Building better APIs with Play!

Mar 4 2014

This is the technical companion to my post, Building better APIs with Play!. Herein lies coding examples galore!

RESTful Architecture - Routing

The routes file of a Play app allows you to define the HTTP verb, the route path/pattern, and the corresponding method from the controller. In addition to denoting basic path variables, you can also use regular expressions to match on specific routes (i.e. xml or html formats for example). What’s great about this approach is this file is compiled along with the source code, so any mistakes like an incorrect controller method or invalid HTTP verb will be caught and thrown at compile time.

Action composition

We define two types of custom actions: atomic and composed. Atomic actions can be used stand-alone or as building blocks to be composed with other actions. We use the following pattern for building an atomic action.

The object allows us to use the action by itself, and the case class allows us to compose this action with other actions.

A composed action is strictly syntactic sugar, making it more convenient to combine behaviors and keeping the controller code more concise. We define composed actions using just an object.


Filters are handy for cross-cutting concerns. We’ve had one use case where it was necessary to modify every JSON response with links to metadata. We achieved this using a filter and the Play Enumeratee library

JSON - Global messaging

Building an effective API requires being responsive to users in a comprehensive manner. All concievable events should be handled appropriately, such as incorrect requests from the client or internal server errors. Creating a Global object allows you to generically craft responses to handle these situations. We define methods to handle events like internal errors, route not found, or a bad request.


Play is well-equipped to handle the nuances of API development and maintenance. We’re pleased with the stability and performance we’ve seen thus far and are looking forward to continuing down this path of reactive goodness.

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