HTML, logic, and bean tags.ActionErrorsYou use ActionError s to support exception handling. An ActionError traps and propagates an application exception to the View layer. Each one is a collectionof ActionError instances. ActionError s encapsulate error messages, whilethe </html:errors> in the Presentation layer renders all error messages inthe ActionError collection.Best Practice 1. Reuse data across multiple ActionFormsNow that you are familiar with the Struts components, we will continue by showing you ways to get the most out of the framework. First, Struts recommends that you associate every JSP object withan ActionForm, which encapsulates data represented in the screen. You access the form data in the JSP object using accessory methods found in ActionForm. Listing 1 shows the conventional use of ActionForm tag in the View layer.Listing 1. Using ActionForm in JSP<html:form action="/bp1"><html:text property="attrib1" /></html:form >The ActionForm called "BP1AForm" includes the attribute attrib1, as well as its getter and setter methods. In the configuration file struts-config.xml, the action "/bp1" maps to bp1AForm using the name attribute. This facilitates data display in the JSP.To implement this best practice, Struts recommends you do two things:1. Create a JavaBean (BP1BForm) with attributes that form an attribute subsetin BP1AForm, along with the attributes' getter and setter methods.2. Replace the attributes in BP1AForm with the bean BP1BForm by associating the beanwith BP1AForm. Now you can access this attribute subsetin BP1AForm through BP1BForm. Listing 2 shows you how.Listing 2. Accessing form attributes in JSP<html:form action="/bp1"><bean:define name="bp1AForm" property="bp1BForm" id="bp1B"type="com.ibm.dw.webarch.struts.BP1BForm" /><html:text name="bp1B" property="subsetAtt1" /></html:form >Best Practice 2. Use Action class to handle requestsTypically when using the Struts framework, for every action the JSP component requests your application to execute, the application must extendStruts' org.apache.struts.action.Action to create an Action class. This individual Action class interfaces with the application's Model layer while processing the request.To implement this practice, Struts recommends you follow these steps:1. Create an Action class, say BP2Action, byextending org.apache.struts.action.Action.2. Create all other Action classes in your Web application by extending BP2Action.3. In BP2Action, create a method performTask(), as in publicabstract ActionForward performTask(ActionMappingmapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws IOException,ServletException.4. In BP2Action add one or more generic methods to the application, forexample serverSideValidate(). You can decide on the method's accessmodifier by considering the following factors:o If all Action classes must implement this method, make it abstract.o If some Action classes will provide a case-specific implementation, declare the method protected and give it a default implementation.5. In BP2Action, declare method perform() as final. Invoke the above genericmethod, which must always be called before processing the request. Now call themethod performTask() created in step 3.6. In every Action class extending BP2Action, addmethod performTask() with a case-specific implementation.AdvantagesThis practice has two main advantages. First, it helps you avoid redundant code inevery Action class of your Web application. Second, it gives the application more control over generic tasks by centralizing the behavior in one Action class.Best Practice 3. Use ActionForm to work on session dataIn a Struts-based Web application,each ActionForm extends org.apache.struts.action.ActionForm. These ActionForm s encapsulate page data and provide a validation framework to validate request parameters.Most Web applications maintain data in session to make them available throughout the application. This best practice addresses this Web application feature. It allowsmethods toSession() and fromSession() to move session data to and from the form data. Thus, it addresses session data maintenance in a Web application.To adhere to this practice, follow these steps:1. Create an abstract class named BP3Form byextending org.apache.struts.action.ActionForm.2. In BP3Form, add methods with access modifiers as in public abstract voidtoSession(SessionData sessionData) and voidfromSession(SessionData sessionData).3. In every ActionForm, extend BP3Form and implement the abstract methods inwhich the form data is transported to and from the session.4. The corresponding Action class may determine the order in which these methods arecalled. For example, you could invoke method toSession() onthe ActionForm just before actionForward is determined.When to use this practiceThis practice is most useful when session data is maintained as a single object and/or every page manipulates or uses session data.Best Practice 4. Handle exceptions effectivelyConventionally, when an application exception occurs in an Action class, the exception is first logged. Then the class creates an ActionError and stores it in the appropriate scope.This Action class then forwards control to the appropriate ActionForward. Listing 3 shows how Action class handles exceptions.Listing 3. Exception handling in an Action classtry {//Code in Action class}catch (ApplicationException e) {//log exceptionActionErrors actionErrors = new ActionErrors();ActionError actionError = new ActionError(e.getErrorCode());actionErrors.add(ActionErrors.GLOBAL_ERROR, actionError);saveErrors(request, actionErrors);}While conventional exception handling procedures save exception information inevery Action class, best practice 4 aims to avoid redundant code while handling exceptions.To use this practice, Struts recommends following these steps:1. Create an Action class, say BP4Action, byextending org.apache.struts.action.Action.2. Create all other Action classes in your Web application by extending BP4Action.3. In BP4Action, declare variable ActionErrors actionErrors = newActionErrors();.4. In BP4Action, create a method performTask() as in publicabstract ActionForward performTask(ActionMappingmapping, ActionForm form, HttpServletRequest request, HttpServletResponse response, ActionErrorsactionErrors) throws IOException, ServletException.5. In BP4Action, declare method perform() as final. Then invoke generic methods,which must always be called before processing the request. Now you can call themethod performTask() created in the previous step.6. While implementing method performTask() in every Action class (byextending BP4Action), handle application exceptions as shown in Listing 4.Listing 4. Using ActionErrors effectivelytry {//Code in Action class}catch(ApplicationException appException) {//Log exception//Add error to actionErrorsactionErrors.add(ActionErrors.GLOBAL_ERROR,new ActionError(appException.getErrorCode()));}In BP4Action, after invoking the method performTask(), savethe ActionErrors using saveErrors(request, errors).AdvantagesThis practice's main advantage is that it avoids code redundancy in every Action class that handles ActionErrors.In conclusionBuilding an easily maintainable Web application can be one of the most challenging tasks for a development team. Using a mature framework like Struts helps you implement the infrastructure code normally associated with building an application. The Struts framework provides a set of standard interfaces for plugging business logic into the application, a consistent mechanism across development teams for performing tasks such as user data validation, screen navigation, and so forth, as well as aset of custom tag libraries to simplify developing screens.These four best practices are important for you to extract more from the framework's features. You, asa developer, can benefit from these lessons to increase your code modularity and application reusability, plus minimize code redundancy. These are all critical to building an extensible Web application.译文:Struts 开发的最佳实践Struts：简介Struts 是一种开源框架，可用来构建 Web 应用程序，它基于流行的Model-View-Controller (MVC2) 设计范型。