How the right architecture can simplify migrating to Kotlin

Do you want to migrate your Java codebase to Kotlin, but are you not sure where to start? And how to do that in small steps? This talk shows you how architecture patterns like hexagonal, vertical slice, and domain driven design can enable you to do just that, while at the same time increasing your code quality!

Presented at: KotlinDevDay 2021

Transcript

1. Simplify migrating to Kotlin How the right architecture can Nico Krijnen
2. Nico Krijnen @nicokrijnen nkrijnen nicokrijnen
3. Why migrate to Kotlin?
4. Why migrate to Kotlin? NullPointerException
 70% of Production Environments #1 Source: overops.com
5. Why migrate to Kotlin?
6. Why migrate to Kotlin? https://youtu.be/2yXtZ8x7TXw?t=569 Shared mutable data needs synchronisation
7. Java 2 Kotlin
8. Just press convert!
9. Just press convert!
10. Rewrite time! Rewrite time?
11. Rewrite time! Rewrite time?
12. Rewrite time! Rewrite time?
13. Rewrite time! Rewrite time?
14. Techniques Hexagonal Vertical slice Value objects Encapsulation Tests
15. Side-step Understanding Hexagonal architecture... Direction of dependency Hexagonal – Vertical Slice – Value Objects – Encapsulation – Tests
16. Direction of dependency
17. Direction of dependency
18. Controlling direction of dependency
19. Controlling direction of dependency
20. Controlling direction of dependency
21. Controlling direction of dependency
28. Techniques Hexagonal architecture Hexagonal – Vertical Slice – Value Objects – Encapsulation – Tests
29. Source: github.com/Sairyss/domain-driven-hexagon
31. Dependencies only point inward
32. ✓ More modular ✓ Clear separation ✓ Swap implementations Architectural benefits Tradeoffs: ❌ Have to add abstractions ❌ Can be hard not to leak details in those abstractions
33. Core with no dependencies ✓ Easy to test ✓ Easy to change ✓ Easy to reason about
34. How does that help migrate to Kotlin? ✓ Isolate most important code ✓ Kotlin where it matters most ✓ Outside can remain Java ✓ Outside modules can be isolated from each other
35. How does that help migrate to Kotlin? ✓ Isolate most important code ✓ Kotlin where it matters most ✓ Outside can remain Java ✓ Outside modules can be isolated from each other
36. How to start?
37. Techniques Vertical slice architecture Hexagonal – Vertical Slice – Value Objects – Encapsulation – Tests
38. Vertical slices
39. Vertical slices
40. Vertical slices
41. Architectural benefits ✓ Clear separation ✓ Isolated & modular ✓ High cohesion ✓ Low coupling ✓ Minimise feature complexity
42. Vertical slices make it easy to ✓ Keep a feature in your head ✓ Refactor code ✓ Understand usage ✓ Prevent coupling ✓ Take small steps ✓ Limit your blast radius
43. How does that help migrate to Kotlin? ✓ Introduce Kotlin feature-by-feature ✓ Evolve architecture feature-by-feature ✓ Take small steps
44. Techniques Value objects Hexagonal – Vertical Slice – Value Objects – Encapsulation – Tests
45. Value objects
46. Value objects
47. Value objects
48. Validation
49. Value objects
50. (De)Serialization
51. How does that help migrate to Kotlin? ✓ Easy to write in Kotlin ✓ Introduce them
 one at a time ✓ Take small steps
52. Techniques Encapsulation Hexagonal – Vertical Slice – Value Objects – Encapsulation – Tests
53. Encapsulation
54. Encapsulation
55. Encapsulation
56. Encapsulation
57. Encapsulation makes it easy to ✓ Keep a feature in your head ✓ Refactor code ✓ Understand usage ✓ Freely change implementation ✓ Limit your blast radius ✓ Take small steps
58. Tests And what if you have none... Hexagonal – Vertical Slice – Value Objects – Encapsulation – Tests
59. Test suite quality Do not accept: ❌ Flakey tests ❌ Slow tests ❌ Bad test isolation ❌ Missing assertions ❌ Testing implementation details
60. How does Kotlin help with tests? Test code should: ✓ Be readable ✓ Communicate intent of module Kotlin helps here through: ✓ Expressiveness ✓ DSL capabilities Write a failing test Make the test pass Refactor
61. What about the old tests?
62. What if you have no tests? “Legacy Code is code without tests” Michael Feathers: Working Effectively with Legacy Code
63. What if you have no tests? "There is only one way to eat an elephant: a bite at a time." understandlegacycode.com “Legacy Code is code without tests” Michael Feathers: Working Effectively with Legacy Code
64. Techniques Hexagonal Vertical slice Value objects Encapsulation Tests
65. Take small steps
66. How the right architecture can Simplify migrating to Kotlin Take small steps Nico Krijnen @nicokrijnen nkrijnen nicokrijnen