电子商务毕业论文外文翻译范文《JavaandtheInternet》.docx

1、电子商务毕业论文外文翻译范文JavaandtheInternet外文文献:Java and the InternetIf Java is, in fact, yet ano ther computer program ming Ian guage, you may question why it is so important and why it is being promoted as a revolutionary step in computer programming. The answer isnt immediately obvious if youre coming from

2、a traditional programming perspective. Although Java is very useful for sol ving traditi onal sta nd-al one program ming problems, it is also importa nt because it will solve program ming problems on the World Wide Web.1.Client-side programmingThe Webs in itial server-browser desig n provided for in

3、 teractive content, but the in teractivity 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 gatheri ng: text-e ntry boxes, check boxes, radio boxes, lists and

4、drop-dow n lists, as well as a butt on 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 passesthrough the Com mon Gateway In terface (CGI) provided on all Web servers. The text with in the submissi on tells CGI what to do w

5、ith it. The most com mon acti on 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 whe n you push a butt on on a Web page, you can sometimes see cgi-b in ” with in all the gobbledygook there.) These

6、programs can be writte n in most Ian guages. Perl is a com mon choice becauseit is desig ned for text mani pulati on and is in terpreted, so it can be in stalled on any server regardless of processor or operat ing system.Many powerful Web sites today are built strictly on CGI, and you can in fact do

7、 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 resp onse time. The resp onse of a CGI program depe nds on how much data must be sent, as well as the load on both the server and the In ternet. (On

8、top of this, start ing a CGI program tends to be slow.) The in itial desig ners of the Web did not foresee how rapidly this ban dwidth would be exhausted for the kinds of applicati ons people developed. For example, any sort of dyn amic graph ing is n early impossible to perform with con siste ncy b

9、ecause a GIF file must be created and moved from the server to the clie nt for each vers ion of the graph. And you e no doubt had direct experienee with something as simple as validati ng the data on an in put form. You press the submit butt on on a page; the data is shipped back to the server; the

10、server starts a CGI program that discovers an error, formats an HTML page informing you of the error, and the n sends the page back to you; you must the n back up a page and try again. Not only is this slow, its inelegant.The soluti on is clie nt-side program ming. Most mach ines that run Web browse

11、rs are powerful engines capable of doing vast work, and with the origi nal static HTML approach they are sitti ng there, just idly wait ing for the server to dish up the n ext page. Clie nt-side program ming means that the Web browser is har nessed to do whatever work it can, and the result for the

12、user is a much speedier and more in teractive experie nee 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 differe nt: a Web browser is like a

13、 limited operati ng system .In the end, you must still program, and this accounts for the dizzying array of problems and solutions produced by clie nt-side program ming. The rest of this secti on provides an overview of the issues and approaches in clie nt-side program ming.2.Plug-insOne of the most

14、 sig ni fica nt steps forward in clie nt-side program ming is the developme nt of the plug-i n. This is a way for a programmer to add new fun cti on ality to the browser by dow nl oadi ng a piece of code that plugs itself into the appropriate spot in the browser. It tells the browser from now on you

15、 can perform 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 isn something youd want to do as part of the process of buildi ng a particular site. The value of the plug

16、-i n for clie nt-side program ming is that it allows an expert programmer to develop a new Ian guage and add that Ian guage to a browser without the permissi on ofthe browser manufacturer. Thus, plug-ins provide a back door” that allows the creation of new client-side programming Ianguages (although

17、 not all Ian guages are impleme nted as plug-i ns).3.Scripting languagesPlug-i ns resulted in an explosi on of scripti ng Ian guages. With a script ing Ianguage you embed the source code for your client-side program directly into the HTML page, and the plug-in that interprets that Ianguage is automa

18、tically activated while the HTML page is being displayed. Scripting Ian guages tend to be reas on ably easy to un dersta nd and, because they are simply text that is part of an HTML page, they load very quickly as part of the sin gle server hit required to procure that page. The trade-off is that yo

19、ur code is exposed for every one to see (and steal). Gen erally, however, you arent doing amaz in gly sophisticated things with scripti ng Ian guages so this is not too much of a hardship.This poi nts out that the script ing Ian guages used in side Web browsers are really inten ded to solve specific

20、 types of problems, primarily the creatio n of richer and more in teractive graphical user in terfaces (GUIs). However, a scripting Ianguage might solve 80 percent of the problems encountered in client-side programming. Your problems might very well fit completely with in that 80 perce nt, and since

21、 scripti ng Ian guages can allow easier and faster developme nt, you should probably con sider a scripti ng Ian guage before look ing at a more invo Ived solutio n such as Java or ActiveX program ming.The most commonly discussed browser scripting Ianguages are JavaScript (which has nothing to do wit

22、h Java; it named that way just to grab some of Javas marketing momentum), VBScript (which looks like Visual Basic), and Tcl/Tk, which comes from the popular cross-platform GUI-building Ianguage. There are others out there, and no doubt more in developme nt.JavaScript is probably the most com monly s

23、upported. It comes built into both Netscape Navigator and the Microsoft Internet Explorer (IE). I n additi on, there are probably more JavaScript books available tha n there are for the other browser Ianguages, and some tools automatically create pages using JavaScript. However, if youre already flu

24、e nt in Visual Basic or Tcl/Tk, you be more productive using those scripti ng Ian guages rather tha n lear ning a new one. (Yo uhave your hands full deali ng with the Web issues already.)4.JavaIf a scripting Ianguage can solve 80 percent of the client-side programming problems, what about the other

25、20 percen the really hard stuff?” The most popular solution today is Java. Not only is it a powerful program ming Ian guage built to be secure, cross-platform, and intern ati on al, but Java is being continually extended to provide Ianguage features and libraries that elegantly handle problems that

26、are difficult in traditional program ming Ian guages, such as multithread ing, database access ,n etwork program ming, and distributed comput ing. Java allows clie nt-side program ming via the applet.An applet is a mi ni-program that will run on ly un der a Web browser. The applet is downloaded auto

27、matically as part of a Web page (just as, for example, a graphic is automatically downloaded). When the applet is activated it executes a program. This is part of its beauty it provides you with a way to automatically distribute the clie nt software from the server at the time the user n eeds the cl

28、ie nt software, and no soon er. The user gets the latest version of the client software without fail and without difficult rei nstallatio n. Because of the way Java is desig ned, the programmer n eeds to create on ly a sin gle program, and that program automatically works with all computers that hav

29、e browsers with built-in Java interpreters. (This safely includes the vast majority of machines.) Since Java is a full-fledged program ming Ian guage, you can do as much work as possible on the clie nt before and after making requests of the server. For example, you won need to send a request form a

30、cross the Internet to discover that yove gotte n a date or some other parameter wrong, and your clie nt computer can quickly do the work of plott ing data in stead of wait ing for the server to make a plot and ship a graphic image back to you. Not only do you get the immediate win of speed and resp

31、on sive ness, but the gen eral n etwork traffic and load on servers can be reduced, preve nting the en tire In ter net from slow ing dow n.One adva ntage a Java applet has over a scripted program is that it in compiled form, so the source code isn available to the clie nt. On the otherhand, a Java a

32、pplet can be decompiled without too much trouble, but hidi ng your code is ofte n n ot an importa nt issue. Two other factors can be importa nt. As you will see later in this book, a compiled Java applet can comprise many modules and take multiple server hits” (accesses) to download. (In Java 1.1 an

33、d higher this is mi ni mized by Java archives, called JAR files, that allow all the required modules to be packaged together and compressedfor a single dow nl oad.) A scripted program will just be in tegrated into the Web page as part of its text (and will gen erally be smaller and reduce server hits). This could be importa nt to th