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1、原文1A low-level Look at the ASP.NET ArchitectureAbstractASP.NET is a powerful platform for building Web applications that provides a tremendous amount of flexibility and power for building just about any kind of Web application. Most people are familiar only with the high level frameworks like WebFor
2、ms and WebServices which sit at the very top level of the ASP.NET hierarchy. In this article Ill describe the lower level aspects of ASP.NET and explain how requests move from Web Server to the ASP.NET runtime and then through the ASP.NET Http Pipeline to process requests. What is ASP.NETLets start
3、with a simple definition: What is ASP.NET? I like to define ASP.NET as follows:ASP.NET is a sophisticated engine using Managed Code for front to back processing of Web Requests.Its much more than just WebForms and Web ServicesASP.NET is a request processing engine. It takes an incoming request and p
4、asses it through its internal pipeline to an end point where you as a developer can attach code to process that request. This engine is actually completely separated from HTTP or the Web Server. In fact, the HTTP Runtime is a component that you can host in your own applications outside of IIS or any
5、 server side application altogether. The runtime provides a complex yet very elegant mechanism for routing requests through this pipeline. There are a number of interrelated objects, most of which are extensible either via subclassing or through event interfaces at almost every level of the process,
6、 so the framework is highly extensible. Through this mechanism its possible to hook into very low level interfaces such as the caching, authentication and authorization. You can even filter content by pre or post processing requests or simply route incoming requests that match a specific signature d
7、irectly to your code or another URL. There are a lot of different ways to accomplish the same thing, but all of the approaches are straightforward to implement, yet provide flexibility in finding the best match for performance and ease of development.The entire ASP.NET engine was completely built in
8、 managed code and all of the extensibility functionality is provided via managed code extensions. This is a testament to the power of the .NET framework in its ability to build sophisticated and very performance oriented architectures. Above all though, the most impressive part of ASP.NET is the tho
9、ughtful design that makes the architecture easy to work with, yet provides hooks into just about any part of the request processing.With ASP.NET you can perform tasks that previously were the domain of ISAPI extensions and filters on IIS with some limitations, but its a lot closer than say ASP was.
10、ISAPI is a low level Win32 style API that had a very meager interface and was very difficult to work for sophisticated applications. Since ISAPI is very low level it also is very fast, but fairly unmanageable for application level development. So, ISAPI has been mainly relegated for some time to pro
11、viding bridge interfaces to other application or platforms. But ISAPI isnt dead by any means. In fact, ASP.NET on Microsoft platforms interfaces with IIS through an ISAPI extension that hosts .NET and through it the ASP.NET runtime. ISAPI provides the core interface from the Web Server and ASP.NET u
12、ses the unmanaged ISAPI code to retrieve input and send output back to the client. The content that ISAPI provides is available via common objects like HttpRequest and HttpResponse that expose the unmanaged data as managed objects with a nice and accessible interface.The ISAPI ConnectionISAPI is a l
13、ow level unmanged Win32 API. The interfaces defined by the ISAPI spec are very simplistic and optimized for performance. They are very low level dealing with raw pointers and function pointer tables for callbacks - but they provide he lowest and most performance oriented interface that developers an
14、d tool vendors can use to hook into IIS. Because ISAPI is very low level its not well suited for building application level code, and ISAPI tends to be used primarily as a bridge interface to provide Application Server type functionality to higher level tools. For example, ASP and ASP.NET both are l
15、ayered on top of ISAPI as is Cold Fusion, most Perl, PHP and JSP implementations running on IIS as well as many third party solutions such as my own Web Connection framework for Visual FoxPro. ISAPI is an excellent tool to provide the high performance plumbing interface to higher level applications,
16、 which can then abstract the information that ISAPI provides. In ASP and ASP.NET, the engines abstract the information provided by the ISAPI interface in the form of objects like Request and Response that read their content out of the ISAPI request information. Think of ISAPI as the plumbing. For ASP.NET the ISAPI dll is very lean and acts merely as a routing mechanism to pipe the inbound request into the ASP.NET runtime. All the heavy lifting and processing,
