A short introduction (with many examples) to the Scala programming language and also an introduction to using the Play! Framework for modern, safe, efffcient and reactive web applications.

1. Short intro to Scala and the
Play! Framework
50 - 60 minutes
Last updated: Sept 2014 falmeida1988@gmail.com
Leveraging modern programming techniques to make
safer, faster and more predictable applications

2. Scala - First encounter
def hello() = {
println("Hello, world!")
}
var aMap = Map("Red" -> "Apple", "Yellow" -> "Peach")
aMap += ("Purple" -> "Grape")
def factorial(x: BigInt): BigInt =
if (x == 0) 1 else x * factorial(x - 1)
class MyClass(index: Int, name: String)
functions
collections
recursive functions
classes

3. Scala - Background
● Created by Martin Odersky at EPFL in 2003
● Aimed at overcoming Java’s weaknesses while allowing for easy migration
for former Java developers
● One of the few object-functional languages (also: F#)
● One of the JVM-compliant languages (also: groovy, clojure, jruby, jython)

4. Scala selling points
● Functional/Object Oriented hybrid - use one, the other, or both
● More elegant, less painful concurrency constructs
● Uncluttered, concise syntax
● Seamless interoperability and compatibility with Java
● Typing: expressive type system / static typing / type safety / type inference

5. Quick syntax walkthrough
● no type declaration prior to use (due to type-inference)
var msg = "Hello, world!"
● braces are only needed for multiline blocks
def max(x: Int, y: Int) = if (x > y) x else y
def max2(x: Int, y: Int) = {
if (x > y) x
else y
}
no braces
yes braces

6. Quick syntax walkthrough
● no semicolons at the end (unless you want multiple statements)
println(line); println(line)
println(line)
println(line)
equivalent code

7. Quick syntax walkthrough
● type comes after variable name (only when required or for usability)
def max(x: Int, y: Int): Int =
if (x > y) x else y
val m = new HashMap[Int, String] ()
required types for
val m1: Map[Int, String] = new HashMap()
arguments
optional return type
either is acceptable
not necessary to annotate both sides
val m2: HashMap[Int, String] = new HashMap[Int, String] ()

8. Quick syntax walkthrough
● val for immutable variables, var for mutable variables
val msg = "Hello, world!"
msg = "Another message!" // ERROR: reassignment to val
var msg2 = "Hello, world!"
msg2 = "Another message!" // no error

9. Quick syntax walkthrough
● statements also return a value (if, for, while, def) - which means they are
also expressions
var result1 = ""
if(marks >= 50)
result = "passed"
else
result = "failed"
val result2 = if(marks >= 50)
"passed"
else
"failed"
using if as a
statement
if as an expression

10. Quick syntax walkthrough
● return statements are allowed but generally not needed
def multiply(a: Int,b:Int):Int =
return a*b
def sum(x:Int,y:Int) =
x + y
def greet() = println( "Hello, world!" )
explicitly using return
When no return is provided,
last value computed by the
function is returned
Functions that return no
useful values have a result
type of Unit

11. Quick syntax walkthrough
● function literals or anonymous functions
(x: Int) => x * 2
val double = (x: Int) => x * 2
● example usage: as parameter to function map:
List(1,2,3,4,5).map{ (x: Int) => x * 2 }
//evaluates to List(2, 4, 6, 8, 10)
a function that takes an Int
and multiplies it by two
function value being
assigned to a variable
function map takes another
function as argument

12. Scala, Java Comparison
scala class MyClass(index: Int, name: String)
class MyClass {
private int index;
private String name;
public MyClass(int index, String name) {
this.index = index;
this.name = name;
}
}
java

13. Scala, Java Comparison
scala val nameHasUpperCase = name.exists(_.isUpper)
boolean nameHasUpperCase = false;
for (int i = 0; i < name.length(); ++i) {
if (Character.isUpperCase(name.charAt(i))) {
nameHasUpperCase = true;
break;
}
}
java

14. Scala, Java Interoperability
● You can use Java code in Scala as-is (i.e. no changes needed).
● Scala classes can subclass Java classes, you can instantiate Java classes
in Scala, you can access methods, fields (even if they are static), etc.
● You can also use Scala code in Java projects, as long as you don’t use
many advanced Scala concepts that are not possible in Java.
● Similar code generated by Scala and Java usually generates the exact
same bytecode, as can be verified using tools like javap

15. Environment
● Console
● sbt - dependency and package management
● JVM integration
● Typesafe products (Akka, Play, Activator, Spray, Slick, etc)
● All of your favourite Java libraries
● Testing suites (Unit, Integration, Acceptance, Property-based, etc)
● Small but high-level community

16. Weaknesses
● It’s a large language. Users are advised not to try to use many different
concepts at the same time, especially when starting out.
● Scala has a somewhat steep learning curve and its complex type system is
powerful but hard to grasp at times.
● Implicit conversions are useful but easily misused and may make code
harder to understand.
● Complex function signatures may put some off.

17. Play Framework
● MVC Web Framework; supports Java and Scala
● Created in 2007
● Used at Linkedin, Coursera, The Guardian, etc.
● Uses sbt for dependency management
● As of September 2014, it has had 5000 commits by over 350 contributors.
● The Simplest Possible Play App

18. Play Features
● Play has all default features one can expect from a modern framework:
○ MVC-based separation of concerns
○ Support for ORMs (Java) or FRMs (Scala)
○ Rich models with support for Forms, Validation, etc.
○ Database Migration (called evolutions)
○ Template engine (Scala-based)
○ Extensive routing
○ Support for REST-only Apps
○ Lots of community-provided plugins
○ Supported by Typesafe

19. Play - Application Layout
app/ -- Application sources
| assets/ -- LESS, Coffeescript sources
| controllers/ -- Controllers
| models/ -- Domain models
| views/ -- Templates
build.sbt -- Build configuration
conf/ -- Configuration files
| application.conf -- Main configuration file
| routes -- Routes definition
public/ -- Public folder (CSS, JS, etc)
project/ -- sbt configuration files
logs/ -- Logs
target/ -- Generated files - ignore
test/ -- Sources for tests

20. Play Framework - Examples
● Displaying a view from a controller action
package controllers
import play.api._
import play.api.mvc._
object Application extends Controller {
def index = Action {
Ok(views.html.index("Your new application is ready."))
}
}
import libraries
create a controller
define actions as methods

21. Play Framework - Examples
● Displaying a view with some data
package controllers
import models._
import play.api._
import play.api.mvc._
import play.api.Play.current
object Application extends Controller {
this method returns a List[Computer]
def index = Action { implicit request =>
val computers = Computer .list
Ok(views.html.web.index( "Hello! I'm the WEB!" , computers))
}
}
the Computer model was defined in
package models (not shown here)
instantiate a view file and feed it
a string and a list of computers

22. Activator
● Web-based IDE and project viewer, built by Typesafe
● A large number of sample applications (templates) to study and learn from

23. Resources
● Scala Programming Language (Wikipedia Article)
● Scala official site
● Typesafe
● Programming in Scala Book on Amazon
● A preset Virtual Machine for Scala/Play Development
● Functional Programming Principles in Scala on Coursera
● Principles of Reactive Programming on Coursera
● Play Framework Official Website
● ScalaJavaInterop Project
● Play Framework (Wikipedia Article)
● Using Scala on Heroku
● Typesafe Activator
● All Available Activator Templates