问题
Simple task like make AJAX request , pass one parameter and return result, can be done with Web Service and IHttpHandler, so where is the difference ?
回答1:
ASP.NET web services are in fact a type of HttpHandler that provide an XML based communication infrastructure based on W3C standards (SOAP/WSDL). This means that non .NET clients can interoperate with ASP.NET web services. In your case where you're making a very simple single ajax request to return a simple result, ASP.NET/XML web services may be overkill.
It may be more beneficial/efficient to implement a simple custom HttpHandler rather than invoking all of the plumbing and overhead associated with ASP.NET web services. With a custom HttpHandler you can just send the parameter you need and return exactly the result you want to see without any of the supporting SOAP xml that would be created when using XML web services.
来源：https://stackoverflow.com/questions/495344/difference-asp-net-web-service-and-ihttphandler