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Catalog / Play Framework Cheat Sheet

Play Framework Cheat Sheet

A concise cheat sheet for the Play Framework, covering essential concepts, configurations, routing, controllers, views, and testing.

Core Concepts & Setup

Project Setup

Create a new Play project using the command-line:

 sbt new playframework/play-scala-seed.g8

or

 sbt new playframework/play-java-seed.g8

Navigate to the project directory:

cd <project-name>

Run the Play application in development mode:

sbt run

Directory Structure

app/

Contains core application code like controllers, models, services.

conf/

Configuration files, including application.conf (main configuration) and routes (route definitions).

public/

Static assets like CSS, JavaScript, and images.

test/

Unit and integration tests.

build.sbt

SBT build definition file.

Configuration (application.conf)

The application.conf file is the primary configuration file. It uses the HOCON format.

play.application.name="my-app"
play.http.secret.key="changeme"

db.default.driver=org.h2.Driver
db.default.url="jdbc:h2:mem:play"

Routing

Routes File

The routes file defines how URLs are mapped to controller actions.

# Routes
# This file defines all application routes (Higher priority routes first)
# ~~~~~

# An example: 
GET   /clients/:id          controllers.Clients.show(id: Long)

Basic Route Syntax

GET /path controllers.MyController.action

Maps a GET request to /path to MyController.action().

POST /submit controllers.MyController.submit

Maps a POST request to /submit to MyController.submit().

* /assets controllers.Assets.versioned(path="/public", file:Asset)

Serves static assets.

Route Parameters

/:id

Simple path segment parameter.

/<id:Int>

Path segment parameter with type (Int, Long, UUID, etc.).

?name=value

Query string parameter.

Controllers

Controller Basics (Scala)

A simple Scala controller:

package controllers

import play.api.mvc._

import javax.inject._

@Singleton
class HomeController @Inject()(val controllerComponents: ControllerComponents) extends BaseController {
  def index() = Action { implicit request: Request[AnyContent] =>
    Ok("Hello, Play!")
  }
}

Dependency Injection: Play uses constructor injection. The @Inject annotation and Singleton ensure the controller is created only once.

Controller Basics (Java)

A simple Java controller:

package controllers;

import play.mvc.*;

import javax.inject.Inject;

public class HomeController extends Controller {
  public Result index() {
    return ok("Hello, Play!");
  }
}

Dependency Injection: Play uses constructor injection. Annotate the constructor with @Inject.

Actions and Results

Action

Represents a unit of work to be performed for an incoming request.

Result

Represents the outcome of an action, typically an HTTP response.

Ok(content)

Returns a 200 OK response with the given content.

BadRequest(content)

Returns a 400 Bad Request response.

Redirect(url)

Returns a 303 See Other redirect to the given URL.

Views and Templates

Templates (Twirl)

Play uses Twirl as its default template engine. Templates are located in the views directory and have a .scala.html extension.

@(message: String)

<h1>@message</h1>

Passing Data to Templates

In a controller (Scala):

Ok(views.html.index("Hello, Play!"))

Passes the string “Hello, Play!” to the index.scala.html template.

In a controller (Java):

return ok(views.html.index.render("Hello, Play!"));

Passes the string “Hello, Play!” to the index.scala.html template.

Template Directives

@

Used to introduce Scala expressions in a template.

@()

Used to define template parameters.

@for(item <- items) { ... }

Looping.

@if(condition) { ... } else { ... }

Conditional statements.

@defining(value) { ... }

Define local variables.
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