【正文】 ，Unix/Linus,MacOS,VMS，和IBM大型機(jī)操作系統(tǒng)之上。它們用在航空業(yè)、電子商務(wù)、在線銀行、web搜索引擎、門戶、大型金融網(wǎng)站、以及成百上千您日常光顧的其他網(wǎng)站。當(dāng)然，僅僅是流行并不能證明技術(shù)的優(yōu)越性。很多泛美的例子。但我們的立場(chǎng)是：服務(wù)器端Java本非一項(xiàng)新的、為經(jīng)證實(shí)的技術(shù)。An Overview of Servlet and JSP Technology Abstract: Servlet program running in the serverside, dynamically generated Web page with the traditional CGI and many other similar pared to CGI technology, Java Servlet with a more efficient, easier to use, more powerful and has better portability, more savings to words: JSP Technology, Servlet, HTTP server A Servlet39。s Job Servlets are Java programs that run on Web or application servers, acting as a middle layer between requests ing from Web browsers or other HTTP clients and databases or applications on the HTTP job is to perform the following tasks, as illustrated in Figure 11 1．Read the explicit data sent by the end user normally enters this data in an HTML form on a Web , the data could also e from an applet or a custom HTTP client ．Read the implicit HTTP request data sent by the 11 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 data that the end user enters in a form and the behindthescenes HTTP varieties are HTTP information includes cookies, information about media types and pression schemes the browser understands, and so ．Generate the process may require talking to a database, executing an RMI or EJB call, invoking a Web service, or puting the response real data may be in a relational your database probably doesn39。t speak HTTP or return results in HTML, so the Web browser can39。t talk directly to the 重慶三峽學(xué)院畢業(yè)設(shè)計(jì)外文翻譯[肖偉]網(wǎng)上購(gòu)物系統(tǒng)設(shè)計(jì)與實(shí)現(xiàn)Even if it could, for security reasons, you probably would not want it same argument applies to most other need the Web middle layer to extract the results inside a ．Send the explicit data(., the document)to the document can be sent in a variety of formats, including text(HTML or XML), binary(GIF images), or even a pressed format like gzip that is layered on top of some other underlying , HTML is by far the most mon format, so an important servlet/JSP task is to wrap the results inside of ．Send the implicit HTTP response 11 shows a single arrow going from the Web middle layer(the servlet or JSP page)to the , there are really two varieties of data sent: the document itself and the behindthescenes HTTP , both varieties are critical to effective HTTP response data involves telling the browser or other client what type of document is being returned(., HTML), setting cookies and caching parameters, and other such Why Build Web Pages Dynamically? many client requests can be satisfied by prebuilt documents, and the server would handle these requests without invoking many cases, however, a static result is not sufficient, and a page needs to be generated for each are a number of reasons why Web pages need to be built onthefly: 1． The Web page is based on data sent by the instance, the results page from search engines and orderconfirmation pages at online stores are specific to particular user don39。t know what to display until you read the data that the user remember that the user submits two kinds of data: explicit(., HTML form data)and implicit(., HTTP request headers).Either kind of input can be used to build the output particular, it is quite mon to build a userspecific page based on a cookie ．The Web page is derived from data that changes the page changes for every request, then you certainly need to build the response at request 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 right approach depends on the situation, but sometimes it is more convenient to do the latter: wait for the user 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 [肖偉]網(wǎng)上購(gòu)物系統(tǒng)設(shè)計(jì)與實(shí)現(xiàn)3．The Web page uses information from corporate databases or other serverside the information is in a database, you need serverside processing even if the client is using dynamic Web content such as an 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 the from the client to the Web tier to the database(a threetier approach)instead of from an applet directly to a database(a twotier approach)provides increased flexibility and security with little or no performance all, the database call is usually the ratelimiting step, so going through the Web server does not slow things fact, a threetier approach is often faster because the middle tier can perform caching and connection principle, servlets are not restricted to Web or application servers that handle HTTP requests but can be used for other types of servers as example, servlets could be embedded in FTP or mail servers to extend their , a servlet API for SIP(Session Initiation Protocol)servers was recently standardized(see ).In practice, however, this use of servlets has not caught on, and we39。ll only be discussing HTTP The Advantages of Servlets Over “Traditional” CGI Java servlets are more efficient, easier to use, more powerful, more portable, safer, and cheaper than traditional CGI and many alternative CGIlike ．Efficient With traditional CGI, a new process is started for each HTTP the CGI program itself is relatively short, the overhead of starting the process can dominate the execution servlets, the Java virtual machine stays running and handles each request with a lightweight Java thread, not a heavyweight operating system , in traditional CGI, if there are N requests to the same CGI program, the code for the CGI program is loaded into memory N servlets, however, there would be N threads, but only a single copy of the servl