Play in practice

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PLAY IN PRACTICE/Will Sargent @will_sargent

PREAMBLE
This is going to be a broad talk.

USAGE
This talk does not attempt to be universal to all situations.
YMMV.

WHAT IS PLAY?
Play is a web application framework.

THESIS STATEMENT
Play is awesome.

WHY PLAY IS AWESOME?
Because Play is Simple.

HERE'S WHAT PLAY DOES:
Takes in an HTTP request.
Returns (or streams) a response.

HERE'S WHAT PLAY DOESN'T DO:
It doesn't tie an HTTP request to a thread.
It doesn't tie an HTTP session to memory.
It does...

HERE'S WHAT PLAY PROVIDES AS OPTIONS:
"Always-on" Build System
HTTP API
Templates
Form Handling
JSON support

BUILD SYSTEM
Modified SBT, recompiles pages on the fly in development
mode.
Type "play idea" or "play eclipse" to generate...

FRONT CONTROLLER
Routing API (with LangPathBindable and
QueryStringBindable)
Action: asynchronous and stateless by default...

PRESENTATION
Compiled template language (Twirl, Scaml, Jade).
Built-in helpers for rendering forms.
Support for Twitter Bo...

JSON
Formatting to JSON
Parsing of JSON objects
JsPath, automatic validation, read and write combinators

SO, WHY DOES THIS MATTER?

THE BUSINESS REQUEST
Make a website!

MAKE TWO WEBSITES!
Product
Admin

MAKE MORE WEBSITES!
Product
Admin
Customer Service
Business Analytics
Business Content
Jobs Queue

THE PROBLEM
In a complex web application, many different front ends need
to look at the same data, from different angles.
...

THE SOLUTION
In complex applications, use loosely coupled, stateless,
composable services.

HOW?
Create a Play HTTP front end, backed by Akka.
Create a business domain services, backed by Akka.
Use Akka to pass mes...

ALAN KAY ON OOP
“ I thought of objects being like biological cells
and/or individual computers on a network,
only able to ...

COMMAND / QUERY RESPONSIBILITY
SEGREGATION (CQRS)
Command: a message intending a change of state.
Event: a message indicat...

CQRS MAPPED ONTO PLAY
Processing Commands using POST
Querying for Data with GET
Broadcasting Events with Streaming

PROCESSING COMMANDS
Validate all input.
where possible.
Be very careful when handling passwords and credit card
numbers.
U...

COMMANDS
def sendCommand(command : Command) : Future[Either[Fault,Event]]

CQRS

COMMAND
trait Command extends Product
sealed abstract class AuthenticationCommand extends Command
case class AuthenticateW...

EVENT
case class UserAuthenticatedEvent(userId: UserID,
series: Option[Long] = None,
token: Option[Long] = None)
extends A...

FAULT
trait AuthenticationFault
case class InvalidSessionCookieFault() extends AuthenticationFault

QUERY
case class UserInfo(id: UUID, email: Email, fullName: String)
class UserInfoService {
def lookup(uuid: UUID)(implici...

QUERY PRACTICES:
Objects should be immutable
Return ranges or streams over unbounded lists.
Don't expose repository logic ...

CONTEXT AND AUTHENTICATION
Use or to set up a
WrappedRequest context.
Pass the request context around implicitly in every
...

EXAMPLE TEMPLATE
@(u: UserInfo)(implicit ctx: Context)
@layout(title = "User Page") {
@ctx.me.map { u =>
<p>
This is your ...

STREAMING
You send an event.
Event goes through an Iteratee.
Iteratee broadcasts event using Socket and Hub model.
Play us...

EVERYTHING ELSE
Logging
Metrics
Testing

LOGGING
Play's internal logger isn't the greatest.
Fortunately, it's not hardcoded and you can ignore it.
Make your own wr...

METRICS
has a Scala option.
Map it through Global's onRequest method.
Metrics

TESTING
Unit testing a stateless app is very easy.
Swapping out services with mocks/stubs may be easier
with DI (I use Sub...

LOAD TESTING
Use jconsole and .
Don't know how useful Typesafe Console is.
Apache JMeter

QUESTIONS?
There's an award!

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