【導(dǎo)讀】因而，從根本上，JSP頁面能夠執(zhí)行的任。何任務(wù)都可以用servler來完成。然而，這種底層的等同性并不意味著servler. 和JSP頁面對于所有的情況都等同適用。問題不在于技術(shù)的能力，而是二者在便。利性、生產(chǎn)率和可維護(hù)性上的不同。畢竟，在特定平臺上能夠用Java編程語言。完成的事情，同樣可以用匯編語言來完成，但是選擇哪種語言依舊十分重要。JSP中6>HTML的編寫與維護(hù)更為簡單。JSP中可以使用常規(guī)的HTML：沒。有額外的反斜杠，沒有額外的雙引號，也沒有暗含的Java語法。能夠使用標(biāo)準(zhǔn)的網(wǎng)站開發(fā)工具。我們也可以使用，因?yàn)樗鼈儠雎訨SP標(biāo)簽。依據(jù)開發(fā)團(tuán)隊(duì)的大小，及項(xiàng)目的復(fù)雜程度，可以對靜態(tài)HTML和。在此，這個(gè)討論并不是讓您停止使用servlets，只使用JSP。針對項(xiàng)目中的某些請求，您可能會在MVC構(gòu)架下組。合使用這兩項(xiàng)技術(shù)。在討論過程中,研討會的主席提出。在公司的一項(xiàng)產(chǎn)品都在JSP出現(xiàn)之前推廣了這種方式。原則上，JSP并沒有提供Servlet不能完成的功能。由于以下4種原因，JSP. 般與JSP的功能并不發(fā)生重疊。

　　

【正文】 ts the Java 2 platform, you use the normal APPLET or Java plugin tag and would do so even if you were using nonJava 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 ., two levels up from WEBINF/classes and output a normal IMG tag. ? You create images that change under the mouse by using clientside JavaScript, referenced with the SCRIPT tag。 this does not change just because the server is using JSP. ? Browsers do not support JSP at all―they merely see the output of the JSP page. So, make sure your JSP outputs HTML patible 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 client. Confusing Translation Time with Request Time A JSP page is converted into a servlet. The servlet is piled, loaded into the server39。s 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 piled 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 _jspService method called for both GET and POST requests , not doGet or doPost. Also, for initialization, they use the jspInit method, not the init page translated into servlet Servlet piled Servlet loaded into server39。s memory jspInit called _jspService called. are application frameworks: A framework is a reusable, semiplete 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 puters, expect input from the same devices, output to the same displays, and 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 mon ground to provide developers with a reusable structure that can serve as the foundation for their own products. A framework provides developers with a set of backbone ponents that have the following characteristics: 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 the anization. Frameworks are the classic buildversusbuy proposition. If you build it, you will understand it when you are done―but how long will it be before you can roll your own? If you buy it, you will have to climb the learning curve―and how long is that going to take? There is no right answer here, but most observers would agree that frameworks such as Struts provide a significant return on investment pared 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 ponentsas well. 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 semiplete versions of a subsystem that can be specialized to provide a custom ponent. 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 choices among Struts developers. If you can use it with Java, you can use it with Struts. Enabling technologies: Applications developed with Struts are based on a number of enabling ponents are not specific to Struts and underlie every Java web application. A reason that developers use frameworks like Struts is to hide the nasty details behind acronyms like HTTP, CGI, and JSP. As a Struts developer, you don’t need to be an alphabet soup guru, but a working knowledge of these base technologies can help you devise creative solutions to tricky problems. Hypertext Transfer Protocol HTTP : When mediating talks between nations, diplomats often follow a formal protocol. Diplomatic protocols are designed to avoid misunderstandings and to keep negotiations from breaking down. In a similar vein, when puters need to talk, they also follow a formal protocol. The protocol defines how data is transmitted and how to decode it once it arrives. Web applications use the Hypertext Transfer Protocol HTTP to move data between the browser running on your puter and the application running on the server. Many server applications municate using protocols other than HTTP. Some of these maintain an ongoing connection between the puters. The application server knows exactly who is connected at all times and can tell when a connection is dropped. Because they know the state of each connection and the identity of each person using it, these are known as stateful protocols. By contrast, HTTP is known as a stateless protocol. An HTTP server will accept any request from any client and will always provide some type of response, even if the response is just to say no. Without the overhead of negotiating and retaining a connection, stateless protocols can handle a large volume of requests. This is one reason why the Inter has been able to scale to millions of puters. Another reason HTTP has bee the universal standard is its simp