【正文】 這樣，一旦這樣的一個(gè)部件寫好，它可以為多個(gè)程序重復(fù)引用，實(shí)現(xiàn)了程序的可重用性。這樣，一個(gè)熟悉 HTML 網(wǎng)頁編寫的設(shè)計(jì)人員可以很容易進(jìn)行 JSP 網(wǎng)頁的開發(fā)。 （ 5）如果 .jsp 文件被修改了，服務(wù)器將根據(jù)設(shè)置決定是否對該文件重新編譯，如果需要重新編譯，則將編譯結(jié)果取代內(nèi)存中的 Servlet，并繼續(xù)上述處理過程。 （ 2）如果轉(zhuǎn)換成功， JSP 引擎用 javac 把該 Java 源文件編譯成相應(yīng)的 class文件。 希望在 JSP 文檔中導(dǎo)入一段 XML 文件，或?qū)?XML 語法的 JSP 頁面。在這兩種情況下，你可能都希望保證 servlet 或 JSP 可以獨(dú)立于所導(dǎo)入的內(nèi)容進(jìn) 行開發(fā)， servlet或 JSP 的實(shí)現(xiàn)在必要時(shí)正確地更新其導(dǎo)入的內(nèi)容。它可以支持這樣的效果：當(dāng)光標(biāo)在 Web 頁的某個(gè)位置移動時(shí)驗(yàn)證用戶輸入或者變換圖像。在 JSP , 可被描述的唯一事件是初始化和頁的損壞。 JSP對 “glue”動作是一種語言，它是二進(jìn)制。多數(shù)細(xì)節(jié)不是具體語言，這些細(xì)節(jié)在這個(gè)章節(jié)里描述。 能夠快速地開發(fā)和測試。 Servlet 會在本書第 4 章介紹。如果多個(gè)用戶并發(fā)地訪問該程序，這些進(jìn)程將消耗該 Web 服務(wù)器所有的可用資源，并且系統(tǒng)性能會降低到極其低下的地步。 基于瀏覽器客戶端的應(yīng)用程序比傳統(tǒng)的基于客戶機(jī) /服務(wù)器的應(yīng)用程序有幾個(gè)好處。下面就對 JSP 及其相關(guān)技術(shù)進(jìn)行簡單的介紹。t the only dynamic web technology, also not the first one, in the JSP technology existed before the emergence of several excellent dynamic web technology, such as CGI, ASP, etc. With the introduction of these technologies under dynamic web technology, the development and the JSP. Technical JSP the development background and development history In web brief history, from a world wide web that most of the work information static on stock transactions evolution to acquisition of an operation and infrastructure. In a variety of applications, may be used for based on Web client, look no restrictions. Based on the browser client applications than traditional based on client/server applications has several advantages. These benefits include almost no limit client access and extremely simplified application deployment and management (to update an application, management personnel only need to change the program on a server, not thousands of installation in client applications). So, the software industry is rapidly to build on the client browser multilayer application. The rapid growth of exquisite based Web application requirements development of technical improvements. Static HTML to show relatively static content is right choice, The new challenge is to create the interaction based on Web applications, in these procedures, the content of a Web page is based on the user39。s context. Use the c:import The operation principle and the advantages of JSP tags In this section of the operating principle of simple introduction JSP and strengths. For the first time in a JSP documents requested by the engine, JSP Servlet is transformed into a document JSP. This engine is itself a Servlet. The operating process of the JSP shown below: (1) the JSP engine put the JSP files converting a Java source files (Servlet), if you find the files have any grammar mistake JSP, conversion process will interrupt, and to the server and client output error messages. (2) if converted, with the engine JSP javac Java source file piler into a corresponding scaleup files. (3) to create a the Servlet (JSP page), the transformation of the Servlet jspInit () method was executed, jspInit () method in the life cycle of Servlet executed only once. (4) jspService () method invocation to the client requests. For each request, JSP engine to create a new thread for processing the request. If you have multiple clients and request the JSP files, JSP engine will create multiple threads. Each client requests a thread. To execute multithread can greatly reduce the requirement of system resources, improving the concurrency value and response time. But also should notice the multithread programming, due to the limited Servlet always in response to memory, so is very fast. (5) if the file has been modified. The JSP, server will be set according to the document to decide whether to repile, if need to repile, will replace the Servlet pile the memory and continue the process. (6) although the JSP efficiency is high, but at first when the need to convert and pile and some slight delay. In addition, if at any time due to reasons of system resources, JSP engine will in some way of uncertain Servlet will remove from memory. When this happens jspDestroy () method was first call. (7) and then Servlet examples were marked with add garbage collection. But in jspInit () some initialization work, if establish connection with database, or to establish a w