Scala Play from scratch

If DropWizard excels at RESTful webservices, then the Play Framework is often the counterpart which provides an HTML front-end. Although it’s got both Java and Scala support, the Scala support seems to be more active. Here’s an introduction without using all the Activator Framework / play create app template commands.

First, create a directory to work in

$ mkdir LearnPlay
$ cd LearnPlay

Next, you’ll need SBT (the build tool). Here we’re using the latest version (0.13.7). Follow the instructions to save it to the root of your working folder, alongside an SBT shell script to launch it:-

$ wget https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/sbt-launch/0.13.7/sbt-launch.jar
$ cat << EOF > sbt
SBT_OPTS="-Xms512M -Xmx1536M -Xss1M -XX:+CMSClassUnloadingEnabled -XX:MaxPermSize=256M"
java \$SBT_OPTS -jar \`dirname \$0\`/sbt-launch.jar "\$@"
EOF
$ chmod 0755 sbt

Create a project/build.properties file which supplies the version of SBT:-

$ mkdir -p project
$ cat << EOF > project/build.properties
sbt.version=0.13.7
EOF

Add an SBT plugin file to include the Play Framework plugins:-

$ cat << EOF > project/plugins.sbt
// The Typesafe repository
resolvers += "Typesafe repository" at "https://repo.typesafe.com/typesafe/releases/"
 
// Use the Play sbt plugin for Play projects
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.3.8")
EOF

// Use the Play sbt plugin for Play projects
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.3.8")
EOF

Define a buildfile for your project (note that the spaces between lines are mandatory)

$ cat << EOF > build.sbt
name := "LearnPlay"
 
version := "1.0.0-SNAPSHOT"
 
lazy val root = (project in file(".")).enablePlugins(PlayScala)
EOF

version := "1.0.0-SNAPSHOT"

lazy val root = (project in file(".")).enablePlugins(PlayScala)
EOF

That’s all the basic Play build time infrastructure set up. Now we move on to creating your application-specific parts.

Create a conf/application.conf file to hold your default crypto key (for session signing and default Crypto calls):-

$ mkdir -p conf
$ cat << EOF > conf/application.conf
application.secret="this_will_be_replaced_shortly"
EOF

Make Play generate a new application secret

$ ./sbt play-update-secret

Next we need a conf/routes file which maps the URLs to the application controllers

$ cat << EOF > conf/routes
GET / controllers.Application.index
EOF

This says “for any GET / request, use the controllers.Application.index function”. So we need that too.

$ mkdir -p app/controllers
$ cat << EOF > app/controllers/Application.scala
package controllers
 
import play.api.mvc._
 
object Application extends Controller {
     def index = TODO
}
EOF

import play.api.mvc._

object Application extends Controller {
def index = TODO
}
EOF

Now you can fire up your first basic Scala Play app

$ ./sbt ~run

and point your web browser to http://localhost:9000 to see the result – a purple TODO page. (Note that I used a tilde before the run command above – this puts it in reloadable mode, so that any changes to the source files are recompiled without having to restart SBT).

Not hugely exciting, so let’s change it.

Modify the app/controllers/Application.scala and replace

def index = TODO

with

def index = Action { Ok("Success") }

and refresh your browser to see a simple Success message.

Hardly HTML, right? So now we can explore the Templates function of Play.

First, we need a HTML template

$ mkdir -p app/views
$ cat << EOF > app/views/index.scala.html
@(message: String)
 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
</head>
<body>
<p>Hello @message</p>
</body>
</html>
EOF

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
</head>
<body>
<p>Hello @message</p>
</body>
</html>
EOF

This creates a Play View which takes a single string parameter called “message”. We use this later to say hello in the body. Now modify the app/controllers/Application.scala file to use this view.

def index = Action { Ok(views.html.index("world!")) }

See that we’re passing “world!” to the template. Reload your browser to see Hello World in all it’s glory.

Code available via Git under tag 1.0, and deployed to Heroku.

2 Comments on “Scala Play from scratch”

Jeffrey Wokocha says:

March 24, 2015 at 11:21 am

Well presented starting point. I am following these and hope you will have time to keep adding new posts.
- Andrew Gorton says:
  
  March 24, 2015 at 12:29 pm
  
  You’re very welcome. Hope everything is good with you!

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2 Comments on “Scala Play from scratch”