计算机专业外文翻译---JSP 应用框架

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1、 JSP application frameworks What are application frameworks: 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 fr

2、om 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 common ground

3、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 components that have the following characteristics: 1.They are known to work well in other applications. 2. They are ready to use with the n

4、ext project. 3. They can also be used by other teams in the organization. Frameworks are the classic build-versus-buy 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

5、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 compared to starting from scratch, especially for larger projects. Other types of frameworks: The idea of a framework applies no

6、t only to applications but to application componentsas 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

7、 tools provide semi-complete versions of a subsystem that can 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 envir

8、onment 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 technologies.These comp

9、onents 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 dont need to be an alphabet soup guru, but a working knowledge of these base

10、 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

11、similar vein, when computers 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 computer and the application

12、running on the server. Many server applications communicate using protocols other than HTTP. Some of these maintain an ongoing connection between the computers. The application server knows exactly who is connected at all times and can tell when a connection is dropped. Because they know the state o

13、f 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

14、 the overhead of negotiating and retaining a connection, stateless protocols can handle a large volume of requests. This is one reason why the Internet has been able to scale to millions of computers. Another reason HTTP has become the universal standard is its simplicity. An HTTP request looks like

15、 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 Telnet. When the HTTP response comes back, it is also in plain text that developers can read. The first line in the HTTP request contai

16、ns 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 brows

17、ers cookies, just to name a few. Of the seven request methods, GET and POST are by far the most popular. Once the server has received and serviced the request, it will issue an HTTP response. The first line in the response is called the status line and carries the HTTP protocol version, a numeric st

18、atus, and a brief description of the status. Following the status line, the server will return a set of HTTP response headers that work in a way similar to the request headers. As we mentioned, HTTP does not preserve state information between requests.The server logs the request, sends the response,

19、 and goes blissfully on to the next request. While simple and efficient, a stateless protocol is problematic for dynamic applications that need to keep track of their users. (Ignorance is not always bliss. Cookies and URL rewriting are two common ways to keep track of users between requests. A cooki

20、e is a special packet of information on the users computer. URL rewriting stores a special reference in the page address that a Java server can use to track users. Neither approach is seamless, and using either means extra work when developing a web application. On its own, a standard HTTP web serve

21、r does not traffic in dynamic content. It mainly uses the request to locate a file and then returns that file in the response. The file is typically formatted using Hypertext Markup Language (HTML) W3C, HTML that the web browser can format and display. The HTML page often includes hypertext links to

22、 other web pages and may display any number of other goodies, such as images and videos. The user clicks a link to make another request, and the process begins a new. Standard web servers handle static content and images quite well but need a helping hand to provide users with a customized, dynamic response.