Kotlin Backend Development 6 Yrs Recap. The Good, the Bad and the Ugly
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NEXT Insurance is a US based insurtech startup, revolutionizing the small business insurance industry. NEXT was founded 6 years ago and ever since we have been building our microservices in Kotlin. During this period we grew from a small startup with one backend developer(myself) to a $4B company with 150 backend developers. We have written over 1.2M lines of code in Kotlin and aquired long mileage with this programming language. In this talk I am going to share our experiences, insights and pains. This talk was given in JFokus 2022
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Kotlin Backend Development 6 Yrs Recap. The Good, the Bad and the Ugly
- 1. Kotlin Backend Development 5 Yrs Recap. The Good, the Bad and the Ugly Haim Yadid VP Technology @ Next Insurance
- 2. Kotlin Backend Development 6 Yrs Recap. The Good, the Bad and the Ugly Haim Yadid VP Technology @ Next Insurance
- 4. NEXT 4
- 7. NEXT 7
- 8. NEXT 8
- 9. NEXT 9
- 10. NEXT #Backend Developers 1 2016 2017 8 150 2022 This is important
- 12. NEXT Kotlin Version 1.0.2 2016 2017 1.1.50 1.6.10 2022
- 14. NEXT 14 ● Working flawlessly in production ● Smooth Onboarding of Java developers ● Good IDE support ● Community Adoption is growing ● Selling point for hiring
- 16. NEXT 16 Some Short stories: Kotlin Promises Are mostly kept
- 17. NEXT Main Tech Stack Components AWS EC2 K8s JVM Kotlin Dropwizard Jetty Jersey Logback JDBI Guice JUNIT Flyway RDS Kotlin Script 17 Jackson
- 18. NEXT Main Tech Stack Components AWS EC2 K8s 18
- 19. NEXT Main Tech Stack Components JUNIT 19
- 20. NEXT Main Tech Stack Components JVM Kotlin 20 AWS EC2 K8s
- 21. NEXT Main Tech Stack Components JVM Kotlin Kotlin Script 21 Policy Rating Formula Rating Formulas Other versions AWS EC2 K8s
- 22. NEXT Main Tech Stack Components Dropwizard Jetty Jersey Logback JDBI Guice 22 Jackson
- 23. NEXT Main Tech Stack Components Flyway RDS 23
- 24. NEXT Main Tech Stack Components AWS EC2 K8s JVM Kotlin Dropwizard Jetty Jersey Logback JDBI Guice JUNIT Flyway RDS Kotlin Script 24 Jackson
- 25. NEXT 25 Data classes - The Prince that was Promised data class AddressInfo( val telephone: String, val street: String, val num: Int, val city: String, val zipCode: String, val state: State? ) ● Widely used >6100 data classes ● Used for DTO, DAO ● Rest API Serialization / deserialization with jackson ● hashcode/equals/(se|ge)tters saves a lot of boilerplate ● copy() helps working with immutable objects
- 26. NEXT 26 Data Classes - Jackson Serialization fun ObjectMapper.applyNiSettings(): ObjectMapper {
- 27. NEXT 27 Data Classes - Jackson Serialization fun ObjectMapper.applyNiSettings(): ObjectMapper { return this .registerModule(KotlinModule())
- 28. NEXT 28 Data Classes - Jackson Serialization fun ObjectMapper.applyNiSettings(): ObjectMapper { return this .registerModule(KotlinModule()) .configure( DeserializationFeature .FAIL_ON_UNKNOWN_PROPERTIES, false)
- 29. NEXT 29 Data Classes - Jackson DeSerialization fun ObjectMapper.applyNiSettings(): ObjectMapper { return this .registerModule(KotlinModule()) .configure( DeserializationFeature .FAIL_ON_UNKNOWN_PROPERTIES, false) .configure( DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES, true) }
- 30. NEXT 30 The Promise of Null Safety val productVersion:String = versions[versionId] Map<String,Sting>
- 31. NEXT 31 The Promise of Null Safety val productVersion:String? = versions[versionId] Map<String,Sting>
- 32. NEXT 32 The Promise of Null Safety val productVersion:String = versions[versionId]!! NullPointerException
- 33. NEXT 33 The Promise of Null Safety val productVersion:String = versions.require(versionId) A better NullPointerException
- 34. NEXT 34 The Promise of Null Safety val productVersion:String = versions[versionId]!! require(productVersion.status == Staged) { "Version $versionId: Can't unstage status…" } versions[versionId] = productVersion.copy( status = ProductVersionStatus.Draft, updatedBy = updatedBy)
- 35. NEXT 35 The Promise of Null Safety ● Null Safety Mechanisms baked in the type system ● No more NPEs ? ● ( not really) >11052 invocations of !! ● Where do they come from ○ interacting with Java based third party libraries ○ Getting values from maps
- 36. NEXT 36 <|*|>
- 37. NEXT 37 Operator Overloading ● 155 overloads (plus,minus,times,get,invoke) ● Most usages makes sense operator fun times(factor: BigDecimal) = … operator fun plus(toAdd: AmountWithAttribution) = … operator fun minus(toSubtract: AmountWithAttribution) = operator fun compareTo(other: AmountWithAttribution) =
- 38. NEXT 38 Extension Functions fun MutableList<Int>.swap(index1: Int, index2: Int) { val tmp = this[index1] // 'this' corresponds to the list this[index1] = this[index2] this[index2] = tmp }
- 39. NEXT 39 Extension Functions private fun String.
- 40. NEXT 40 Extension Functions private fun String.isVersionLowerThan( thatVersion: String) = when { isValidSpecificBranchVersion(thatVersion) && this==thatVersion -> false //same branch isValidSpecificBranchVersion(thatVersion) -> true
- 41. NEXT 41 Extension Functions fun String.isVersionLowerThan( thatVersion: String) = when { isValidSpecificBranchVersion(thatVersion) && this==thatVersion -> false //same branch isValidSpecificBranchVersion(thatVersion) -> true
- 42. NEXT 42 Extension Functions - my preferance private fun isVersionLowerThan( thisVersion:String , thatVersion: String) = …
- 43. NEXT 43 Extension Functions data class WhateverDTO(val state: State, @field:NotBlank val zipCode: String, @field:NotBlank val city: String, @field:NotBlank val streetAddress: String )
- 44. NEXT 44 Extension Functions data class WhateverDTO(val state: State, @field:NotBlank val zipCode: String, @field:NotBlank val city: String, @field:NotBlank val streetAddress: String ) fun WhateverDTO.getAsParamValue() = "${streetAddress}$EOL${city}, ${state.dbName} $zipCode"
- 45. NEXT 45 Our concurrency model & Tx Ctx Jetty Worker Thread CTX Worker Thread CTX Worker Thread CTX Worker Thread CTX Thread Pool(s) Worker Thread CTX Worker Thread CTX Worker Thread CTX Worker Thread CTX Ctx: (MDC) TransactionID Caller Flow OpenID Span
- 46. NEXT 46 Executors - fixing context fun Executor.executeWithContext(r: Runnable) { execute(r) }
- 47. NEXT 47 Executors - MDC Usage fun Executor.executeWithContext(r: Runnable) { val mdcContextInfo = MDCContextInfo.fromMDC() val activeSpan = GlobalTracer.get().activeSpan() val rWithContext = Runnable { mdcContextInfo.populateMDC() GlobalTracer.get().activateSpan(activeSpan) r.run() } execute(rWithContext) }
- 48. NEXT 48 Coroutines : launch fun CoroutineScope.launchWithContext( ): Job = launch( ) also async ,runBlocking, flowOn
- 49. NEXT 49 Coroutines : launch fun CoroutineScope.launchWithContext( context: CoroutineContext = EmptyCoroutineContext, start: CoroutineStart = CoroutineStart.DEFAULT, block: suspend CoroutineScope.() -> Unit ): Job = launch(MDCContext() + context, start, block) also asyncWithContext,runBlockingWithContext, flowOnWithContext
- 50. NEXT 50 Type Aliases From Kotlin documentation: Type aliases provide alternative names for existing types. If the type name is too long you can introduce a different shorter name and use the new one instead. It's useful to shorten long generic types. For instance, it's often tempting to shrink collection types: typealias NodeSet = Set<Network.Node> typealias FileTable<K> = MutableMap<K, MutableList<File>>
- 51. NEXT 51 Type Aliases - The feature we use too much typealias AffiliateId = Int typealias AgencyId = Int typealias AgencyAggregatorId = Int typealias AgentId = String typealias BundleId = Int typealias BusinessId = String . . . // additional 50 type aliases Controversial in the community as well ○ https://medium.com/@amlcurran/a voiding-primitive-obsession-in-swift -5325b65d521e ○ https://medium.com/@jerzy.chalup ski/kotlin-the-missing-parts-67645d 9a02f4
- 52. NEXT 52 typealias ZipCode = String typealias Address = String fun main() { var zip: ZipCode = "56934" val addr: Address = "bb" zip = addr } Type Aliases - Are not Type Safe
- 53. NEXT 53 abstract class SomeClassResponse( open val success: Success, open val responseMessage: ResponseMessage) Type Aliases - What is behind the magic typealias Success = Boolean typealias ResponseMessage = String
- 54. NEXT 54 abstract class SomeClassResponse( open val success: Boolean, open val responseMessage: String) Type Aliases - What is behind the magic
- 55. NEXT 55 @Deprecated("Stop using me") data class DeprecateMe(val a: String, val b: String) typealias IamNotDeprecatedAndILikeIt = DeprecateMe fun main() { val a = DeprecateMe("a", "b") val c = IamNotDeprecatedAndILikeIt("a", "b") Type Aliases - Hides Deprecation
- 56. NEXT 56 private typealias ValidationResults = List<Pair<OTPValidationResponse, DigitsPasswordData>> Put Type Aliases to Good Use typealias Row = Array<String> typealias StringMatrix = List<Array<String>>
- 57. NEXT 57 @JvmInline value class NiJexlExpression( val expressionString: String) Inline Classes to the rescue ● Prefer inline classes instead of typealias ● Type safety at compilation ● Migration is not so easy. ● There is a problem with inline classes and our current Jackson Version ● Type erased at runtime ….(Heap Dumps ?)
- 58. NEXT 58 A Migration Story Java11 -> Java 17
- 59. NEXT 59 Migrations along the Years ● Migration to Kotlin 1.1.0 ( Java8 support ) was smooth ● Migration to (almost) every version of kotlin immediately ● Migration to Java 11 – only a year ago ) ● Migration to Java 17 – 5 months ago
- 60. NEXT NEXT Build Time Gradle 7.2 Compiler & Bytecode 11 Kotlin Compiler 1.4 libraries 1.5.21 Run Time Kotlin Runtime 1.5.21 JVM 11 / 16 JRE 11 / 16 60 September 2021
- 61. NEXT Proprietary & Confidential NEXT Kotlin - Java Bytecode Compatibility ● Kotlin 1.4.10 supports Java 14 Bytecode (class version) ● Kotlin 1.4.21 supports Java 15 Bytecode (class version) ● Kotlin 1.5.21 supports Java 16 Bytecode (class version) ● By the time java 17 was released 1.7 bytecode was not supported 61 Kotlin
- 62. NEXT NEXT Gradle - Java bytecode Compatibility Gradle https://docs.gradle.org/current/userguide/compatibility.html 62
- 63. NEXT Kotlin API deprecation @Deprecated("Use minOrNull instead." , ReplaceWith("this.minOrNull()")) @DeprecatedSinceKotlin (warningSince = "1.4", errorSince = "1.5", hiddenSince = "1.6") @SinceKotlin("1.1") public fun Iterable<Double>.min(): Double? { return minOrNull() } min() max() minBy() maxBy() minOrNull() maxOrNull() minByOrNull() maxByOrNull() 63
- 64. NEXT Detaching gradle compiler version 64 val kotlinVersion = libs.findVersion("kotlin").get() // 1.6.10 opposed to 1.5.31 from gradle implementation("org.jetbrains.kotlin:kotlin-gradle-plug in:$kotlinVersion") implementation("org.jetbrains.kotlin:kotlin-script-runt ime:$kotlinVersion")
- 66. THANKS.