软件毕设 外文翻译
Struts——an open-source MVC implementation
By Christian Kirkegaard and Anders Moller,BRICS, University of Aarhus, Denmark
This 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 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.
Introduction
Kids in grade school put HTML pages on the Internet. 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 compatibility, 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 large-scale Web application, you understand the term change. Model-View-Controller (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 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 give 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 issues with the single module approach by dividing the problem into three categories:
?Model
The model contains the core of the application's functionality. The model encapsulates the state of the application. Sometimes the only functionality it contains is state. It knows nothing about the view or controller.
?View
The 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.
?Controller
The controller reacts to the user input. It creates and sets the model.
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 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 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 isn'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 commonly known as MVC Model 2 or MVC 2.
Figure 1. MVC Model 2
Struts, an MVC 2 implementation
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 2 displays an overview of Struts.
Figure 2. Struts view
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 command design pattern implemented as a servlet. The struts-config.xml 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 compared to other frameworks like Velocity.
Struts details
Displayed in Figure 3 is a stripped-down UML diagram of the org.apache.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 class
Do you remember 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 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.
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 struts-config.xml file configures the Command. During the creation of the Web project, Action and ActionForm 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 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 recompile code when making flow changes. Command functionality can be added by extending ActionServlet.
The ActionForm 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 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.getParameter() 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 conduct 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 class.
?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 class
The Action 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() method. 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 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 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. Therefore, 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 class over time. Nothing's perfect.)
The Error classes
The 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 up with a list of errors.
Figure 4:the relationship between Command (ActionServlet) and Model (Action)
The ActionMapping class
An 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 dispatches 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 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 JSP-based development tools that allow authoring with tags.
?Tag library
Why re-invent 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 complex and needs more management.
Struts cons
?Youth
Struts 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.
?Change
The framework is undergoing a rapid 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 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 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 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 going 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 scope
Struts is a Web-based MVC solution that is meant be implemented with HTML, JSP files, and servlets.
?J2EE application support
Struts 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.
Complexity
Separating the problem into parts introduces complexity. There is 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 Struts
Things 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, 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 library for JSP files is appearing
中文翻译
Struts——MVC的一种开放源码实现
作者：Christian Kirkegaard and Anders Moller,BRICS, University of Aarhus, Denmark 本文介绍Struts，它是使用servlet 和JavaServer Pages 技术的一种Model-View-Controller 实现。Struts 可帮助您控制Web 项目中的变化并提高专业化水平。尽管您可能永远不会用Struts 实现一个系统，但您可以将其中的一些思想用于您以后的servlet 和JSP 网页的实现中。
小学生也可以在因特网上发布HTML 网页。但是，小学生的网页和专业开发的网站有质的区别。网页设计人员（或者HTML 开发人员）必须理解颜色、用户、生产流程、网页布局、浏览器兼容性、图像创建和JavaScript 等等。设计漂亮的网站需要做大量的工作，大多数Java 开发人员更注重创建优美的对象接口，而不是用户界面。JavaServer Pages (JSP) 技术为网页设计人员和Java 开发人员提供了一种联系钮带。
如果您开发过大型Web 应用程序，您就理解变化这个词的含义。“模型-视图-控制器”(MVC) 就是用来帮助您控制变化的一种设计模式。MVC 减弱了业务逻辑接口和数据接口之间的耦合。Struts 是一种MVC 实现，它将Servlet 2.2 和JSP 1.1 标记（属于J2EE 规范）用作实现的一部分。尽管您可能永远不会用Struts 实现一个系统，但了解一下Struts 或许使您能将其中的一些思想用于您以后的Servlet 的JSP 实现中。
模型-视图-控制器 (MVC)
JSP 标记只解决了部分问题。我们还得处理验证、流程控制和更新应用程序的状态等问题。这正是MVC 发挥作用的地方。MVC 通过将问题分为三个类别来帮助解决单一模块方法所遇到的某些问题：
Model（模型）
模型包含应用程序的核心功能。模型封装了应用程序的状态。有时它包含的唯一功能就是状态。它对视图或控制器一无所知。
View（视图）
视图提供模型的表示。它是应用程序的外观。视图可以访问模型的读方法，但不能访问写方法。此外，它对控制器一无所知。当更改模型时，视图应得到通知。
Controller（控制器）
控制器对用户的输入作出反应。它创建并设置模型。
MVC Model 2
Web 向软件开发人员提出了一些特有的挑战，最明显的就是客户机和服务器的无状态连接。这种无状态行为使得模型很难将更改通知视图。在Web 上，为了发现对应用程序状态的修改，浏览器必须重新查询服务器。
另一个重大变化是实现视图所用的技术与实现模型或控制器的技术不同。当然，我们可以使用Java（或者PERL、C/C++ 或别的语言）代码生成HTML。这种方法有几个缺点：
?Java 程序员应该开发服务，而不是HTML。
?更改布局时需要更改代码。
?服务的用户应该能够创建网页来满足它们的特定需要。
?网页设计人员不能直接参与网页开发。
?嵌在代码中的HTML 很难看。
对于Web，需要修改标准的MVC 形式。图1显示了MVC 的Web 改写版，通常也称为MVC Model 2 或MVC 2。
图1. MVC Model 2
Struts，MVC 2的一种实现
Struts 是一组相互协作的类、servlet 和JSP 标记，它们组成一个可重用的MVC 2 设计。这个定义表示Struts 是一个框架，而不是一个库，但Struts 也包含了丰富的标记库和独立于该框架工作的实用程序类。图2显示了Struts 的一个概览。
图2. Struts 概览
Struts 概览
Client browser（客户浏览器）
来自客户浏览器的每个HTTP 请求创建一个事件。Web 容器将用一个HTTP 响应作出响应。
●Controller（控制器）
控制器接收来自浏览器的请求，并决定将这个请求发往何处。就Struts 而言，控制器是以servlet 实现的一个命令设计模式。struts-config.xml 文件配置控制器。
●业务逻辑
业务逻辑更新模型的状态，并帮助控制应用程序的流程。就Struts 而言，这是通过作为实际业务逻辑“瘦”包装的Action 类完成的。
●Model（模型）的状态
模型表示应用程序的状态。业务对象更新应用程序的状态。ActionForm bean 在会话级或请求级表示模型的状态，而不是在持久级。JSP 文件使用JSP 标记读取来自ActionForm bean 的信息。
●View（视图）
视图就是一个JSP 文件。其中没有流程逻辑，没有业务逻辑，也没有模型信息-- 只有标记。标记是使Struts 有别于其他框架（如Velocity）的因素之一。
详细分析Struts
图3示的是org.apache.struts.action 包的一个最简UML 图。图3显示了ActionServlet (Controller)、ActionForm (Form State) 和Action (Model Wrapper) 之间的最简关系。
图3. Command (ActionServlet) 与Model (Action & ActionForm) 之间的关系的UML 图ActionServlet 类
您还记得函数映射的日子吗？在那时，您会将某些输入事件映射到一个函数指针上。
如果您对此比较熟悉，您会将配置信息放入一个文件，并在运行时加载这个文件。函数指针数组曾经是用 C 语言进行结构化编程的很好方法。
现在好多了，我们有了Java 技术、XML、J2EE，等等。Struts 的控制器是将事件（事件通常是HTTP post）映射到类的一个servlet。正如您所料-- 控制器使用配置文件以使您不必对这些值进行硬编码。时代变了，但方法依旧。
ActionServlet 是该MVC 实现的Command 部分，它是这一框架的核心。ActionServlet (Command) 创建并使用Action 、ActionForm 和ActionForward 。如前所述，struts-config.xml 文件配置该Command。在创建Web 项目时，您将扩展Action 和ActionForm 来解决特定的问题。文件struts-config.xml 指示ActionServlet 如何使用这些扩展的类。这种方法有几个优点：
?应用程序的整个逻辑流程都存储在一个分层的文本文件中。这使得人们更容易查看和理解它，尤其是对于大型应用程序而言。
?网页设计人员不必费力地阅读Java 代码来理解应用程序的流程。
?Java 开发人员也不必在更改流程以后重新编译代码。
可以通过扩展ActionServlet 来添加Command 功能。
ActionForm 类
ActionForm 维护Web 应用程序的会话状态。ActionForm 是一个抽象类，必须为每个输入表单模型创建该类的子类。当我说输入表单模型时,是指ActionForm 表示的是由HTML 表单设置或更新的一般意义上的数据。例如，您可能有一个由HTML 表单设置的UserActionForm 。Struts 框架将执行以下操作：
?检查UserActionForm 是否存在；如果不存在，它将创建该类的一个实例。
?Struts 将使用HttpServletRequest 中相应的域设置UserActionForm 的状态。没有太多讨厌的request.getParameter() 调用。例如，Struts 框架将从请求流中提取fname ，并调用UserActionForm.setFname() 。
?Struts 框架在将UserActionForm 传递给业务包装UserAction 之前将更新它的状态。
?在将它传递给Action 类之前，Struts 还会对UserActionForm 调用validation() 方法进行表单状态验证。注：这并不总是明智之举。别的网页或业务可能使用UserActionForm ，在这些地方，验证可能有所不同。在UserAction 类中进行状态验证可能更好。
?可在会话级维护UserActionForm 。
注：
?struts-config.xml 文件控制HTML 表单请求与ActionForm 之间的映射关系。
?可将多个请求映射到UserActionForm 。
?UserActionForm 可跨多页进行映射，以执行诸如向导之类的操作。Action 类
Action 类是业务逻辑的一个包装。Action 类的用途是将HttpServletRequest 转换为业务逻辑。要使用Action ，请创建它的子类并覆盖process() 方法。
ActionServlet (Command) 使用perform() 方法将参数化的类传递给ActionForm 。仍然没有太多讨厌的request.getParameter() 调用。当事件进展到这一步时，输入表单数据（或HTML 表单数据）已被从请求流中提取出来并转移到ActionForm 类中。
注：扩展Action 类时请注意简洁。Action 类应该控制应用程序的流程，而不应该控制应用程序的逻辑。通过将业务逻辑放在单独的包或EJB 中，我们就可以提供更大的灵活性和可重用性。
考虑Action 类的另一种方式是Adapter 设计模式。Action 的用途是“将类的接口转换为客户机所需的另一个接口。Adapter 使类能够协同工作，如果没有Adapter，则这些类会因为不兼容的接口而无法协同工作。”（摘自Gof 所著的Design Patterns - Elements of Reusable OO Software）。本例中的客户机是ActionServlet ，它对我们的具体业务类接口一无所知。因此，Struts 提供了它能够理解的一个业务接口，即Action 。通过扩展Action ，我们使得我们的业务接口与Struts 业务接口保持兼容。（一个有趣的发现是，Action 是类而不是接口）。Action 开始为一个接口，后来却变成了一个类。真是金无足赤。）Error 类
UML 图（图3）还包括ActionError 和ActionErrors 。ActionError 封装了单个错误消息。ActionErrors 是ActionError 类的容器，View 可以使用标记访问这些类。ActionError 是Struts 保持错误列表的方式。
图4. Command (ActionServlet) 与Model (Action) 之间的关系的UML 图ActionMapping 类
输入事件通常是在HTTP 请求表单中发生的，servlet 容器将HTTP 请求转换为HttpServletRequest 。控制器查看输入事件并将请求分派给某个Action 类。
struts-config.xml 确定Controller 调用哪个Action 类。struts-config.xml 配置信息被转换
为一组ActionMapping ，而后者又被放入ActionMappings 容器中。（您可能尚未注意到这一点，以s结尾的类就是容器）
ActionMapping 包含有关特定事件如何映射到特定Action 的信息。ActionServlet (Command) 通过perform() 方法将ActionMapping 传递给Action 类。这样就使Action 可访问用于控制流程的信息。
ActionMappings
ActionMappings 是ActionMapping 对象的一个集合。
Struts 的优点
?JSP 标记机制的使用
标记特性从JSP 文件获得可重用代码和抽象Java 代码。这个特性能很好地集成到基于JSP 的开发工具中，这些工具允许用标记编写代码。
?标记库
为什么要另发明一种轮子，或标记库呢？如果您在库中找不到您所要的标记，那就自己定义吧。此外，如果您正在学习JSP 标记技术，则Struts 为您提供了一个起点。
?开放源码
您可以获得开放源码的全部优点，比如可以查看代码并让使用库的每个人检查代码。许多人都可以进行很好的代码检查。
?MVC 实现样例
如果您希望创建您自己的MVC 实现，则Struts 可增加您的见识。
?管理问题空间
分治是解决问题并使问题可管理的极好方法。当然，这是一把双刃剑。问题越来越复杂，并且需要越来越多的管理。
Struts 的缺点
?仍处于发展初期
Struts 开发仍处于初级阶段。他们正在向着发行版本1.0 而努力，但与任何1.0 版本一样，它不可能尽善尽美。
?仍在变化中
这个框架仍在快速变化。Struts 1.0 与Struts 0.5 相比变化极大。为了避免使用不赞成使用的方法，您可能隔一天就需要下载最新的Struts。在过去的 6 个月中，我目睹Struts 库从90K 增大到270K 以上。由于Struts 中的变化，我不得不数次修改我的示例，但我不保证我的示例能与您下载的Struts 协同工作。
?正确的抽象级别
Struts 是否提供了正确的抽象级别？对于网页设计人员而言，什么是正确的抽象级别呢？这是一个用$64K 的文字才能解释清楚的问题。在开发网页的过程中，我们是否应该让网页设计人员访问Java 代码？某些框架（如Velocity）说不应该，但它提供了另一种
Web 开发语言让我们学习。在UI 开发中限制访问Java 有一定的合理性。最重要的是，如果让网页设计人员使用一点Java，他将使用大量的Java。在Microsoft ASP 的开发中，我总是看到这样的情况。在ASP 开发中，您应该创建COM 对象，然后编写少量的ASP 脚本将这些COM 对象联系起来。但是，ASP 开发人员会疯狂地使用ASP 脚本。我会听到这样的话，“既然我可以用VBScript 直接编写COM 对象，为什么还要等COM 开发人员来创建它呢？”通过使用标记库，Struts 有助于限制JSP 文件中所需的Java 代码的数量。Logic Tag 就是这样的一种库，它对有条件地生成输出进行管理，但这并不能阻止UI 开发人员对Java 代码的狂热。无论您决定使用哪种类型的框架，您都应该了解您要在其中部署和维护该框架的环境。当然，这项任务真是说起来容易做起来难。
?有限的适用范围
Struts 是一种基于Web 的MVC 解决方案，所以必须用HTML、JSP 文件和servlet 来实现它。
?J2EE 应用程序支持
Struts 需要支持JSP 1.1 和Servlet 2.2 规范的servlet 容器。仅凭这一点远不能解决您的全部安装问题，除非使用Tomcat 3.2。我用Netscape iPlanet 6.0 安装这个库时遇到一大堆问题，按理说它是第一种符合J2EE 的应用程序服务器。我建议您在遇到问题时访问Struts 用户邮件列表的归档资料。
?复杂性
在将问题分为几个部分的同时也引入了复杂性。毫无疑问，要理解Struts 必须接受一定的培训。随着变化的不断加入，这有时会令人很沮丧。欢迎访问本网站。
Struts 的前景
在这个软件开发的新时代，一切都变得很快。在不到 5 年的时间内，我们已经目睹了从cgi/perl 到ISAPI/NSAPI、再到使用VB 的ASP、一直到现在的Java 和J2EE 的变迁。Sun 正在尽力将新的变化反映到JSP/servlet 体系结构中，正如他们对Java 语言和API 所作的更改一样。您可以从Sun 的网站获得新的JSP 1.2 和Servlet 2.3 规范的草案。此外，一个标准JSP 标记库即将出现。
软件开发外文翻译
软件开发外文翻译本页仅作为文档页封面，使用时可以删除 This document is for reference only-rar21year.March
Requirements Phase The chances of a product being developed on time and within budget are somewhat slim unless the members of the software development team agree on what the software product will do. The first step in achieving this unanimity is to analyze the client’s current situation as precisely as possible. For example, it is inadequate to say, “ They need a computer-aided design system because they claim their manual design system, there is lousy. “ Unless the development team knows exactly what is wrong with the current manual system, there is a high probability that aspects of the new computerized system will be equally “lousy. “ Similarly, if a personal computer manufacturer is contemplating development of a new operating system, the first step is to evaluate the firm’s current operating system and analyze carefully exactly why it is unsatisfactory. To take an extreme example, it is vital to know whether the problem exists only in the mind of the sales manager, who blames the operating system for poor sales, or whether users of the operating system are thoroughly disenchanted with its functionality and reliability. Only after a clear picture of the present situation has been gained can the team attempt to answer the critical question, What must the new product be able to do The process of answering this question is carried out during the requirements phase. A commonly held misconception is that , during the requirements phase, the developers must determine what software the client wants. On the contrary, the real objective of the requirements phase is to determine what software the client needs. The problem is that many clients do not know what they need. Furthermore, even a client who has a good idea of what is needed may have difficulty in accurately conveying these ideas to the developers, because most clients are less computer literate than the members of the development team.
软件开发概念和设计方法大学毕业论文外文文献翻译及原文
毕业设计（论文）外文文献翻译 文献、资料中文题目：软件开发概念和设计方法文献、资料英文题目： 文献、资料来源： 文献、资料发表（出版）日期： 院（部）： 专业： 班级： 姓名： 学号： 指导教师： 翻译日期： 2017.02.14
外文资料原文 Software Development Concepts and Design Methodologies During the 1960s, ma inframes and higher level programming languages were applied to man y problems including human resource s yste ms,reservation s yste ms, and manufacturing s yste ms. Computers and software were seen as the cure all for man y bu siness issues were some times applied blindly. S yste ms sometimes failed to solve the problem for which the y were designed for man y reasons including: ?Inability to sufficiently understand complex problems ?Not sufficiently taking into account end-u ser needs, the organizational environ ment, and performance tradeoffs ?Inability to accurately estimate development time and operational costs ?Lack of framework for consistent and regular customer communications At this time, the concept of structured programming, top-down design, stepwise refinement，and modularity e merged. Structured programming is still the most dominant approach to software engineering and is still evo lving. These failures led to the concept of "software engineering" based upon the idea that an engineering-like discipl ine could be applied to software design and develop ment. Software design is a process where the software designer applies techniques and principles to produce a conceptual model that de scribes and defines a solution to a problem. In the beginning, this des ign process has not been well structured and the model does not alwa ys accurately represent the problem of software development. However,design methodologies have been evolving to accommo date changes in technolog y coupled with our increased understanding of development processes. Whereas early desig n methods addressed specific aspects of the
英文文献及中文翻译
毕业设计说明书 英文文献及中文翻译 学院：专 2011年6月 电子与计算机科学技术软件工程
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毕设外文资料翻译.
理工学院 毕业设计外文资料翻译 专业：计算机科学与技术 姓名：马艳丽 学号： 12L0752218 外文出处：The Design and Implementation of 3D Electronic Map of Campus Based on WEBGIS 附件： 1.外文资料翻译译文；2.外文原文。
附件1：外文资料翻译译文 基于WebGIS的校园三维电子地图的设计与实现 一．导言 如今，数字化和信息化是当今时代的主题。随着信息革命和计算机科学的发展，计算机技术已经渗透到科学的各个领域，并引起了许多革命性的变化，在这些科目，古代制图学也不例外。随着技术和文化的不断进步，地图变化的形式和内容也随之更新。在计算机图形学中，地理信息系统（GIS）不断应用到Web，制作和演示的传统方式经历了巨大的变化，由于先进的信息技术的发展，地图的应用已经大大延长。在这些情况下，绘图将面临广阔的发展前景。电子地图是随之应运而生的产品之一。随着计算机技术，计算机图形学理论，遥感技术，航空摄影测量技术和其他相关技术的飞速发展。用户需要的三维可视化，动态的交互性和展示自己的各种地理相关的数据处理和分析，如此多的关注应支付的研究三维地图。东北石油大学及其周边地区的基础上本文设计并建立三维电子地图。 二．系统设计 基于WebGIS的校园三维电子地图系统的具有普通地图的一般特性。通过按键盘上的箭头键（上，下，左，右），可以使地图向相应的方向移动。通过拖动鼠标，可以查看感兴趣的任何一个地方。使用鼠标滚轮，可以控制地图的大小，根据用户的需求来查看不同缩放级别的地图。在地图的左下角会显示当前鼠标的坐标。在一个div层，我们描绘了一个新建筑物的热点，这层可以根据不同的地图图层的显示，它也可以自动调整。通过点击热点，它可以显示热点的具体信息。也可以输入到查询的信息，根据自己的需要，并得到一些相关的信息。此外，通过点击鼠标，人们可以选择检查的三维地图和卫星地图。 主要功能包括： ?用户信息管理：检查用户名和密码，根据权限设置级别的认证，允许不同权限的用户通过互联网登录系统。 ?位置信息查询：系统可以为用户提供模糊查询和快速定位。
计算机专业毕业设计说明书外文翻译(中英对照)
Talking about security loopholes Richard S. Kraus reference to the core network security business objective is to protect the sustainability of the system and data security, This two of the main threats come from the worm outbreaks, hacking attacks, denial of service attacks, Trojan horse. Worms, hacker attacks problems and loopholes closely linked to, if there is major security loopholes have emerged, the entire Internet will be faced with a major challenge. While traditional Trojan and little security loopholes, but recently many Trojan are clever use of the IE loophole let you browse the website at unknowingly were on the move. Security loopholes in the definition of a lot, I have here is a popular saying: can be used to stem the "thought" can not do, and are safety-related deficiencies. This shortcoming can be a matter of design, code realization of the problem. Different perspective of security loo phole s In the classification of a specific procedure is safe from the many loopholes in classification. 1. Classification from the user groups: ● Public loopholes in the software category. If the loopholes in Windows, IE loophole, and so on. ● specialized software loophole. If Oracle loopholes, Apach e,
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外文翻译---硬件软件的设计和开发过程知识讲解
附录 一、英文原文 Hardware/Software Design and Development Process Everett Lumpkin and Michael Gabrick Delphi Corporation, Electronics and Safety Division INTRODUCTION Process and technology advancements in the semiconductor industry have helped to revolutionize automotive and consumer electronics. As Moore’s Law predicted, the increase in complexity and operating frequencies of today’s integrated circuits have enabled the creation of system applications once thought to be impossible. And systems such as camera cell phones, automotive infotainment systems, advanced powertrain controllers and handheld personal computers have been realized as a result. In addition to the increases in process technology, the Electronic Design Automation (EDA) industry has helped to transform the way semiconductor integrated circuits (IC) and subsequent software applications are designed and verified. This transformation has occurred in the form of design abstraction, where the implementation continues to be performed at higher levels through the innovation of design automation tools. An example of this trend is the evolution of software development from the early days of machine-level programming to the C++ and Java software written today. The creation of the assembler allowed the programmer to move a level above machine language, which increased the efficiency of code generation and documentation, but still tied the programmer to the underlying hardware architecture. Likewise, the dawn of C / C++ compilers, debuggers and linkers helped to move the abstraction layer further away from the underlying hardware, making the software completely platform independent, easier to read, easier to debug and more efficient to manage. However, a shift to higher levels of software abstraction has not translated to a reduction in complexity or human resources. On the contrary, as integrated systems have become more feature rich, the complexity of the operating system and corresponding applications have increased rapidly, as have the costs associated with the software implementation and verification activities. Certainly the advancements in embedded software tools such as static code checkers, debuggers and hardware emulators have helped to solve some of the software verification problems, but software verification activities have become more time and resource consuming than the actual software creation. Time-to-market constraints have pushed software verification activities to the system-level, and led to a greater demand for production hardware to be made available earlier in
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外文文献翻译（译成中文2000字左右）： As research laboratories become more automated,new problems are arising for laboratory managers.Rarely does a laboratory purchase all of its automation from a single equipment vendor. As a result,managers are forced to spend money training their users on numerous different software packages while purchasing support contracts for each. This suggests a problem of scalability. In the ideal world,managers could use the same software package to control systems of any size; from single instruments such as pipettors or readers to large robotic systems with up to hundreds of instruments. If such a software package existed, managers would only have to train users on one platform and would be able to source software support from a single vendor. If automation software is written to be scalable, it must also be flexible. Having a platform that can control systems of any size is far less valuable if the end user cannot control every device type they need to use. Similarly, if the software cannot connect to the customer’s Laboratory Information Management System (LIMS) database,it is of limited usefulness. The ideal automation software platform must therefore have an open architecture to provide such connectivity. Two strong reasons to automate a laboratory are increased throughput and improved robustness. It does not make sense to purchase high-speed automation if the controlling software does not maximize throughput of the system. The ideal automation software, therefore, would make use of redundant devices in the system to increase throughput. For example, let us assume that a plate-reading step is the slowest task in a given method. It would make that if the system operator connected another identical reader into the system, the controller software should be able to use both readers, cutting the total throughput time of the reading step in half. While resource pooling provides a clear throughput advantage, it can also be used to make the system more robust. For example, if one of the two readers were to experience some sort of error, the controlling software should be smart enough to route all samples to the working reader without taking the entire system offline. Now that one embodiment of an ideal automation control platform has been described let us see how the use of C++ helps achieving this ideal possible. DISCUSSION C++: An Object-Oriented Language Developed in 1983 by BjarneStroustrup of Bell Labs,C++ helped propel the concept of object-oriented programming into the mainstream.The term ‘‘object-oriented programming language’’ is a familiar phrase that has been in use for decades. But what does it mean? And why is it relevant for automation software? Essentially, a language that is object-oriented provides three important programming mechanisms:
这学期就用了!开题报告、文献检索账号、文献综述、外文翻译、抄袭检测软件
这学期就用了！开题报告、文献检索账号、文献综述、外文翻译、抄袭检测软件、论文目录，都在这了都在这了，有备无患，拿去吧！！来源：齐祥涛的日志 开题报告、文献综述、外文翻译、论文反抄袭软件、论文目录，就差论文正文了，其他都全了！！ 开题报告主要包括以下几个方面： （一）论文名称 论文名称就是课题的名字 第一，名称要准确、规范。准确就是论文的名称要把论文研究的问题是什么，研究的对象是什么交待清楚，论文的名称一定要和研究的内容相一致，不能太大，也不能太小，要准确地把你研究的对象、问题概括出来。 第二，名称要简洁，不能太长。不管是论文或者课题，名称都不能太长，能不要的字就尽量不要，一般不要超过20个字。 （二）论文研究的目的、意义 研究的目的、意义也就是为什么要研究、研究它有什么价值。这一般可以先从现实需要方面去论述，指出现实当中存在这个问题，需要去研究，去解决，本论文的研究有什么实际作用，然后，再写论文的理论和学术价值。这些都要写得具体一点，有针对性一点，不能漫无边际地空喊口号。主要内容包括：⑴研究的有关背景(课题的提出)：即根据什么、受什么启发而搞这项研究。⑵通过分析本地（校）的教育教学实际，指出为什么要研究该课题，研究的价值，要解决的问题。 （三）本论文国内外研究的历史和现状（文献综述）。 规范些应该有，如果是小课题可以省略。一般包括：掌握其研究的广度、深度、已取得的成果；寻找有待进一步研究的问题，从而确定本课题研究的平台(起点)、研究的特色或突破点。 （四）论文研究的指导思想 指导思想就是在宏观上应坚持什么方向，符合什么要求等，这个方向或要求可以是哲学、政治理论，也可以是政府的教育发展规划，也可以是有关研究问题的指导性意见等。 （五）论文写作的目标 论文写作的目标也就是课题最后要达到的具体目的,要解决哪些具体问题，也就是本论文研究要达到的预定目标：即本论文写作的目标定位，确定目标时要紧扣课题,用词要准确、精练、明了。 常见存在问题是：不写研究目标；目标扣题不紧；目标用词不准确；目标定得过高, 对预定的目标没有进行研究或无法进行研究。 确定论文写作目标时，一方面要考虑课题本身的要求，另一方面要考率实际的工作条件与工作水平。 （六）论文的基本内容
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研究钢弧形闸门的动态稳定性 牛志国 河海大学水利水电工程学院，中国南京，邮编210098 nzg_197901@https://www.360docs.net/doc/4915423024.html,，niuzhiguo@https://www.360docs.net/doc/4915423024.html, 李同春 河海大学水利水电工程学院，中国南京，邮编210098 ltchhu@https://www.360docs.net/doc/4915423024.html, 摘要 由于钢弧形闸门的结构特征和弹力，调查对参数共振的弧形闸门的臂一直是研究领域的热点话题弧形弧形闸门的动力稳定性。在这个论文中，简化空间框架作为分析模型，根据弹性体薄壁结构的扰动方程和梁单元模型和薄壁结构的梁单元模型，动态不稳定区域的弧形闸门可以通过有限元的方法，应用有限元的方法计算动态不稳定性的主要区域的弧形弧形闸门工作。此外，结合物理和数值模型，对识别新方法的参数共振钢弧形闸门提出了调查，本文不仅是重要的改进弧形闸门的参数振动的计算方法，但也为进一步研究弧形弧形闸门结构的动态稳定性打下了坚实的基础。 简介 低举升力，没有门槽，好流型，和操作方便等优点，使钢弧形闸门已经广泛应用于水工建筑物。弧形闸门的结构特点是液压完全作用于弧形闸门，通过门叶和主大梁，所以弧形闸门臂是主要的组件确保弧形闸门安全操作。如果周期性轴向载荷作用于手臂，手臂的不稳定是在一定条件下可能发生。调查指出:在弧形闸门的20次事故中，除了极特殊的破坏情况下，弧形闸门的破坏的原因是弧形闸门臂的不稳定;此外，明显的动态作用下发生破坏。例如:张山闸，位于中国的江苏省，包括36个弧形闸门。当一个弧形闸门打开放水时，门被破坏了，而其他弧形闸门则关闭，受到静态静水压力仍然是一样的，很明显，一个动态的加载是造成的弧形闸门破坏一个主要因素。因此弧形闸门臂的动态不稳定是造成弧形闸门(特别是低水头的弧形闸门)破坏的主要原是毫无疑问。