The gain is that you can create web-based integration points by leveraging a native ASP.NET architecture at the same time. This allows you to provide a user-story-based integration routine (ala FaceBook, Twitter) as a wrapper of /or in addition to any service layer integrations that may be exposed.
Here are some points I read from Scott Gu's Blog on the topic. He outlines the highlights and additions to the framework. I think the real excitement is in the realization of the walls that are coming down on platform dependence and ease of developing rich client experiences with web services in a Windows environment.
Our new ASP.NET Web API support enables you to easily create powerful Web APIs that can be accessed from a broad range of clients (ranging from browsers using JavaScript, to native apps on any mobile/client platform). It provides the following support:
- Modern HTTP programming model: Directly access and manipulate HTTP requests and responses in your Web APIs using a clean, strongly typed HTTP object model. In addition to supporting this HTTP programming model on the server, we also support the same programming model on the client with the new HttpClient API that can be used to call Web APIs from any .NET application.
- Content negotiation: Web API has built-in support for content negotiation – which enables the client and server to work together to determine the right format for data being returned from an API. We provide default support for JSON, XML and Form URL-encoded formats, and you can extend this support by adding your own formatters, or even replace the default content negotiation strategy with one of your own.
- Query composition: Web API enables you to easily support querying via the OData URL conventions. When you return a type of IQueryable<T> from your Web API, the framework will automatically provide OData query support over it – making it easy to implement paging and sorting.
- Model binding and validation: Model binders provide an easy way to extract data from various parts of an HTTP request and convert those message parts into .NET objects which can be used by Web API actions. Web API supports the same model binding and validation infrastructure that ASP.NET MVC supports today.
- Routes: Web APIs support the full set of routing capabilities supported within ASP.NET MVC and ASP.NET today, including route parameters and constraints. Web API also provides smart conventions by default, enabling you to easily create classes that implement Web APIs without having to apply attributes to your classes or methods. Web API configuration is accomplished solely through code – leaving your config files clean.
- Filters: Web APIs enables you to easily use and create filters (for example: [authorization]) that enable you to encapsulate and apply cross-cutting behavior.
- Improved testability: Rather than setting HTTP details in static context objects, Web API actions can now work with instances of HttpRequestMessage and HttpResponseMessage – two new HTTP objects that (among other things) make testing much easier. As an example, you can unit test your Web APIs without having to use a Mocking framework.
- IoC Support: Web API supports the service locator pattern implemented by ASP.NET MVC, which enables you to resolve dependencies for many different facilities. You can easily integrate this with an IoC container or dependency injection framework to enable clean resolution of dependencies.
- Flexible Hosting: Web APIs can be hosted within any type of ASP.NET application (including both ASP.NET MVC and ASP.NET Web Forms based applications). We’ve also designed the Web API support so that you can also optionally host/expose them within your own process if you don’t want to use ASP.NET/IIS to do so. This gives you maximum flexibility in how and where you use it.
