From Java to Scala in Less Than Three Months

Alexander Kops
Started at Zalando in 2010
Delivery Lead, Brand Solutions

15 countries
3 fulfillment centers
16+ million active customers
2.2+ billion € revenue 2014
130+ million visits per month
10.000+ employees,
~900 in tech
Zalando at a Glance
Visit us: tech.zalando.com

Legacy Tech Stack
2008 - 2010

Legacy Tech Stack
Complete rebuild in 2010

Zalando Tech Employees

Radical Agility
Purpose
Autonomy
Mastery

Rules of P lay
Microservices
REST APIs
API First
SaaS principle
Cloud: Build on top of AWS

Brand Solutions
Formed in 2014
Creating a CMS for our fashion brands
Uploading their own content to the Zalando shop
Five teams, 50+ people

My Team’s Challenge
Build new analytics product
Gather + compute data from different sources
Potential future growth
Work with legacy applications
Be ready for cloud deployment

Why we chose Scala
Experience with the JVM
Works well with Java libraries
Mature ecosystem
Backed by Typesafe
Functional programming good for parallelization

Why we chose Play
Intuitive to use
Excellent performance
Extensibility
Backed by Typesafe

Scala: the Good Parts

Concise

Combines FP and OOP

Library design choices

Easy parallelization

Great DSLs for testing

Scala: the bad parts

Compilation times
Advanced language features add to compile time
scalac -Xshow-phases
But sbt’s incremental compilation helps!

Language problems
The same thing can be written in many different ways
No canonical style guide
Allows “operator overloading”
FP code can get unreadable

Introducing Scala

Steep learning curve
New language
Functional programming concepts
New frameworks
New build tool

Helping the transition
Assume 3-4 weeks overhead
Two weeks exclusively for learning
Encourage study groups
Bring in freelancers
Incremental learning OO -> FP

Provide material

Fitting projects
Prototypes
Greenfield projects
Modular projects: Layered approach

Two types of Scala converts
Using Scala as Java
Functional programming hipsters

About coding style
Develop own or embrace existing style guide
Pair programming and code reviews
Strict compiler settings

Tooling
IntelliJ > Eclipse IDE
sbt provides benefits over Maven and Gradle

Hiring Scala developers
Genuine Scala developers are rare
Senior Java developers eager to learn Scala
Provide internal trainings
Spread the word that you are doing Scala

Our application

Typesafe Stack in Zalando
40% of engineers want to learn Scala
>12 teams are developing in Play and Scala
>40 engineers
Four Typesafe-certified Scala and Play trainers in-house

Other applications
Merchant Center
Fraud analysis
Stylist website
A/B testing tool
Payment services

Play-Swagger
“API First” library for Play
Developed in-house by two engineers
Collaboration with Typesafe’s James Roper
https://github.com/zalando/play-swagger

Follow us
Tech Blog: tech.zalando.com
GitHub: github.com/zalando
Twitter: @ZalandoTech
Instagram: zalandotech