【正文】 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. 畢業(yè)設(shè)計(jì)外文翻譯 15 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 畢業(yè)設(shè)計(jì)外文翻譯 16 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 requ。 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。 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。s Java version— the server39。t understand servlet programming. 3. Some tasks are better acplished by servlets than by JSP. JSP is good at generating pages that consist of large sections 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 acplished by a bination of servlets and JSP than by either servlets or JSP alone. Versus JavaScript JavaScript, which is pletely 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 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 peting technology。t understand how JSP works without understanding servlets. 2. JSP consists of static HTML, specialpurpose JSP tags, and Java code. What kind of Java code? Servlet code! You can39。t provide any capabilities that couldn39。s C language is