As a point of
reference, the HttpHandler class has similar behavior to ISAPI extensions. Likewise, the HttpModule
class provides similar functionality to ISAPI filters. These two .NET classes greatly expand the
ISAPI library concept, as the classes are fully integrated into the ASP.NET architecture.
CHAPTER 3 ?– A SP.NET S TATE MANAGEMENT 87
Figure 3-2. ASP.NET request processing classes
HttpHandler
HttpHandler objects deserve special attention, because ASP.NET uses this same architecture
to process requests for .aspx and .asmx pages. HttpHandlers enable processing of individual
HTTP URLs or groups of URL extensions within an application. Table 3-1 shows examples of
the HttpHandlers provided in ASP.NET by default.
The ASP.NET page handler PageHandlerFactory performs the important task of receiving
the user request and creating the Page object for manipulation by the developer. The Page object
makes user state easily accessible; this state information includes application and session
state, data stored in ViewState, and data stored in control state, which is new in ASP.NET 2.0
and later.
In general, an HttpHandler can be either synchronous or asynchronous. As you would guess,
a synchronous handler does not return data until it finishes processing the HTTP request for
which it is called.
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