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2025-01-27 03:36本頁(yè)面
【正文】 ontrols. As you will see, provides a number of new web controls, a new “master page”model, and various customization techniques. The Role of HTTP Web applications are very different animals from traditional desktop applications (to say the least).The first obvious difference is that a productionlevel web application will always involve at least two worked machines (of course, during development it is entirely possible to have a single machine play the role of both client and server). Given this fact, the machines in question must agree upon a particular wire protocol to determine how to send and receive data. The wire protocol that connects the puters in question is the Hypertext Transfer Protocol (HTTP). When a client machine launches a web browser (such as Netscape Navigator, Mozilla Firefox,or Microsoft Inter Explorer), an HTTP request is made to access a particular resource (such as an *.aspx or *.htm file) on the remote server machine. HTTP is a textbased protocol that is built upon a standard request/response paradigm. For example, if you navigate to . , the browser software leverages a web technology termed Domain Name Service (DNS) that converts the registered URL into a fourpart, 32bit numerical value (aka an IP address). At this point, the browser opens a socket connection (typically via port 80) and sends the HTTP request for the default page at the website. Once the hosting web server receives the ining HTTP request, the specified resource may contain logic that scrapes out any clientsupplied input values (such as values within a text box) in order to format a proper HTTP response. Web programmers may leverage any number of technologies (CGI, ASP, , Java servlets, etc.) to dynamically generate the content to be emitted into the HTTP response. At this point, the clientside browser renders the HTML emitted from the web server. Another aspect of web development that is markedly different from traditional desktop programming is the fact that HTTP is an essentially stateless wire protocol. As soon as the web server emits a response to the client, everything about the previous interaction is fotten. Therefore, as a web developer, it is up to you take specific steps to “remember” information (such as items in a shopping cart) about the clients who are currently logged on to your site. As you will see in the next chapter, provides numerous ways to handle state, many of which are monplace to any web platform (session variables, cookies, and application variables) as well as some new techniques (view state, control state, and the cache). Understanding Web Applications and Web Servers A web application can be understood as a collection of files (*.htm, *.asp, *.aspx, image files, etc.) and related ponents (such as a .NET code library) stored within a particular set of directories on a given web server. As shown in Chapter 24, web applications have a specific life cycle and provide numerous
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