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Play API REST Template [Play 2.5 - Scala]

Template to show how to implement an API using Play Framework.

There is another companion project to test this template here.

Note: All this information is also available as a tutorial if you run the app using Activator UI.

The characteristics and objectives of this template are:

What this template does NOT explain:

Please, read this interesting post: Best Practices for Designing a Pragmatic RESTful API (also in Spanish).

First of all, this is a template, not a library. It simply tries to give you some clues to develop your own API. So copy the files you need, adapt them to your code and play with it.

And please, don't forget starring this project if you consider it has been useful for you.

Also check my other projects:

Preview

The main idea is to simplify the code for a common API. Let's see a preview example. Imagine you have a list of "todo" tasks. And only for logged users.

conf/routes

GET         /tasks            controllers.Tasks.list(q: Option[String], done: Option[Boolean], sort: Option[String], page: Int ?= 1, size: Int ?= 10)
GET         /tasks/:id        controllers.Tasks.info(id: Long)
PUT         /tasks/:id        controllers.Tasks.update(id: Long)
DELETE      /tasks/:id        controllers.Tasks.delete(id: Long)

Note you can paginate, filter, search and sort your lists:

/tasks?size=20&page=3
/tasks?q=blah&done=true
/tasks?sort=-deadline,-date,order

app/controllers/Tasks.scala

class Tasks @Inject() (val messagesApi: MessagesApi) extends api.ApiController {

  // Returns a 'page' of tasks with searching, filtering, sorting and pagination
  def list(q: Option[String], done: Option[Boolean], sort: Option[String], p: Int, s: Int) = SecuredApiAction { implicit request =>
    sortedPage(sort, Task.sortingFields, default = "order") { sortingFields =>
      Task.page(q, done, sortingFields, p, s)
    }
  }

  // Returns a tasks or an 'ItemNotFound' error
  def info(id: Long) = SecuredApiAction { implicit request =>
    maybeItem(Task.findById(id))
  }

  // Updates a task
  def update(id: Long) = SecuredApiActionWithBody { implicit request =>
    readFromRequest[Task] { task =>
      Task.basicUpdate(id, task.text, task.deadline).flatMap { isOk =>
        if (isOk) noContent() else errorInternal
      }
    }
  }

  // Deletes a task
  def delete(id: Long) = SecuredApiAction { implicit request =>
    Task.delete(id).flatMap { _ =>
      noContent()
    }
  }
}

Let's see how to get this.

Basic structure

It's simple. In Play you have the classes Controller, Action[A], Request[A] and Result. With this template we have their equivalences:

Api

Object that contains common values and methods.

ApiRequest[A] and SecuredApiRequest[A]

Every request should have the following headers:

ApiRequest[A] it's a simple RequestWrapper[A] with several additional values:

SecuredApiRequest[A] extends from ApiRequest[A] and it's used for secured requests where the user must be signed in.

UserAwareApiRequest[A] can be used when user authentication is optional. It extends from ApiRequest[A] add the following fields:

ApiResult

It's a trait that stores the information required to create a Result. It stores the Status Code, the JSON value and the headers for the response.

ApiResponse

It extends from ApiResult and it represents a successful response for the request. The available Status Codes are: STATUS_OK, STATUS_CREATED, STATUS_ACCEPTED and STATUS_NOCONTENT. And it provides the following factory methods:

ok(json: JsValue, headers: (String, String)*)
ok[A](json: JsValue, page: Page[A], headers: (String, String)*)
created(json: JsValue, headers: (String, String)*)
created(headers: (String, String)*)
accepted(json: JsValue, headers: (String, String)*)
accepted(headers: (String, String)*)
noContent(headers: (String, String)*)

ApiError

It extends from ApiResult and it represents an error response for the request. It stores a specific error code, a descriptive message and an optional additional object with more information. The JSON structure is the like the following:

{ "code": 400, "msg": "Bad Request" }

or

{ "code": 125, "msg": "Malformed body", "info": "additional information about the error" }

The available Status Codes are: STATUS_BADREQUEST, STATUS_UNAUTHORIZED, STATUS_FORBIDDEN, STATUS_NOTFOUND and STATUS_INTERNAL_SERVER. And it provides a list of predefined code errors and their corresponding factory methods.

ApiController

It's simply a trait that extends from Controller and adds a set of utilities to do the life easier.

Actions

There are a list of useful actions for each request method:

ApiAction(action: ApiRequest[Unit] => Future[ApiResult])
ApiActionWithBody(action: ApiRequest[JsValue] => Future[ApiResult])

And their equivalences for secured requests (and optional ones):

SecuredApiAction(action: SecuredApiRequest[Unit] => Future[ApiResult])
SecuredApiActionWithBody(action: SecuredApiRequest[JsValue] => Future[ApiResult])

UserAwareApiAction(action: UserAwareApiRequest[Unit] => Future[ApiResult])
UserAwareApiActionWithBody(action: UserAwareApiRequest[JsValue] => Future[ApiResult])

Creating ApiResults from writable JSON objects

There are a set of useful methods to create ApiResults from JSON objects:

ok[A](obj: A, headers: (String, String)*)(implicit w: Writes[A]): Future[ApiResult]
ok[A](futObj: Future[A], headers: (String, String)*)(implicit w: Writes[A]): Future[ApiResult]
maybeItem[A](opt: Option[A], headers: (String, String)*)(implicit w: Writes[A], req: RequestHeader): Future[ApiResult]
maybeItem[A](futOpt: Future[Option[A]], headers: (String, String)*)(implicit w: Writes[A], req: RequestHeader): Future[ApiResult]
page[A](p: Page[A], headers: (String, String)*)(implicit w: Writes[A]): Future[ApiResult]
page[A](futP: Future[Page[A]], headers: (String, String)*)(implicit w: Writes[A]): Future[ApiResult]
created[A](obj: A, headers: (String, String)*)(implicit w: Writes[A]): Future[ApiResult]
created[A](futObj: Future[A], headers: (String, String)*)(implicit w: Writes[A]): Future[ApiResult]
created(headers: (String, String)*): Future[ApiResult]
accepted[A](obj: A, headers: (String, String)*)(implicit w: Writes[A]): Future[ApiResult]
accepted[A](futObj: Future[A], headers: (String, String)*)(implicit w: Writes[A]): Future[ApiResult]
accepted(headers: (String, String)*): Future[ApiResult]
noContent(headers: (String, String)*): Future[ApiResult]

Pagination

There is a simple class to hold the pagination information:

case class Page[+A](items: Seq[A], page: Int, size: Int, total: Long) {
  def offset = (page - 1) * size + 1
}

Then, we need to create a Page class with our list of items and simply call the page() method ofApiController.

val itemsPage: Future[Page[Item]] = ...
itemsPage.map(page(_))

or simply:

page(itemsPage)

It will add automatically the following headers to the response:

Filtering, searching and sorting

Filtering and searching are very straightforward. Imagine you have an action to list the tasks in a TO-DO list. If you would like to add the ability to filter those that are done or not, or to seach for a specific query term, you only have to add this parameters and handle them to implement them within your search engine.

/tasks?q=blah&done=true
# Route
GET    /tasks  controllers.Tasks.list(q: Option[String], done: Option[Boolean])

However, sorting is trickier. Let's see this example:

/tasks?sort=-deadline,-date,order
# Route
GET    /tasks  controllers.Tasks.list(sort: Option[String])

The sort parameter have a comma separated list of signed fields, ordered by priority. So for the example, you would like to order by deadline in descendent order, then by date in descendent order, and finally by the task's order within the list in ascendent order. To make it a bit easier, ApiController defines the following method

processSortByParam(
  sortBy: Option[String], 
  allowedFields: Seq[String], 
  default: String): Either[ApiError, Seq[(String, Boolean)]]

It takes the sort parameter, a list of available allowed fields to sort by, and a default sorting string. Then it returns a list of pairs (String, Boolean) with the corresponding field and order (true if it's descendent), or an ApiError if any of the field is not allowed.

Then, you can implement the sorting as you want from this Seq[(field, order)], depending on your DB storage.

Envelope

There are cases where an API client can't access to the HTTP Headers. For that cases you can add the parameter envelope=true to the query and it will encapsulate the data information and the headers within a JSON object like that:

{ "data": "your-json-response", "status": "status-code", "headers": { "header1": "value1", "header2": "value2" } }

How to use it: a simple TODO list example

This template has implemented a basic TODO example, so you can check it. But here let's see some examples.

Your controllers should extend ApiController and I18nSupport.

class Tasks @Inject() (val messagesApi: MessagesApi) extends api.ApiController { … }

To list the tasks and allow searching, filtering, sorting and pagination:

def list(folderId: Long, q: Option[String], done: Option[Boolean], sort: Option[String], p: Int, s: Int) = 
  SecuredApiAction { implicit request =>
    sortedPage(sort, Task.sortingFields, default = "order") { sortingFields =>
      Task.page(folderId, q, done, sortingFields, p, s)
    }
  }

Where Task.page(…) implements the functionality to return a Page[Task] with the corresponding tasks applying this parameters.

To insert new items, there is another method in ApiController that reads a writable object and returns an ApiError if needed.

def insert(folderId: Long) = SecuredApiActionWithBody { implicit request =>
  readFromRequest[Task] { task =>
    Task.insert(folderId, task.text, new Date(), task.deadline).flatMap {
      case (id, newTask) => created(newTask)
    }
  }
}

It would return the new created task within the body response. But if you would like to return an empty body you may want to add a Location header with the created URI:

created(Api.locationHeader(routes.Tasks.info(id)))

To return a single item, update it and delete it:

def info(id: Long) = SecuredApiAction { implicit request =>
  maybeItem(Task.findById(id))
}

def update(id: Long) = SecuredApiActionWithBody { implicit request =>
  readFromRequest[Task] { task =>
    Task.basicUpdate(id, task.text, task.deadline).flatMap { isOk =>
      if (isOk) noContent() else errorInternal
    }
  }
}

def delete(id: Long) = SecuredApiAction { implicit request =>
  Task.delete(id).flatMap { _ => noContent() }
}

The authorization based on the Auth Token is done within the Auth controller. It handles the sign in and sign out actions to handle the tokens, and sign up one to register a new user.

FakeDB

For the example, a fake DB is implemented. The implementation is not relevant, but you can check all the information within the DB in your browser at /fakeDB. That will let you check what's happening while you're testing with the tester.

Test Units

Although there is a companion tester project, don't forget to use unit testing for production. You can see some examples in this template.