摘 要

JSP(JavaServer Pages, java服務(wù)器頁(yè)面)是一種開發(fā)Web應(yīng)用程序的新技術(shù)。自從首次發(fā)布以來，他一直受到密切的關(guān)注。
為什么JSP如此激動(dòng)人心，一個(gè)重要的原因是它是基于Java的，而Java極為適合于干企業(yè)級(jí)計(jì)算。事實(shí)上JSP是J2EE平臺(tái)的關(guān)鍵部分，她能夠利用Java企業(yè)級(jí)類庫(kù)的許多優(yōu)點(diǎn)，比如說JDBC，EJB和JNDI。另一個(gè)原因在于JSP支持強(qiáng)大的WEB應(yīng)用程序開發(fā)模式，它能夠把外觀呈現(xiàn)與處理過程分離開來。要理解為什么這個(gè)特性如此的重要，我們需要了解一點(diǎn)WEB的發(fā)展歷史。在WEB發(fā)展的早期，開發(fā)動(dòng)態(tài)網(wǎng)頁(yè)的唯一工具是CGI。CGI描述了WEB服務(wù)器如何使某個(gè)程序接收用戶的輸入，以及該程序如何向WEB服務(wù)器提供動(dòng)態(tài)生成的內(nèi)容作為反饋。CGI腳本常用Perl語言來編寫（事實(shí)上，CGI Perl腳本現(xiàn)在仍在許多動(dòng)態(tài)網(wǎng)站上運(yùn)行著）。然而，CGI并非一種高效率的解決方案。對(duì)于每一個(gè)請(qǐng)求，WEB服務(wù)器都要?jiǎng)?chuàng)建一個(gè)新的操作系統(tǒng)進(jìn)程，裝入一個(gè)Perl解釋器和Perl腳本，運(yùn)行該腳本，然后當(dāng)一切完成后，再釋放該進(jìn)程。
在最近幾年里，為了提供更加有效的解決方案，許多CGI的替代品進(jìn)入了程序員的工具箱，例如，F(xiàn)astCGI，在外部永久進(jìn)程（或進(jìn)程池中）運(yùn)行每一個(gè)CGI程序。另外，用于APACHE服務(wù)器的mod_perl等，都是在WEB服務(wù)器的同一進(jìn)程中運(yùn)行服務(wù)器端程序的方案。雖然這些解決方案提供了更好的性能和可伸縮性。但他們中的每一種都只能被幾種常用的Web服務(wù)器所支持。
1997年提出的Java Servlet API提供了一種新的解決辦法。然而，所有這些技術(shù)都面臨著同一個(gè)問題：嵌入到程序中的HTML代碼。如果你閱讀過Servlet代碼，你就會(huì)發(fā)現(xiàn)有數(shù)不清的對(duì)Out.Println()的調(diào)用，這些調(diào)用是為了輸出HTML的標(biāo)記。對(duì)于一個(gè)在簡(jiǎn)單站點(diǎn)上工作的個(gè)人開發(fā)者來說，這種方式很合適，但當(dāng)有幾個(gè)擁有不同技能的人協(xié)同開發(fā)WEB應(yīng)用程序時(shí)，這就變得極為艱難了。這個(gè)問題已經(jīng)成為當(dāng)務(wù)之急。當(dāng)網(wǎng)站變得越來越復(fù)雜，并越來越多的依靠良好的協(xié)同組織的時(shí)候，web界面的美觀性和易用性就變成了最重要的東西。
Java服務(wù)器頁(yè)面提供的正是這樣一種開發(fā)模式。它使得擅長(zhǎng)圖形制作，布局和可用性的網(wǎng)頁(yè)設(shè)計(jì)師與精通服務(wù)器端技術(shù)（例如多線程，資源池，數(shù)據(jù)庫(kù)和高速緩存）的程序員能夠協(xié)同工作。盡管其他的一些技術(shù)也支持類似的開發(fā)模式，例如ASP，PHP和ColdFusion，但他們當(dāng)中沒有一個(gè)能夠提供JSP的所有優(yōu)點(diǎn)。


Abstract
JavaServer Pages (JSP) is a technology for web application development that has received a great deal of attention since it was first announced in 1999. Since then, it has gone through two revisions.
Why is JSP so exciting? One reason is that JSP is Java-based, and Java is well suited for enterprise computing. In fact, JSP is a key part of the Java 2 Enterprise Edition (J2EE) platform and can take advantage of the many Java Enterprise libraries, such as JDBC ,JNDI , and Enterprise JavaBeans .
Another reason is that JSP supports a powerful model for developing web applications that separates presentation from processing. Understanding why this is so important requires a bit of a history lesson. In the early days of the Web, the only tool for developing dynamic web content was the Common Gateway Interface (CGI). CGI outlined how a web server made user input available to a program, as well as how the program provided the web server with dynamically generated content to send back. CGI scripts were typically written in Perl. (In fact, Perl/CGI scripts still drive numerous dynamic web sites.) However, CGI is not an efficient solution. For every request, the web server has to create a new operating-system process, load a Perl interpreter and the Perl script, execute the script, and then dispose of it when it's done.
To provide a more efficient solution, various alternatives to CGI have been added to programmers' toolboxes over the last few years: FastCGI, for example, runs each CGI program in an external permanent process (or a pool of processes). In addition, mod_perl for Apache, and ISAPI for Microsoft's IIS all run server-side programs in the same process as the web server itself. While these solutions offer better performance and scalability, each one is supported only by a subset of the popular web servers.
The Java Servlet API, introduced in early 1997, provides a solution to the portability issue.However, all these technologies suffer from a common problem: HTML code embedded inside programs. If you've ever looked at the code for a servlet, you've probably seen endless calls to out.println( ) that contain scores of HTML tags. For the individual developer working on a simple web site, this approach may work fine, but it makes it difficult for people with different skills to work together to develop a web application.
This embedded HTML code is becoming a significant problem. As web sites become increasingly complex and more critical to an organization's success, the appearance and usability of the web interface becomes paramount.
JSP provides just such a development model, allowing web-page authors with skills in areas such as client-side technologies and usability, to work in tandem with programmers who are experienced in server-side technologies, such as multithreading, resource pooling, databases, and caching. While there are other technologies, such as ASP, PHP, and ColdFusion, that support similar development models, none offer all the advantages of JSP.


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