Kotlin is the new upcoming JVM language and is well known for Android development. However, the popularity of Kotlin in server-side applications has been growing exponentially over the last years. Embracing simplicity, readability, and interoperability, Kotlin profiles itself as the new way to go. Most of the Java applications are written in Java 8 nowadays and people are looking around to upgrade to Java 11 or even migrating to Kotlin. Both are promoted as the new way to go and both have their own strengths. During a live coding session, steps of a smooth migration to Kotlin are demonstrated.

1. Upgrade Time! Choose Java 11
or the other one… Kotlin!
Paulien van Alst
Amsterdam | April 2-3, 2019

2. Who am I?
@PaulienVanAlst

3. Highlights Java 9/10/11
switch statements
var something = “Something”
JShell
Convenience methods for collections
Release cadence

4. My story with Kotlin
boardGameRepository.findAllByCategory(ADVENTURE).stream()
.filter(game -> game.getMinimalNumberOfPlayers() > 2)
.filter(game -> game.getMinimalAge() > 10)
.map(BoardGameEntity::getPrice)
.reduce(BigDecimal.ZERO, BigDecimal::add);

5. My story with Kotlin
boardGameRepository.findAllByCategory(ADVENTURE).stream()
.filter(game -> game.getMinimalNumberOfPlayers() > 2)
.filter(game -> game.getMinimalAge() > 10)
.map(BoardGameEntity::getPrice)
.reduce(BigDecimal.ZERO, BigDecimal::add);
boardGameRepository.findAllByCategory(ADVENTURE)
.moreThanTwoPlayers()
.olderThanTenToPlay()
.meanPrice()

6. My story with Kotlin
boardGameRepository.findAllByCategory(ADVENTURE).stream()
.filter(game -> game.getMinimalNumberOfPlayers() > 2)
.filter(game -> game.getMinimalAge() > 10)
.map(BoardGameEntity::getPrice)
.reduce(BigDecimal.ZERO, BigDecimal::add);
boardGameRepository.findAllByCategory(ADVENTURE)
.moreThanTwoPlayers()
.olderThanTenToPlay()
.meanPrice()

7. My story with Kotlin
boardGameRepository.findAllByCategory(ADVENTURE).stream()
.filter(game -> game.getMinimalNumberOfPlayers() > 2)
.filter(game -> game.getMinimalAge() > 10)
.map(BoardGameEntity::getPrice)
.reduce(BigDecimal.ZERO, BigDecimal::add);
boardGameRepository.findAllByCategory(ADVENTURE)
.moreThanTwoPlayers()
.olderThanTenToPlay()
.meanPrice()

8. My story with Kotlin
boardGameRepository.findAllByCategory(ADVENTURE).stream()
.filter(game -> game.getMinimalNumberOfPlayers() > 2)
.filter(game -> game.getMinimalAge() > 10)
.map(BoardGameEntity::getPrice)
.reduce(BigDecimal.ZERO, BigDecimal::add);
boardGameRepository.findAllByCategory(ADVENTURE)
.moreThanTwoPlayers()
.olderThanTenToPlay()
.meanPrice()

9. My story with Kotlin
boardGameRepository.findAllByCategory(ADVENTURE).stream()
.filter(game -> game.getMinimalNumberOfPlayers() > 2)
.filter(game -> game.getMinimalAge() > 10)
.map(BoardGameEntity::getPrice)
.reduce(BigDecimal.ZERO, BigDecimal::add);
boardGameRepository.findAllByCategory(ADVENTURE)
.moreThanTwoPlayers()
.olderThanTenToPlay()
.meanPrice()

10. Reasons to switch to Kotlin
Regular updates
Interoperability
Multiplatform
Readability
Less boilerplate
Safe programming

11. What to keep in mind
Interoperability
Idioms
Magic problem solver

12. Warning!
DO this at home
or
In a POC

13. Let’s start!
Rates 6 8
Games above … 8 9 9,5

14. Let’s start!
Spring boot 2
In memory database
UT’s and IT’s

15. Migration Plan
1. Set-up dependencies
2. Migrate PoJo’s
3. Rewrite unit tests
4. Core logic
5. Configuration
6. Test DSL

16. Let’s start
Code!

17. Migration Plan
1. Set-up dependencies
2. Migrate PoJo’s
3. Rewrite unit tests
4. Core logic
5. Configuration
6. Test DSL

19. Thank you!
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