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ColdFusion 10: HTTP Content Negotiation + REST– Part 2

Following with my previous post on how content negotiation between the client and server help in invoking an appropriate REST service. In this post I’ll explain how one can specify multiple mime types in the request header and also the quality factor that enables server to decide which mime type to serve for the incoming request. The client sends a HTTP request to the Server along with several headers, one of them is the Accept header. The Accept header can contain a list of mime types that the client (user agent) is willing to process. These mime types are separated by a comma and may optionally be combined with the quality factor.

A CFC can contain several methods with produces attribute set to a specific mime type. The Accept header may contain several mime types:

text/html, text/plain, application/xml, application/json, */*

Server would parse the Accept header and will search for a REST service that matches the mime type specified first in the Accept header list. In this case ‘text/html’, if the same is not found then the next one in the list – text/plain. The client would specify the order of preference in the Accept header.

The Accept header can also specify the quality factory along with the mime types which defines relative degree of preference between different mime types. Here the header will be of the form:

text/html;q=0.7, text/plain;q=0.8, application/xml;q=0.9

Here the preference for each of the mime types is specified as quality factor in the header. The method with produces attribute set to ‘application/xml’ would be invoked because its quality factor – 0.9 is higher than the other mime types. By default the quality factory is 1 and it can have values between 0 and 1.

A REST request can also be sent through a browser by providing the URI in the address bar. Here the browser would send the default Accept header and an appropriate REST service would be invoked. Therefore if you try to send the same request from two different browsers, it would return different results.

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