基于JSP銷售系統(tǒng)設(shè)計(jì)與實(shí)現(xiàn)的中英文翻譯

1、外文文獻(xiàn)及翻譯 An Overview of Servlet and JSP Technology Servlet program running in the server-side, dynamically generated Web page with the traditional CGI and many other similar compared to CGI technology, Java Servlet with a more efficient, easier to use, more powerful and has better portability, more s

2、avings to invest . Key words: JSP Technology, Servlet, HTTP server . 1.1 A Servlet's Job Servlets are Java programs that run on Web or application servers, acting as a middle layer between requests coming from Web browsers or other HTTP clients and databases or applications on the HTTP server. T

3、heir job is to perform the following tasks, Read the explicit data sent by the client. The end user normally enters this data in an HTML form on a Web page. However, the data could also come from an applet or a custom HTTP client program. 1Read the implicit HTTP request data sent by the browser. arr

4、ow going from 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 behind-the-scenes HTTP information. Both varieties are critical. The HTTP information includes cookies, information about

5、media types and compression schemes the browser understands, and so on. 2Generate the results. This process may require talking to a 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 data

6、base probably doesn't speak HTTP or return results in HTML, so the Web browser can't talk directly to the database. Even if it could, for 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 res

7、ults inside a document. 3Send the explicit data (i.e., the document) to the client. 8 This document can be sent in a variety of formats, including text (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 fa

8、r the most common format, so an important servlet/JSP task is to wrap the results inside of HTML. 4Send the implicit HTTP response data. Figure 1-1 shows 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 docu

9、ment itself and the behind-the-scenes HTTP information. Again, both varieties are critical to effective development. Sending HTTP response data involves telling the browser or other client what type of document is being returned (e.g., HTML), setting cookies and caching parameters, and other such ta

10、sks. 1.2 Why Build Web Pages Dynamically? many client requests can be satisfied by prebuilt documents, and the server would handle these requests without 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 numbe

11、r of reasons why Web pages need to be built on-the-fly: 1The Web page is based on data sent by the client. For instance, the results page from search engines and order-confirmation pages at online stores are specific to particular user requests. You don't know what to display until you read the

12、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). 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 v

13、alue. 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 request time. If it changes only periodically, however, you could do it two ways: you could periodically build a new Web page on the server (indep

14、endently 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 it 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

15、dynamically, perhaps returning a previously built page if that page is still up to date. 3. The Web page uses information from corporate databases or other serverserver-side sources. If the information is in a database, you need server-side processing even if the client is using dynamic Web content

16、such as an applet. Imagine using 9 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 database. Going from the client to the Web tier to the database (a three-tier approach) instead of from an apple

17、t 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-limiting step, so going through the Web server does not slow things down. In fact, a three-tier approach is often faster

18、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 other types of servers as well. For example, servlets could be embedded in FTP or mail servers to extend their fun

19、ctionality. And, a servlet API for SIP (Session Initiation Protocol) servers was recently standardized (see /en/jsr/detail?id=116). In practice, however, this use of servlets has not caught on, and we'll only be discussing HTTP servlets. Advantages . 1.3 The Advantages of Servlets O

20、ver "Traditional" CGI Java servlets are more efficient, easier to use, more powerful, more portable, safer, and cheaper than traditional CGI and many alternative CGI-like technologies. 1Efficient With traditional CGI, a new process is started for each HTTP request. If the CGI program itsel

21、f 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 heavyweight operating system process. Similarly, in traditional CGI, if there are N reques

22、ts 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 reduces server memory requirements and saves time by instantiating fewer objects. Final

23、ly, 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 data. Servlets, however, remain in memory even after they complete a response, s

24、o it is straightforward to store arbitrarily complex data between client requests. 2Convenient Servlets have an extensive infrastructure for automatically parsing and decoding HTML form data, reading and setting HTTP headers, handling cookies, tracking sessions, and many other such high-level utilit

25、ies. In CGI, you have to do much of this yourself. Besides, if you already know the Java programming language, why learn Perl too? You're already convinced that Java technology 10 makes for more reliable and reusable code than does Visual Basic, VBScript, or C+. Why go back to those languages fo

26、r server-side programming? 3. Powerful Servlets support several capabilities that are difficult or impossible to accomplish with regular CGI. Servlets can talk directly to the Web server, whereas regular CGI programs cannot, at least not without using a server-specific API. Communicating with the We

27、b server makes it easier to translate relative URLs into concrete path names, for instance. Multiple servlets can also share data, making it easy to implement database connection pooling and similar resource-sharing optimizations. Servlets can also maintain information from request to request, simpl

28、ifying techniques like session tracking and caching of previous computations. 4Portable Servlets are written in the Java programming language and follow a standard API. Servlets are supported directly or by a plugin on virtually every major Web server. Consequently, servlets written for, say, Macrom

29、edia JRun can run virtually unchanged on Apache Tomcat, Microsoft Internet Information Server (with a separate plugin), IBM WebSphere, iPlanet Enterprise Server, Oracle9i AS, or StarNine WebStar. They are part of the Java 2 Platform, Enterprise Edition (J2EE; see so industry support for servlets is

30、becoming even more pervasive. 5Inexpensive Inexpensive A number of free or very inexpensive Web servers are good for development use or deployment of low- or medium-volume Web sites. Thus, with servlets and JSP you can start with a free or inexpensive server and migrate to more expensive servers wit

31、h high-performance capabilities or advanced administration utilities only after your project meets initial success. This is in contrast to many of the other CGI alternatives, which require a significant initial investment for the purchase of a proprietary package. Price and portability are somewhat

32、connected. For example, Marty tries to keep track of the countries of readers that send him questions by email. India was near the top of the list, probably #2 behind the U.S. Marty also taught one of his JSP and servlet training courses (see in Manila, and there was great interest in servlet and JS

33、P technology there. Now, why are India and the Philippines both so interested? We surmise that the answer is twofold. First, both countries have large pools of well-educated software developers. Second, both countries have (or had, at that time) highly unfavorable currency exchange rates against the

34、 U.S. dollar. So, buying a special-purpose Web server from a U.S. company consumed a large part of early project funds. 11 But, with servlets and JSP, they could start with a free server: Apache Tomcat (either standalone, embedded in the regular Apache Web server, or embedded in Microsoft IIS). Once

35、 the project starts to become successful, they could move to a server like Caucho Resin that had higher performance and easier administration but that is not free. But none of their servlets or JSP pages have to be rewritten. If their project becomes even larger, they might want to move to a distrib

36、uted (clustered) environment. No problem: they could move to Macromedia JRun Professional, which supports distributed applications (Web farms). Again, none of their servlets or JSP pages have to be rewritten. If the project becomes quite large and complex, they might want to use Enterprise JavaBeans

37、 (EJB) to encapsulate their business logic. So, they might switch to BEA WebLogic or Oracle9i AS. Again, none of their servlets or JSP pages have to be rewritten. Finally, if their project becomes even bigger, they might move it off of their Linux box and onto an IBM mainframe running IBM WebSphere.

38、 But once again, none of their servlets or JSP pages have to be rewritten. 6Secure One of the main sources of vulnerabilities in traditional CGI stems from the fact that the programs are often executed by general-purpose operating system shells. So, the CGI programmer must be careful to filter out c

39、haracters such as backquotes and semicolons that are treated specially by the shell. Implementing this precaution is harder than one might think, and weaknesses stemming from this problem are constantly being uncovered in widely used CGI libraries. A second source of problems is the fact that some C

40、GI programs are processed by languages that do not automatically check array or string bounds. For example, in C and C+ it is perfectly legal to allocate a 100-element array and then write into the 999th "element," which is really some random part of program memory. So, programmers who for

41、get to perform this check open up their system to deliberate or accidental buffer overflow attacks. Servlets suffer from neither of these problems. Even if a servlet executes a system call (e.g., with Runtime.exec or JNI) to invoke a program on the local operating system, it does not use a shell to

42、do so. And, of course, array bounds checking and other memory protection features are a central part of the Java programming language. 7Mainstream There are a lot of good technologies out there. But if vendors don't support them and developers don't know how to use them, what good are they?

43、Servlet and JSP technology is supported by servers from Apache, Oracle, IBM, Sybase, BEA, Macromedia, Caucho, Sun/iPlanet, New Atlanta, ATG, Fujitsu, Lutris, Silverstream, the World Wide Web Consortium (W3C), and many others. Several low-cost plugins add support to Microsoft IIS and Zeus as well. Th

44、ey run on Windows, Unix/Linux, MacOS, VMS, and IBM mainframe operating systems. 12 They are the single most popular application of the Java programming language. They are arguably the most popular choice for developing medium to large Web applications. They are used by the airline industry (most Uni

45、ted Airlines and Delta Airlines Web sites), e-commerce (), online banking (First USA Bank, Banco Popular de Puerto Rico), Web search engines/portals (), large financial sites (American Century Investments), and hundreds of other sites that you visit every day. Of course, popularity alone is no proof

46、 of good technology. Numerous counter-examples abound. But our point is that you are not experimenting with a new and unproven technology when you work with server-side Java. 基于JSP的在線銷售系統(tǒng)的設(shè)計(jì)與實(shí)現(xiàn)Servlet 程序在服務(wù)器端運(yùn)行，動(dòng)態(tài)地生成 Web 頁(yè)面與傳統(tǒng)的 CGI 和許多其他類似 CGI 的技術(shù)相比，Java Servlet 具有更高的效率，更容易使用，功能更強(qiáng)大，具有更好的可移植性，更節(jié)省投資。關(guān)

47、鍵詞：JSP 技術(shù), Servlet, HTTP server 1.1Servlet 的功能 Servlets 是運(yùn)行在 Web 或應(yīng)用服務(wù)器上的 Java 程序，它是一個(gè)中間層，負(fù)責(zé)連接來(lái)自 Web 瀏覽器或其他 HTTP 客戶程序的請(qǐng)求和 HTTP 服務(wù)器上的數(shù)據(jù)庫(kù)或應(yīng)用程序。Servlet 的工作是執(zhí)行西門的任務(wù)，Web 中間件的作用讀取客戶發(fā)送的顯式數(shù)據(jù)。 1、讀取客戶發(fā)送的顯式數(shù)據(jù)。最終用戶一般在頁(yè)面的 HTML 表單中輸入這些數(shù)據(jù)。然而，數(shù)據(jù)還有可能來(lái)自 applet 或定制的 HTTP 客戶程序。讀取由瀏覽器發(fā)送的隱式請(qǐng)求數(shù)據(jù)。讀取由瀏覽器發(fā)送的隱式請(qǐng)求數(shù)據(jù)?？蛻舳藗魉偷?Web

48、 服務(wù)器的數(shù)據(jù)有兩種，它們分別為用戶在表單中輸入的顯式數(shù)據(jù)，以及后臺(tái)的 HTTP 信息。兩種數(shù)據(jù)都很重要。HTTP 信息包括 cookie、瀏覽器所能識(shí)別的媒體類型和壓縮模式等。 2、生成結(jié)果。這個(gè)過(guò)程可能需要訪問(wèn)數(shù)據(jù)庫(kù)、執(zhí)行 RMI 或 EJB 調(diào)用、調(diào)用 Web 服務(wù)，或者直接計(jì)算得出對(duì)應(yīng)的響應(yīng)。實(shí)際的數(shù)據(jù)可能存儲(chǔ)在關(guān)系型數(shù)據(jù)庫(kù)中。該數(shù)據(jù)庫(kù)可能不理解 HTTP，或者不能返回 HTML 形式的結(jié)果，所有 Web 瀏覽器不能直接與數(shù)據(jù)庫(kù)進(jìn)行會(huì)話。即使它能夠做到這一點(diǎn)，為了安全上的考慮，我們也不希望讓它這么做。對(duì)應(yīng)大多數(shù)其他應(yīng)用程序，也存在類似的問(wèn)題。因此，我們需要 Web 中間層從 HTTP

49、流中提取輸入數(shù)據(jù)，與應(yīng)用程序會(huì)話，并將結(jié)果嵌入到文檔中。向客戶發(fā)送顯式數(shù)據(jù)（即文檔） 3、 向客戶發(fā)送顯式數(shù)據(jù)（即文檔）。這個(gè)文檔可以用各種格式發(fā)送，包括文本（HTML 或 XML），二進(jìn)制（GIF 圖），甚至可以式建立在其他底層格式之上的壓縮格式，如 gzip。但是，到目前為止，HTML 式最常用的格式，故而 servelt 和 JSP 的重要任務(wù)之一就式將結(jié)果包裝到 HTML中。響應(yīng)數(shù)據(jù)。 4、 發(fā)送隱式的 HTTP 響應(yīng)數(shù)據(jù)。發(fā)送的數(shù)據(jù)有兩種：文檔本身，以及后臺(tái)的 HTTP 信息。同樣，兩種數(shù)據(jù)對(duì)開(kāi)發(fā)來(lái)說(shuō)都式至關(guān)重要的。HTTP 響應(yīng)數(shù)據(jù)的發(fā)送過(guò)程涉及告知瀏覽器或其他客戶程序所返回文檔的

50、類型 （如 HTML） ，設(shè)置 cookie 和緩存參數(shù)，以及其他類似的任務(wù)。 1.2 動(dòng)態(tài)構(gòu)建網(wǎng)頁(yè)的原因 預(yù)先建立的文檔可以滿足客戶的許多請(qǐng)求，服務(wù)器無(wú)需調(diào)用 servlet 就可以處理這些請(qǐng)求。然而，許多情況下靜態(tài)的結(jié)果不能滿足要求，我們需要針對(duì)每個(gè)請(qǐng)求生成一個(gè)頁(yè)面。實(shí)時(shí)構(gòu)建頁(yè)面的理由有很多種： 1、網(wǎng)頁(yè)基于客戶發(fā)送的數(shù)據(jù)。網(wǎng)頁(yè)基于客戶發(fā)送的數(shù)據(jù)。例如，搜索引擎生成的頁(yè)面，以及在線商店的訂單確認(rèn)頁(yè)面，都要針對(duì)特定的用戶請(qǐng)求而產(chǎn)生。在沒(méi)有讀取到用戶提交的數(shù)據(jù)之前，我們不知道應(yīng)該顯示什么。要記住，用戶提交兩種類型的數(shù)據(jù)：顯示（即 HTML 表單的數(shù)據(jù)）和隱式（即 HTTP 請(qǐng)求的報(bào)頭）。兩種輸

51、入都可用來(lái)構(gòu)建輸出頁(yè)面?；?cookie 值針對(duì)具體用戶構(gòu)建頁(yè)面的情 況尤其普遍。 2、頁(yè)面由頻繁改變的數(shù)據(jù)導(dǎo)出。 頁(yè)面由頻繁改變的數(shù)據(jù)導(dǎo)出。 如果頁(yè)面需要根據(jù)每個(gè)具體的請(qǐng)求做出相應(yīng)的改變， 當(dāng)然需要在請(qǐng)求發(fā)生時(shí)構(gòu)建響應(yīng)。但是，如果頁(yè)面周期性地改變，我們可以用兩種方式來(lái)處理它：周期性地在服 務(wù)器上構(gòu)建新的頁(yè)面（和客戶請(qǐng)求無(wú)關(guān)） ，或者僅僅在用戶請(qǐng)求該頁(yè)面時(shí)再構(gòu)建。具 體應(yīng)該采用哪種方式要根據(jù)具體情況而定，但后一種方式常常更為方便，因?yàn)樗恍?簡(jiǎn)單地等待用戶的請(qǐng)求。例如，天氣預(yù)報(bào)或新聞網(wǎng)站可能會(huì)動(dòng)態(tài)地構(gòu)建頁(yè)面，也有可 能會(huì)返回之前構(gòu)建的頁(yè)面（如果它還是最新的話） 。 3、頁(yè)面中使用了來(lái)自公司數(shù)

52、據(jù)庫(kù)或其他數(shù)據(jù)庫(kù)斷數(shù)據(jù)源的信息。 頁(yè)面中使用了來(lái)自公司數(shù)據(jù)庫(kù)或其他數(shù)據(jù)庫(kù)斷數(shù)據(jù)源的信息。如果數(shù)據(jù)存儲(chǔ)在數(shù)據(jù)庫(kù)中，那么，即使客戶端使用動(dòng)態(tài) Web 內(nèi)容，比如 applet，我們依舊需要執(zhí)行服務(wù)器端處理。想象以下，如果一個(gè)搜索引擎網(wǎng)站完全使用 applet，那么用戶將會(huì)看到：“正在下載 50TB 的 applet，請(qǐng)等待！”。顯然，這樣 很愚蠢； 這種情況下，我們需要與數(shù)據(jù)庫(kù)進(jìn)行會(huì)話。從客戶端到 Web 層再到數(shù)據(jù)庫(kù) （三 層結(jié)構(gòu)） ，要比從 applet 直接到數(shù)據(jù)庫(kù)（二層結(jié)構(gòu)）更靈活，也更安全，而性能上的 損失很少甚至沒(méi)有。畢竟數(shù)據(jù)庫(kù)調(diào)用通常是對(duì)速度影響最大的步驟，因而，經(jīng)過(guò)中間 層可以執(zhí)行

53、高速緩存和連接共享。理論上講，servelt 并非只用于處理 HTTP 請(qǐng)求的 Web 服務(wù)器或應(yīng)用服務(wù)器，它同樣可以用于其他類型的服務(wù)器。例如，servlet 能夠嵌入到 FTP 或郵件服務(wù)器中，擴(kuò)展他們的功能。而且，用于會(huì)話啟動(dòng)協(xié)議服務(wù)器的servlet API 最近已經(jīng)被標(biāo)準(zhǔn)化（參見(jiàn) /en/jsr/detail?id=116）。但在實(shí)踐中，servelt 的這種用法尚不流行，在此，我們只論述 HTTP Servlet。相對(duì)于“傳統(tǒng)” 1.3 Servlet 相對(duì)于“傳統(tǒng)”CGI 的優(yōu)點(diǎn) 和傳統(tǒng) CGI 及許多類 CGI 技術(shù)相比，Java servelt 效率

54、更高、更易用、更強(qiáng)大、 更容易移植、更安全、也更廉價(jià)。 1、效率 應(yīng)用傳統(tǒng)的 CGI，針對(duì)每個(gè) HTTP 請(qǐng)求都用啟動(dòng)一個(gè)新的進(jìn)程。如果 CGI 程序自身相對(duì)比較簡(jiǎn)短，那么啟動(dòng)進(jìn)程的開(kāi)銷會(huì)占用大部分執(zhí)行時(shí)間。而使用 servelt， Java 虛擬機(jī)會(huì)一直運(yùn)行，并用輕量級(jí)的 Java 線程處理每個(gè)請(qǐng)求，而非重量級(jí)的操作系統(tǒng)進(jìn)程。類似地，應(yīng)用傳統(tǒng)的 CGI 技術(shù)，如果存在對(duì)同一 CGI 程序的 N 個(gè)請(qǐng)求，那么 CGI 程序的代碼會(huì)載入內(nèi)存 N 次。同樣的情況，如果使用 servlet 則啟動(dòng) N 個(gè)線程， 單僅僅載入 servlet 類的單一副本。這種方式減少了服務(wù)器的內(nèi)存需求，通過(guò)實(shí)例化 更

55、少的對(duì)象從而節(jié)省了時(shí)間。最后，當(dāng) CGI 程序結(jié)束對(duì)請(qǐng)求的處理之后，程序結(jié)束。 這種方式難以緩存計(jì)算結(jié)果，保持?jǐn)?shù)據(jù)庫(kù)連接打開(kāi)，或是執(zhí)行依靠持續(xù)性數(shù)據(jù)的其他優(yōu)化。然而，servelt 會(huì)一直停留在內(nèi)存中（即使請(qǐng)求處理完畢），因而可以直接存 儲(chǔ)客戶請(qǐng)求之間的任意復(fù)雜數(shù)據(jù)。 2、便利 Servelt 提供大量的基礎(chǔ)構(gòu)造，可以自動(dòng)分析和解碼 HTML 的表單數(shù)據(jù)，讀取和設(shè)置 HTTP 報(bào)頭，處理 cookie，跟蹤會(huì)話，以及其他次類高級(jí)功能。而在 CGI 中，大 部分工作都需要我們資金完成。另外，如果您已經(jīng)了解了 Java 編程語(yǔ)言，為什么還有學(xué)校 Perl 呢？您已經(jīng)承認(rèn)應(yīng)用 Java 技術(shù)編寫(xiě)的代

56、碼要比 Visual Basic， VBScript 4 或 C編寫(xiě)的代碼更可靠，且更易重用，為什么還有倒退回去選擇那些語(yǔ)言來(lái)開(kāi)發(fā)服務(wù)器端的程序呢？ 3、強(qiáng)大 Servlet 支持常規(guī) CGI 難以實(shí)現(xiàn)或根本不能實(shí)現(xiàn)的幾項(xiàng)功能。Servlet 能夠直接 于 Web 服務(wù)器對(duì)話，而常規(guī)的 CGI 程序做不到這一點(diǎn)，至少在不使用服務(wù)器專有 API 的情況下是這樣。例如，與 Web 服務(wù)器的通信使得講相對(duì) URL 轉(zhuǎn)換成具體的路徑名變 得更為容易。多個(gè) servelt 還可以共享數(shù)據(jù)，從而易于實(shí)現(xiàn)數(shù)據(jù)庫(kù)連接共享和類似的 資源共享優(yōu)化。Servelt 還能維護(hù)請(qǐng)求之間的信息，使得諸如會(huì)話跟蹤和計(jì)算結(jié)果緩 存等技術(shù)變得更為簡(jiǎn)單。 4、可移植性 Servelt 使用 Java 編程語(yǔ)言，并且遵循標(biāo)準(zhǔn)的 API。所有主要的 Web 服務(wù)器。實(shí)際上都直接或通過(guò)插件支持 servlet。因此。為 Macromedia JRun 編寫(xiě)的 servlet，可以不經(jīng)過(guò)任何修改地在 Apache Tomcat，Microsoft Intern