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1、院 （系）: 计算机学院 专 业: 计算机科学与技术 班 级: 学生姓名: 导师姓名: 职称:起止时间:2011年 9月23日 至 2012年 6月2日 原文:Java and the Internet Although Java is very useful for solving traditional stand-alone programming problems, it is also important because it will solve programming problems on the World Wide Web. 1. Client-side programmi

2、ng The Webs initial server-browser design provided for interactive content, but the interactivity was completely provided by the server. The server produced static pages for the client browser, which would simply interpret and display them. Basic HTML contains simple mechanisms for data gathering: t

3、ext-entry boxes, check boxes, radio boxes, lists and drop-down lists, as well as a button that can only be programmed to reset the data on the form or “submit” the data on the form back to the server. This submission passes through the Common Gateway Interface （CGI） provided on all Web servers. The

4、text within the submission tells CGI what to do with it. The most common action is to run a program located on the server in a directory thats typically called “cgi-bin.” （If you watch the address window at the top of your browser when you push a button on a Web page, you can sometimes see “cgi-bin”

5、 within all the gobbledygook there.） These programs can be written in most languages. Perl is a common choice because it is designed for text manipulation and is interpreted, so it can be installed on any server regardless of processor or operating system. Many powerful Web sites today are built str

6、ictly on CGI, and you can in fact do nearly anything with it. However, Web sites built on CGI programs can rapidly become overly complicated to maintain, and there is also the problem of response time. The response of a CGI program depends on how much data must be sent, as well as the load on both t

7、he server and the Internet. （On top of this, starting a CGI program tends to be slow.） The initial designers of the Web did not foresee how rapidly this bandwidth would be exhausted for the kinds of applications people developed. For example, any sort of dynamic graphing is nearly impossible to perf

8、orm with consistency because a GIF file must be created and moved from the server to the client for each version of the graph. And youve no doubt had direct experience with something as simple as validating the data on an input form. You press the submit button on a page; the data is shipped back to

9、 the server; the server starts a CGI program that discovers an error, formats an HTML page informing you of the error, and then sends the page back to you; you must then back up a page and try again. Not only is this slow, its inelegant. The solution is client-side programming. Most machines that ru

10、n Web browsers are powerful engines capable of doing vast work, and with the original static HTML approach they are sitting there, just idly waiting for the server to dish up the next page. Client-side programming means that the Web browser is harnessed to do whatever work it can, and the result for

11、 the user is a much speedier and more interactive experience at your Web site. The problem with discussions of client-side programming is that they arent very different from discussions of programming in general. The parameters are almost the same, but the platform is different: a Web browser is lik

12、e a limited operating system. In the end, you must still program, and this accounts for the dizzying array of problems and solutions produced by client-side programming. The rest of this section provides an overview of the issues and approaches in client-side programming. 2.Plug-ins One of the most

13、significant steps forward in client-side programming is the development of the plug-in. This is a way for a programmer to add new functionality to the browser by downloading a piece of code that plugs itself into the appropriate spot in the browser. It tells the browser “from now on you can perform

14、this new activity.” （You need to download the plug-in only once.） Some fast and powerful behavior is added to browsers via plug-ins, but writing a plug-in is not a trivial task, and isnt something youd want to do as part of the process of building a particular site. The value of the plug-in for clie

15、nt-side programming is that it allows an expert programmer to develop a new language and add that language to a browser without the permission of the browser manufacturer. Thus, plug-ins provide a “back door” that allows the creation of new client-side programming languages （although not all languag

16、es are implemented as plug-ins）. 3.Scripting languages Plug-ins resulted in an explosion of scripting languages. With a scripting language you embed the source code for your client-side program directly into the HTML page, and the plug-in that interprets that language is automatically activated while the HTML page is being displayed. Scripting languages tend to be reasonably easy to understand and,