java大学设备管理系统计算机毕业设计英文文献翻译.doc
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1、毕业设计说明书英文文献及中文翻译班 级:学号:姓 名: 学 院: 软件学院 专 业: 软件工程 指导教师: 2014 年 6 月An Overview of Servlet and JSP Technology Nagle and Wiegley,Aug. 2008,953 958.Abstract: Servlet program running in the server-side, dynamically generated Web page with the traditional CGI and many other similar compared to CGI technolog
2、y, Java Servlet with a more efficient, easier to use, more powerful and has better portability, more savings to invest .Key words: JSP Technology, Servlet, HTTP server1.1 A Servlets JobServlets are Java programs that run on Web or application servers, acting as a middle layer between requests coming
3、 from Web browsers or other HTTP clients and databases or applications on the HTTP server. Their job is to perform the following tasks, as illustrated in Figure 1-1.Figure 1-11Read the explicit data sent by the client.The end user normally enters this data in an HTML form on a Web page. However, the
4、 data could also come from an applet or a custom HTTP client program.2Read the implicit HTTP request data sent by the browser.Figure 1-1 shows a single arrow going from the client to the Web server (the layer where servlets and JSP execute), but there are really two varieties of data: the explicit d
5、ata that the end user enters in a form and the behind-the-scenes HTTP information. Both varieties are critical. The HTTP information includes cookies, information about media types and compression schemes the browser understands, and so on.3Generate the results.This process may require talking to a
6、database, executing an RMI or EJB call, invoking a Web service, or computing the response directly. Your real data may be in a relational database. Fine. But your database probably doesnt speak HTTP or return results in HTML, so the Web browser cant talk directly to the database. Even if it could, f
7、or security reasons, you probably would not want it to. The same argument applies to most other applications.You need the Web middle layer to extract the resultsinside a document.4Send the explicit data (i.e., the document) to the client.This document can be sent in a variety of formats, including t
8、ext (HTML or XML), binary (GIF images), or even a compressed format like gzip that is layered on top of some other underlying format. But, HTML is by far the most common format, so an important servlet/JSP task is to wrap the results inside of HTML.5Send the implicit HTTP response data.Figure 1-1 sh
9、ows a single arrow going from the Web middle layer (the servlet or JSP page) to the client. But, there are really two varieties of data sent: the document itself and the behind-the-scenes HTTP information. Again, both varieties are critical to effective development. Sending HTTP response data involv
10、es telling the browser or other client what type of document is being returned (e.g., HTML), setting cookies and caching parameters, and other such tasks. 1.2 Why Build Web Pages Dynamically?many client requests can be satisfied by prebuilt documents, and the server would handle these requests witho
11、ut invoking servlets. In many cases, however, a static result is not sufficient, and a page needs to be generated for each request. There are a number of reasons why Web pages need to be built on-the-fly:1 The Web page is based on data sent by the client.For instance, the results page from search en
12、gines and order-confirmation pages at online stores are specific to particular user requests. You dont know what to display until you read the data that the user submits. Just remember that the user submits two kinds of data: explicit (i.e., HTML form data) and implicit (i.e., HTTP request headers).
13、 Either kind of input can be used to build the output page. In particular, it is quite common to build a user-specific page based on a cookie value.2The Web page is derived from data that changes frequently.If the page changes for every request, then you certainly need to build the response at reque
14、st time. If it changes only periodically, however, you could do it two ways: you could periodically build a new Web page on the server (independently of client requests), or you could wait and only build the page when the user requests it. The right approach depends on the situation, but sometimes i
15、t is more convenient to do the latter: wait for the user request. For example, a weather report or news headlines site might build the pages dynamically, perhaps returning a previously built page if that page is still up to date.3The Web page uses information from corporate databases or other server
16、-side sources.If the information is in a database, you need server-side processing even if the client is using dynamic Web content such as an applet. Imagine using an applet by itself for a search engine site:Downloading 50 terabyte applet, please wait! Obviously, that is silly; you need to talk to
17、the database. Going from the client to the Web tier to the database (a three-tier approach) instead of from an applet directly to a database (a two-tier approach) provides increased flexibility and security with little or no performance penalty. After all, the database call is usually the rate-limit
18、ing step, so going through the Web server does not slow things down. In fact, a three-tier approach is often faster because the middle tier can perform caching and connection pooling.In principle, servlets are not restricted to Web or application servers that handle HTTP requests but can be used for
19、 other types of servers as well. For example, servlets could be embedded in FTP or mail servers to extend their functionality. And, a servlet API for SIP (Session Initiation Protocol) servers was recently standardized (see http:/jcp.org/en/jsr/detail?id=116). In practice, however, this use of servle
20、ts has not caught on, and well only be discussing HTTP servlets.1.3 The Advantages of Servlets Over Traditional CGIJava servlets are more efficient, easier to use, more powerful, more portable, safer, and cheaper than traditional CGI and many alternative CGI-like technologies.1EfficientWith traditio
21、nal CGI, a new process is started for each HTTP request. If the CGI program itself is relatively short, the overhead of starting the process can dominate the execution time. With servlets, the Java virtual machine stays running and handles each request with a lightweight Java thread, not a heavyweig
22、ht operating system process. Similarly, in traditional CGI, if there are N requests to the same CGI program, the code for the CGI program is loaded into memory N times. With servlets, however, there would be N threads, but only a single copy of the servlet class would be loaded. This approach reduce
23、s server memory requirements and saves time by instantiating fewer objects. Finally, when a CGI program finishes handling a request, the program terminates. This approach makes it difficult to cache computations, keep database connections open, and perform other optimizations that rely on persistent
24、 data. Servlets, however, remain in memory even after they complete a response, so it is straightforward to store arbitrarily complex data between client requests.2ConvenientServlets have an extensive infrastructure for automatically parsing and decoding HTML form data, reading and setting HTTP head
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