【正文】 ainer can also check the last modified date of the JSP file against the class file. If the JSP file has changed since it was last piled, the container will retranslate and rebuild the page all over again. 大連交通大學(xué)信息工程學(xué)院 2020 屆本科生畢業(yè)設(shè)計(jì) (論文 )外文翻譯 16 Project managers can now assign the presentation layer to HTML developers, who then pass on their work to Java developers to plete the businesslogic portion. The important thing to remember is that a JSP page is really just a servlet. Anything you can do with a servlet, you can do with a JSP. JavaBeans: JavaBeans are Java classes which conform to a set of design patterns that make them easier to use with development tools and other ponents. DEFINITION A JavaBean is a reusable software ponent written in Java. To qualify as a JavaBean, the class must be concrete and public, and have a noargument constructor. JavaBeans expose internal fields as properties by providing public methods that follow a consistent design pattern. Knowing that the property names follow this pattern, other Java classes are able to use introspection to discover and manipulate JavaBean properties. The JavaBean design patterns provide access to the bean’s internal state through two flavors of methods: accessors are used to read a JavaBean’s state。 they do not retrieve them. The mutator for a simple property takes only one parameter in its signature, which can be of any type. Mutators are often nicknamed setters after their prefix. The mutator method signature for a weight property of the type Double would be: public void setWeight(Double weight) A similar design pattern is used to create the accessor method signature. Accessor methods are always prefixed with the lowercase token get, followed by the property name. The first character in the property name must be uppercase. The return value will match the method parameter in the corresponding mutator. Accessors for simple properties cannot accept parameters in their method signature. Not surprisingly, accessors are often called getters. The accessor method signature for our weight property is： public Double getWeight() If the accessor returns a logical value, there is a variant pattern. Instead of using the lowercase token get, a logical property can use the prefix is, followed by the property name. The first character in the property name must be uppercase. The return value will always be a logical value— either boolean or Boolean. Logical accessors cannot accept parameters in their method signature. The boolean accessor method signature for an on property would be public boolean isOn() The canonical method signatures play an important role when working with Java Beans. Other ponents are able to use the Java Reflection API to discover a JavaBean’s properties by looking 大連交通大學(xué)信息工程學(xué)院 2020 屆本科生畢業(yè)設(shè)計(jì) (論文 )外文翻譯 17 for methods prefixed by set, is, or get. If a ponent finds such a signature on a JavaBean, it knows that the method can be used to access or change the bean’s properties. Sun introduced JavaBeans to work with GUI ponents, but they are now used with every aspect of Java development, including web applications. When Sun engineers developed the JSP tag extension classes, they designed them to work with JavaBeans. The dynamic data for a page can be passed as a JavaBean, and the JSP tag can then use the bean’s properties to customize the output. For more on JavaBeans, we highly remend The Awesome Power of JavaBeans, by Lawrence H. Rodrigues [Rodrigues]. The definitive source for JavaBean information is the JavaBean Specification [Sun, JBS]. Model 2: The release of the Servlet/JSP Specification described Model 2 as an architecture that uses servlets and JSP pages together in the same application. The term Model 2 disappeared from later releases, but it remains in popular use among Java web developers. Under Model 2, servlets handle the data access and navigational flow, while JSP pages handle the presentation. Model 2 lets Java engineers and HTML developers each work on their own part of the application. A change in one part of a Model 2 application does not mandate a change to another part of the application. HTML developers can often change the look and feel of an application without changing how the backoffice servlets work. The Struts framework is based on the Model 2 architecture. It provides a controller servlet to handle the navigational flow and special classes to help with the data access. A substantial custom tag library is bundled with the framework to make Struts easy to use with JSP pages. Summary: In this article, we introduced Struts as an application framework. We examined the technology behind HTTP, the Common Gateway Interface, Java servlets, JSPs, and JavaBeans. We also looked at the Model 2 application architecture to see how it is used to bine servlets and JSPs in the same application. Now that you have had a taste of what it is like to develop a web application with Struts, in chapter 2 we dig deeper into the theory and practice behind the Struts architecture. 0 JSP 應(yīng)用框架 什么是應(yīng)用框架： 框架（ framework）是可重用的，半成品的應(yīng)用程序，可以用來產(chǎn)生專門的定制程序。它們運(yùn)行在相似的機(jī)器上，期望從相同的設(shè)備輸入信息，輸出到相同的顯示設(shè)備，并且將數(shù)據(jù)存儲(chǔ)到相同的硬盤設(shè)備。構(gòu)架在這些公共基礎(chǔ)上的應(yīng)用框架可以為開發(fā)人員提供可以為他們的產(chǎn)品提供可重用服務(wù)的基礎(chǔ)架構(gòu)。如果你自己構(gòu)建它，在你完成時(shí)你就會(huì)理解它，但是在你被融入之前又將花費(fèi)多長(zhǎng)時(shí)間呢？如果要購(gòu)買，你必須得克服學(xué)習(xí)曲線，同樣，在你可以用它進(jìn)行工作之前又得花多長(zhǎng)時(shí)間？這里沒有所謂正確答案，但許多觀察者都會(huì)同意，象 Struts 這樣的框架能提供比從頭開始開發(fā)更顯著的投資回報(bào)，特別是對(duì)于大型項(xiàng)目來說。在其它的資料里面，我們也介紹了一些可以 和 Struts 一起使用的框架。與應(yīng)用框架一樣，這些工具也提供了一些半完成的版本，可以用在用戶的定制組件之中。 Struts 以及本文中涉及的組件卻不是這樣。對(duì)于你的工具，如果你可以用來開發(fā) Java, 你就可以用它來開發(fā)Struts。這些技術(shù)并不是專門針對(duì) Struts，而是所有 Java web 應(yīng)用都可以使用的。作為一個(gè) Struts 開發(fā)者，你并不需要知曉所有的相關(guān)知識(shí)，但是這些基本技術(shù)的工作原理可能有助于你針對(duì)棘手問題設(shè)計(jì)出創(chuàng)造性的方案。外交協(xié)議主要設(shè)計(jì)來避免誤解，以及防止談 判破裂。這個(gè)協(xié)議定義數(shù)據(jù)是如何傳輸，以及它們到達(dá)后如何進(jìn)行解碼。 很多服務(wù)器應(yīng)用程序使用 HTTP 之外的其他協(xié)議。應(yīng)用服務(wù)器可以清楚的知道是誰連接上來，而且何時(shí)中斷連接。這稱之為狀態(tài)協(xié)議。 HTTP Server 可以接受來自于各種客戶的各種請(qǐng)求，并提 供各種響應(yīng)，即使是這個(gè)響應(yīng)僅僅是說 No。這也是 Inter 可以擴(kuò)展到很多計(jì)算機(jī)的原因。 HT