JSP技术概述与应用框架外文翻译毕业设计(共20页).doc

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1、精选优质文档-倾情为你奉上附件1：外文原文Overview of JSP Technology and JSP application frameworks1 Benefits of JSP JSP pages are translated into servlets. So, fundamentally, any task JSP pages can perform could also be accomplished by servlets. However, this underlying equivalence does not mean that servlets and JSP p

2、ages are equally appropriate in all scenarios. The issue is not the power of the technology, it is the convenience, productivity, and maintainability of one or the other. After all, anything you can do on a particular computer platform in the Java programming language you could also do in assembly l

3、anguage. But it still matters which you choose.JSP provides the following benefits over servlets alone: It is easier to write and maintain the HTML. Your static code is ordinary HTML: no extra backslashes, no double quotes, and no lurking Java syntax. You can use standard Web-site development tools.

4、 Even HTML tools that know nothing about JSP can be used because they simply ignore the JSP tags. You can divide up your development team. The Java programmers can work on the dynamic code. The Web developers can concentrate on the presentation layer. On large projects, this division is very importa

5、nt. Depending on the size of your team and the complexity of your project, you can enforce a weaker or stronger separation between the static HTML and the dynamic content. Now, this discussion is not to say that you should stop using servlets and use only JSP instead. By no means. Almost all project

6、s will use both. For some requests in your project, you will use servlets. For others, you will use JSP. For still others, you will combine them with the MVC architecture . You want the appropriate tool for the job, and servlets, by themselves, do not complete your toolkit.2.Advantages of JSP Over C

7、ompeting Technologies A number of years ago, Marty was invited to attend a small 20-person industry roundtable discussion on software technology. Sitting in the seat next to Marty was James Gosling, inventor of the Java programming language. Sitting several seats away was a high-level manager from a

8、 very large software company in Redmond, Washington. During the discussion, the moderator brought up the subject of Jini, which at that time was a new Java technology. The moderator asked the manager what he thought of it, and the manager responded that it was too early to tell, but that it seemed t

9、o be an excellent idea. He went on to say that they would keep an eye on it, and if it seemed to be catching on, they would follow his companys usual embrace and extend strategy. At this point, Gosling lightheartedly interjected You mean disgrace and distend. Now, the grievance that Gosling was airi

10、ng was that he felt that this company would take technology from other companies and suborn it for their own purposes. But guess what? The shoe is on the other foot here. The Java community did not invent the idea of designing pages as a mixture of static HTML and dynamic code marked with special ta

11、gs. For example, ColdFusion did it years earlier. Even ASP (a product from the very software company of the aforementioned manager) popularized this approach before JSP came along and decided to jump on the bandwagon. In fact, JSP not only adopted the general idea, it even used many of the same spec

12、ial tags as ASP did.So, the question becomes: why use JSP instead of one of these other technologies? Our first response is that we are not arguing that everyone should. Several of those other technologies are quite good and are reasonable options in some situations. In other situations, however, JS

13、P is clearly better. Here are a few of the reasons.2.1 Versus .NET and Active Server Pages (ASP). NET is well-designed technology from Microsoft. ASP.NET is the part that directly competes with servlets and JSP. The advantages of JSP are two fold.First, JSP is portable to multiple operating systems

14、and Web servers; you arent locked into deploying on Windows and IIS. Although the core .NET platform runs on a few non-Windows platforms, the ASP part does not. You cannot expect to deploy serious ASP.NET applications on multiple servers and operating systems. For some applications, this difference

15、does not matter. For others, it matters greatly.Second, for some applications the choice of the underlying language matters greatly. For example, although .NETs C# language is very well designed and is similar to Java, fewer programmers are familiar with either the core C# syntax or the many auxilia

16、ry libraries. In addition, many developers still use the original version of ASP. With this version, JSP has a clear advantage for the dynamic code. With JSP, the dynamic part is written in Java, not VBScript or another ASP-specific language, so JSP is more powerful and better suited to complex appl

17、ications that require reusable components. You could make the same argument when comparing JSP to the previous version of ColdFusion; with JSP you can use Java for the real code and are not tied to a particular server product. However, the current release of ColdFusion is within the context of a J2E

18、E server, allowing developers to easily mix ColdFusion and servlet/JSP code.2.2 Versus PHP PHP (a recursive acronym for PHP: Hypertext Preprocessor) is a free, open-source, HTML-embedded scripting language that is somewhat similar to both ASP and JSP. One advantage of JSP is that the dynamic part is

19、 written in Java, which already has an extensive API for networking, database access, distributed objects, and the like, whereas PHP requires learning an entirely new, less widely used language. A second advantage is that JSP is much more widely supported by tool and server vendors than is PHP.2.3 V

20、ersus Pure Servlets JSP doesnt provide any capabilities that couldnt, in principle, be accomplished with servlets. In fact, JSP documents are automatically translated into servlets behind the scenes. But it is more convenient to write (and to modify!) regular HTML than to use a zillion println state

21、ments to generate the HTML. Plus, by separating the presentation from the content, you can put different people on different tasks: your Web page design experts can build the HTML by using familiar tools and either leave places for your servlet programmers to insert the dynamic content or invoke the

22、 dynamic content indirectly by means of XML tags.Does this mean that you can just learn JSP and forget about servlets? Absolutely not! JSP developers need to know servlets for four reasons: 1. JSP pages get translated into servlets. You cant understand how JSP works without understanding servlets. 2

23、. JSP consists of static HTML, special-purpose JSP tags, and Java code. What kind of Java code? Servlet code! You cant write that code if you dont understand servlet programming. 3. Some tasks are better accomplished by servlets than by JSP. JSP is good at generating pages that consist of large sect

24、ions of fairly well structured HTML or other character data. Servlets are better for generating binary data, building pages with highly variable structure, and performing tasks (such as redirection) that involve little or no output. 4. Some tasks are better accomplished by a combination of servlets

25、and JSP than by either servlets or JSP alone. 2.4 Versus JavaScript JavaScript, which is completely distinct from the Java programming language, is normally used to dynamically generate HTML on the client, building parts of the Web page as the browser loads the document. This is a useful capability

26、and does not normally overlap with the capabilities of JSP (which runs only on the server). JSP pages still include SCRIPT tags for JavaScript, just as normal HTML pages do. In fact, JSP can even be used to dynamically generate the JavaScript that will be sent to the client. So, JavaScript is not a

27、competing technology; it is a complementary one. It is also possible to use JavaScript on the server, most notably on Sun ONE (formerly iPlanet), IIS, and BroadVision servers. However, Java is more powerful, flexible, reliable, and portable.2.5 Versus WebMacro or Velocity JSP is by no means perfect.

28、 Many people have pointed out features that could be improved. This is a good thing, and one of the advantages of JSP is that the specification is controlled by a community that draws from many different companies. So, the technology can incorporate improvements in successive releases. However, some

29、 groups have developed alternative Java-based technologies to try to address these deficiencies. This, in our judgment, is a mistake. Using a third-party tool like Apache Struts that augments JSP and servlet technology is a good idea when that tool adds sufficient benefit to compensate for the addit

30、ional complexity. But using a nonstandard tool that tries to replace JSP is a bad idea. When choosing a technology, you need to weigh many factors: standardization, portability, integration, industry support, and technical features. The arguments for JSP alternatives have focused almost exclusively

31、on the technical features part. But portability, standardization, and integration are also very important. For example, the servlet and JSP specifications define a standard directory structure for Web applications and provide standard files (.war files) for deploying Web applications. All JSP-compat

32、ible servers must support these standards. Filters can be set up to apply to any number of servlets or JSP pages, but not to nonstandard resources. The same goes for Web application security settings. Besides, the tremendous industry support for JSP and servlet technology results in improvements tha

33、t mitigate many of the criticisms of JSP. For example, the JSP Standard Tag Library and the JSP 2.0 expression language address two of the most well-founded criticisms: the lack of good iteration constructs and the difficulty of accessing dynamic results without using either explicit Java code or ve

34、rbose jsp:useBean elements.3. Misconceptions About JSP Forgetting JSP Is Server-Side Technology Here are some typical questions Marty has received (most of them repeatedly). Our server is running JDK 1.4. So, how do I put a Swing component in a JSP page? How do I put an image into a JSP page? I do n

35、ot know the proper Java I/O commands to read image files. Since Tomcat does not support JavaScript, how do I make images that are highlighted when the user moves the mouse over them? Our clients use older browsers that do not understand JSP. What should we do? When our clients use View Source in a b

36、rowser, how can I prevent them from seeing the JSP tags? All of these questions are based upon the assumption that browsers know something about the server-side process. But they do not. Thus: For putting applets with Swing components into Web pages, what matters is the browsers Java versionthe serv

37、ers version is irrelevant. If the browser supports the Java 2 platform, you use the normal APPLET (or Java plug-in) tag and would do so even if you were using non-Java technology on the server. You do not need Java I/O to read image files; you just put the image in the directory for Web resources (i

38、.e., two levels up from WEB-INF/classes) and output a normal IMG tag. You create images that change under the mouse by using client-side JavaScript, referenced with the SCRIPT tag; this does not change just because the server is using JSP. Browsers do not support JSP at allthey merely see the output

39、 of the JSP page. So, make sure your JSP outputs HTML compatible with the browser, just as you would do with static HTML pages. And, of course you need not do anything to prevent clients from seeing JSP tags; those tags are processed on the server and are not part of the output that is sent to the c

40、lient.Confusing Translation Time with Request Time A JSP page is converted into a servlet. The servlet is compiled, loaded into the servers memory, initialized, and executed. But which step happens when? To answer that question, remember two points: The JSP page is translated into a servlet and comp

41、iled only the first time it is accessed after having been modified. Loading into memory, initialization, and execution follow the normal rules for servlets. The most frequently misunderstood entries are highlighted. When referring to the table, note that servlets resulting from JSP pages use the _js

42、pService method (called for both GET and POST requests), not doGet or doPost. Also, for initialization, they use the jspInit method, not the init method.JSP page translated into servlet Servlet compiled Servlet loaded into servers memory jspInit called _jspService called.4.What are application frame

43、works: A framework is a reusable, semi-complete application that can be specialized to produce custom applications Johnson. Like people, software applications are more alike than they are different. They run on the same computers, expect input from the same devices, output to the same displays, and

44、save data to the same hard disks. Developers working on conventional desktop applications are accustomed to toolkits and development environments that leverage the sameness between applications. Application frameworks build on this common ground to provide developers with a reusable structure that c

45、an serve as the foundation for their own products. A framework provides developers with a set of backbone components that have the following characteristics:1.They are known to work well in other applications.2. They are ready to use with the next project.3. They can also be used by other teams in t

46、he organization. Frameworks are the classic build-versus-buy proposition. If you build it, you will understand it when you are donebut how long will it be before you can roll your own? If you buy it, you will have to climb the learning curveand how long is that going to take? There is no right answe

47、r here, but most observers would agree that frameworks such as Struts provide a significant return on investment compared to starting from scratch, especially for larger projects.Other types of frameworks: The idea of a framework applies not only to applications but to application componentsas well.

48、 Throughout this article, we introduce other types of frameworks that you can use with Struts. These include the Lucene search engine, the Scaffold toolkit, the Struts validator, and the Tiles tag library. Like application frameworks, these tools provide semi-complete versions of a subsystem that ca

49、n be specialized to provide a custom component.Some frameworks have been linked to a proprietary development environment. This is not the case with Struts or any of the other frameworks shown in this book. You can use any development environment with Struts: Visual Age for Java, JBuilder, Eclipse, Emacs, and Textpad are all popular c