【正文】 roperties. 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。 外文翻譯原文及譯文 1 JSP application frameworks What 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 organization. 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 2 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 3 Inter has been able to scale to millions of puters. Another reason HTTP has bee the universal standard is its simplicity. An HTTP request looks like an ordinary text document. This has made it easy for applications to make HTTP requests. You can even send an HTTP request by hand using a standard utility such as Tel. When the HTTP response es back, it is also in plain text that developers can read. The first line in the HTTP request contains the method, followed by the location of the requested resource and the version of HTTP. Zero or more HTTP request headers follow the initial line. The HTTP headers provide additional information to the server. This can include the browser type and version, acceptable document types, and the browser’s co