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REST is not really a technology in itself, but more an architectural pattern. REST is very simple and just involves using plain XML or JSON as a communication medium, combined with URL patterns that are "representational" of the underlying system, and HTTP methods such as GET, PUT, POST and DELETE.

Each HTTP method maps to an action type. For example GET for retrieving data, POST for creating data, PUT for updating and so on.

Grails includes flexible features that make it easy to create RESTful APIs. Creating a RESTful resource can be as simple as one line of code, as demonstrated in the next section.