【正文】 ata between client requests. 2． Convenient 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 highlevel utilities. In CGI, you have to do much of this yourself. Besides, if you already know the Java programming language, why learn Perl too? You39。然而，數(shù)據(jù)還有可能來自 applet 或定制的 HTTP 客戶程 序。該數(shù)據(jù)庫可能不理解 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)庫進(jìn)行會話。 圖 中顯示了一條從 Web 中間層到客戶端的單箭頭。在沒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。例如，天氣預(yù)報或新聞網(wǎng)站可能會動態(tài)地構(gòu)建頁面，也有可能會返回之前構(gòu)建的頁面（如果它還是最新的話）。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。這種方式減少了服務(wù)器的內(nèi)存需求，通過實(shí)例化更少的對象從而節(jié)省了時間。例如，與 Web 服務(wù)器的通信使得講相對 URL 轉(zhuǎn)換成具體的路徑名變得更為容易。 iPla Enterprise Server。印度接近列表的頂端，可能僅次于美國。他們的 servelt 和 jsp 不需要重寫編寫。他們還是不需要做出任何更改。即使 servelt 執(zhí)行系統(tǒng)調(diào)用激活本地操作系統(tǒng)上的程序，它也不會用到外殼來完成這項任務(wù)。 。 主流 雖然存在許多很好的技術(shù)，但是，如果提供商助支持他們，或開發(fā)人員不知道如何使用這些技術(shù)， 那么它們的優(yōu)點(diǎn)又如何體現(xiàn)呢？ servelt 和 jsp 技術(shù)得到服務(wù)器提供商的廣泛支持，包括 Apache， Oracle， IBM， Sybase， BEA， Maromedia，Causho， Sun/iPla， New Atlanta， ATG， Fujitsu， Lutris， Silverstream， World Wide Web Consortinrm ，以及其他服務(wù)器。因此 ,CGI 程序必須仔細(xì)地過濾掉那些可能被外殼特殊處理的字符，如反引導(dǎo)和分號。沒有問題：他們可以轉(zhuǎn)而使用 Macromedia JRun Professional，該服務(wù)器支持分布式應(yīng)用。 那么，為什么印度和菲律賓都對這項技術(shù)著呢感興趣呢？我們推測答案可能分兩部分。他們是 java2 平臺企業(yè)版的一部分，所以對 servlet 的支持越來越普遍。 Servelt 還能維護(hù)請求之間的信息 ，使得諸如會話跟蹤和計算結(jié)果緩存等技術(shù)變得更為簡單。這種方式難以緩存計算結(jié)果，保持?jǐn)?shù)據(jù)庫連接打開，或是執(zhí)行依靠持續(xù)性數(shù)據(jù)的其他優(yōu)化。 Servlet 相對于 “ 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 效率更高、更易用、更強(qiáng)大、更容易移植、更安全、也更廉價。 如果數(shù)據(jù)存儲在數(shù)據(jù)庫中，那么，即使客戶端使用動態(tài) Web 內(nèi)容，比如applet，我們依舊需要執(zhí)行服務(wù)器端處理。兩種輸入都可用來構(gòu)建輸出頁面。同樣，兩種數(shù)據(jù)對開發(fā)來說都式至關(guān)重要的。對應(yīng)大多數(shù)其他應(yīng)用程序，也存在類似的問題。 圖 中顯示了一條從客戶端到 Web 服務(wù)器的單箭頭，但實(shí)際上從客戶端傳送到 Web 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)，以及后臺的 HTTP 信息。 see so industry support for servlets is being even more pervasive. 5． Inexpensive A number of free or very inexpensive Web servers are good for development use or deployment of low or mediumvolume Web sites. Thus, with servlets and JSP you can start with a free or inexpensive server and migrate to more expensive servers with highperformance 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 connected. For example, Marty tries to keep track of the countries of readers that send him questions by . India was near the top of the list, probably 2 behind the . Marty also taught one of his JSP and servlet training courses (see in Manila, and there was great interest in servlet and JSP 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 welleducated software developers. Second, both countries have (or had, at that time) highly unfavorable currency exchange rates against the . dollar. So, buying a specialpurpose Web server from a . pany consumed a large part of early project funds. 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 the project starts to bee 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 bees even larger, they might want to move to a distributed (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 bees quite large and ple