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1、 毕业设计英文资料翻译TOPIC An Overview of Servlet and JSP Technology 题 目 Servlet和JSP技术简述 作 者 相 凤 珍 届 别 2009 届 系 别 计算机与信息工程系 专 业 通信工程 指导教师 胡 虚 怀 职 称 教 授 完成时间 2009年5月20日 An Overview of Servlet and JSP TechnologyGildas Avoine and Philippe OechslinEPFL, Lausanne, Switzerland1.1 A Servlets JobServlets are Java pro
2、grams that run on Web or application servers, acting as a middle layer between requests coming from Web browsers or other clients and databases or applications on the server. Their job is to perform the following tasks, as illustrated in Figure 1-1.Figure 1-11Read the explicit data sent by the clien
3、t.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 client program.2Read the implicit request data sent by the browser.Figure 1-1 shows a single arrow going from the client to the Web server (the layer where servlets an
4、d 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 information. Both varieties are critical. The information includes cookies, information about media types and compression schemes the browser understands, and so
5、 on.3Generate 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 database probably doesnt speak or return results in HTML, so the Web brow
6、ser cant 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 incoming data from the stream, talk to the application, and embed the results inside a
7、 document.4Send the explicit data (i.e., the document) to the client.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 far the most common
8、 format, so an important servlet/JSP task is to wrap the results inside of HTML.5Send the implicit 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 document itself and the behi
9、nd-the-scenes information. Again, both varieties are critical to effective development. Sending 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 tasks. 1.2 Why Build Web Pages Dynam
10、ically?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 number of reasons why Web pages need to
11、be built on-the-fly:1 The 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 dont know what to display until you read the data that the user submits. Just remember
12、 that the user submits two kinds of data: explicit (i.e., HTML form data) and implicit (i.e., 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 value.2The Web page is derived from data that c
13、hanges 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 (independently of client requests), or you could wait
14、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 dynamically, perhaps returning a previously buil
15、t page if that page is still up to date.3The Web page uses information from corporate databases or other server-side sources.If the information is in a database, you need server-side processing even if the client is using dynamic Web content such as an applet. Imagine 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 database. Going from the client to the Web tier to the database (a
