Make the objects serializable with kotlinx.serialization

Transcript

1. Make the objects serializable
   with kotlinx.serialization
   Keishin Yokomaku (@KeithYokoma)

   potatotips #67
   

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2. Make the objects serializable with kotlinx.serialization
   About Me
   ▸ Keishin Yokomaku
   ▸ @KeithYokoma: GitHub / Twitter / Qiita / Stack Overflow
   ▸ Merpay, Inc. / Engineer
   ▸ Fun: Gymnastics / Cycling / Photography / Motorsport / Camping
   potatotips #67
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3. Make the objects serializable with kotlinx.serialization
   kotlinx.serialization
   ▸ https://github.com/Kotlin/kotlinx.serialization
   ▸ Cross-platform / Multi-platform reflectionless serialization for Kotlin
   ▸ Supports JSON/CBOR/Protobuf formats
   ▸ Works on Kotlin/JVM, Kotlin/JS and Kotlin/Native
   potatotips #67
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4. Make the objects serializable with kotlinx.serialization
   kotlinx.serialization 101
   ▸ 1. Add kotlinx.serialization plugin
   ▸ 2. Add kotlinx.serialization runtime into dependency
   ▸ 3. Annotate with @Serializable
   ▸ 4. Serialize an object with formatter
   potatotips #67
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5. Make the objects serializable with kotlinx.serialization
   1. Add kotlinx.serialization plugin
   buildscript {

   

   ext.kotlin_version = '1.3.61'

   

   repositories {

   jcenter()

   }

   

   dependencies {

   classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

   }

   }
   5
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6. Make the objects serializable with kotlinx.serialization
   1. Add kotlinx.serialization plugin / project_root/build.gradle
   buildscript {

   

   ext.kotlin_version = '1.3.61'

   

   repositories {

   jcenter()

   }

   

   dependencies {

   classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

   classpath "org.jetbrains.kotlin:kotlin-serialization:$kotlin_version"

   }

   }
   6
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7. Make the objects serializable with kotlinx.serialization
   1. Add kotlinx.serialization plugin / module_root/build.gradle
   apply plugin: "kotlin"
   dependencies {
   implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
   }
   7
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8. Make the objects serializable with kotlinx.serialization
   1. Add kotlinx.serialization plugin / module_root/build.gradle
   apply plugin: "kotlin"
   apply plugin: "kotlinx.serialization"
   dependencies {
   implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
   }
   8
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9. Make the objects serializable with kotlinx.serialization
   2. Add kotlinx.serialization runtime into dependency
   apply plugin: "kotlin"
   apply plugin: "kotlinx.serialization"
   dependencies {
   implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
   implementation "org.jetbrains.kotlinx:kotlinx-serialization-runtime:
   0.14.0" // not $kotlin_version!!!
   }
   9
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10. Make the objects serializable with kotlinx.serialization
    3. Annotate with @Serializable
    data class SampleScreenState(
    val familyName: String,
    val givenName: String,
    val age: Int
    )
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11. Make the objects serializable with kotlinx.serialization
    3. Annotate with @Serializable
    @Serializable
    data class SampleScreenState(
    val familyName: String,
    val givenName: String,
    val age: Int
    )
    11
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12. Make the objects serializable with kotlinx.serialization
    4. Serialize an object with formatter
    @Serializable
    data class SampleScreenState(
    val familyName: String,
    val givenName: String,
    val age: Int
    )
    val originalState = SampleScreenState("foo", "bar", 30)
    12
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13. Make the objects serializable with kotlinx.serialization
    4. Serialize an object with formatter
    @Serializable
    data class SampleScreenState(
    val familyName: String,
    val givenName: String,
    val age: Int
    )
    val originalState = SampleScreenState("foo", "bar", 30)
    val json = Json(JsonConfiguration.Stable)
    13
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14. Make the objects serializable with kotlinx.serialization
    4. Serialize an object with formatter
    @Serializable
    data class SampleScreenState(
    val familyName: String,
    val givenName: String,
    val age: Int
    )
    val originalState = SampleScreenState("foo", "bar", 30)
    val json = Json(JsonConfiguration.Stable)
    // {"familyName":"foo","givenName":"bar","age":30}
    val serialized = json.stringify(originalState)
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15. Make the objects serializable with kotlinx.serialization
    4. Serialize an object with formatter
    @Serializable
    data class SampleScreenState(
    val familyName: String,
    val givenName: String,
    val age: Int
    )
    val originalState = SampleScreenState("foo", "bar", 30)
    val json = Json(JsonConfiguration.Stable)
    // {"familyName":"foo","givenName":"bar","age":30}
    val serialized = json.stringify(originalState)
    val restoredState =

    json.parse(SampleScreenState::class.serializer(), serialized)
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16. Make the objects serializable with kotlinx.serialization
    4. Serialize an object with formatter
    @Serializable
    data class SampleScreenState(
    val familyName: String,
    val givenName: String,
    val age: Int
    )
    val originalState = SampleScreenState("foo", "bar", 30)
    val json = Json(JsonConfiguration.Stable)
    // {"familyName":"foo","givenName":"bar","age":30}
    val serialized = json.stringify(originalState)
    val restoredState =

    json.parse(SampleScreenState::class.serializer(), serialized)
    println(originalState == restoredState) // true
    16
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17. Make the objects serializable with kotlinx.serialization
    kotlinx.serialization extended
    ▸ Polymorphic serialization for sealed classes
    ▸ Make non-serializable objects in a library serializable
    17
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18. Make the objects serializable with kotlinx.serialization
    Polymorphic serialization for sealed classes
    18
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    sealed class SampleType
    data class FooType(val text: String = "foo") : SampleType()
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(val d: SampleType)
    

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19. Make the objects serializable with kotlinx.serialization
    Polymorphic serialization for sealed classes
    19
    potatotips #67
    @Serializable
    sealed class SampleType
    @Serializable
    data class FooType(val text: String = "foo") : SampleType()
    @Serializable
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(val d: SampleType)
    

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20. Make the objects serializable with kotlinx.serialization
    Polymorphic serialization for sealed classes
    20
    potatotips #67
    @Serializable
    sealed class SampleType
    @Serializable
    data class FooType(val text: String = "foo") : SampleType()
    @Serializable
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(val d: SampleType)
    val originalState = SampleScreenState(FooType())
    val json = Json(JsonConfiguration.Stable)
    // {"d":{"type":"com.sample.FooType", "text":"foo"}}
    val serialized = json.stringify(originalState)
    

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21. Make the objects serializable with kotlinx.serialization
    Polymorphic serialization for sealed classes: prior to 0.14.0
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    sealed class SampleType
    data class FooType(val text: String = "foo") : SampleType()
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(val d: SampleType)
    val json = Json(JsonConfiguration.Stable)
    // Don’t know how to serialize FooType
    val serialized = json.stringify(SampleScreenState(FooType()))
    

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22. Make the objects serializable with kotlinx.serialization
    Polymorphic serialization for sealed classes: prior to 0.14.0
    22
    potatotips #67
    sealed class SampleType
    @Serializable
    data class FooType(val text: String = "foo") : SampleType()
    @Serializable
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(@Polymorphic val d: SampleType)
    val json = Json(JsonConfiguration.Stable)
    // Still don’t know how to serialize FooType
    val serialized = json.stringify(SampleScreenState(FooType()))
    

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23. Make the objects serializable with kotlinx.serialization
    Polymorphic serialization for sealed classes: prior to 0.14.0
    23
    potatotips #67
    sealed class SampleType
    @Serializable
    data class FooType(val text: String = "foo") : SampleType()
    @Serializable
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(@Polymorphic val d: SampleType)
    val sampleTypeModule = SerializersModule {
    polymorphic {
    addSubclass()
    addSubclass()
    }
    }
    val json = Json(JsonConfiguration.Stable, sampleTypeModule)
    // {"d":{"type":"com.sample.FooType", "text":"foo"}}
    val serialized = json.stringify(SampleScreenState(FooType()))
    

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24. Make the objects serializable with kotlinx.serialization
    Make non-serializable objects in a library serializable
    24
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    // Assume SampleType is in the library and cannot have @Serializable
    sealed class SampleType
    data class FooType(val text: String = "foo") : SampleType()
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(val d: SampleType)
    val json = Json(JsonConfiguration.Stable)
    // Don’t know how to serialize FooType
    val serialized = json.stringify(SampleScreenState(FooType()))
    

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25. Make the objects serializable with kotlinx.serialization
    Make non-serializable objects in a library serializable
    25
    potatotips #67
    // Assume SampleType is in the library and cannot have @Serializable
    sealed class SampleType
    data class FooType(val text: String = "foo") : SampleType()
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(@Polymorphic val d: SampleType)
    val json = Json(JsonConfiguration.Stable)
    // Still don’t know how to serialize FooType
    val serialized = json.stringify(SampleScreenState(FooType()))
    

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26. Make the objects serializable with kotlinx.serialization
    Make non-serializable objects in a library serializable
    26
    potatotips #67
    // Assume SampleType is in the library and cannot have @Serializable
    sealed class SampleType
    data class FooType(val text: String = "foo") : SampleType()
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(@Polymorphic val d: SampleType)
    val sampleTypeModule = SerializersModule {
    polymorphic {
    addSubclass() // Need to have serializer for FooType
    addSubclass() // Need to have serializer for BarType
    }
    }
    val json = Json(JsonConfiguration.Stable, sampleTypeModule)
    // Still don’t know how to serialize FooType
    val serialized = json.stringify(SampleScreenState(FooType()))
    

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27. Make the objects serializable with kotlinx.serialization
    Make non-serializable objects in a library serializable
    27
    potatotips #67
    // Assume SampleType is in the library and cannot have @Serializable
    sealed class SampleType
    data class FooType(val text: String = "foo") : SampleType()
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(@Polymorphic val d: SampleType)
    object FooTypeSerializer : KSerializer { /* implementation */ } // define how to serialize FooType
    object BarTypeSerializer : KSerializer { /* implementation */ } // define how to serialize BarType
    val sampleTypeModule = SerializersModule {
    polymorphic {
    addSubclass(FooTypeSerializer)
    addSubclass(BarTypeSerializer)
    }
    }
    val json = Json(JsonConfiguration.Stable, sampleTypeModule)
    // {"d":{"type":"com.sample.FooType", "text":"foo"}}
    val serialized = json.stringify(SampleScreenState(FooType()))
    

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28. Make the objects serializable with kotlinx.serialization
    Make non-serializable objects in a library serializable
    28
    potatotips #67
    // Assume SampleType is in the library and cannot have @Serializable
    sealed class SampleType
    data class FooType(val text: String = "foo") : SampleType()
    object FooTypeSerializer : KSerializer {
    /* implementation */
    }
    

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29. Make the objects serializable with kotlinx.serialization
    Make non-serializable objects in a library serializable
    29
    potatotips #67
    // Assume SampleType is in the library and cannot have @Serializable
    sealed class SampleType
    data class FooType(val text: String = "foo") : SampleType()
    object FooTypeSerializer : KSerializer {
    override val descriptor =

    object : SerialClassDescImpl(FooType::class.java.name) {
    init {
    // remember this element is the first element (index = 0)
    addElement("text")
    }
    }
    }
    

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30. Make the objects serializable with kotlinx.serialization
    Make non-serializable objects in a library serializable
    30
    potatotips #67
    // Assume SampleType is in the library and cannot have @Serializable
    sealed class SampleType
    data class FooType(val text: String = "foo") : SampleType()
    object FooTypeSerializer : KSerializer {
    override val descriptor = // ……
    override fun deserialize(decoder: Decoder): FooType {
    val input = decoder.beginStructure(descriptor)
    val text = input.decodeStringElement(descriptor, 0)
    input.endStructure(descriptor)
    return FooType(text)
    }
    }
    

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31. Make the objects serializable with kotlinx.serialization
    Make non-serializable objects in a library serializable
    31
    potatotips #67
    // Assume SampleType is in the library and cannot have @Serializable
    sealed class SampleType
    data class FooType(val text: String = "foo") : SampleType()
    object FooTypeSerializer : KSerializer {
    override val descriptor = // ……
    override fun serialize(encoder: Encoder, obj: FooType) {
    val output = encoder.beginStructure(descriptor)
    val text = output.encodeStringElement(descriptor, 0, obj.text)
    output.endStructure(descriptor)
    }
    }
    

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32. Make the objects serializable with kotlinx.serialization
    Drawback
    32
    potatotips #67
    @Serializable
    sealed class SampleType
    @Serializable
    data class FooType(val type: String = "foo") : SampleType()
    @Serializable
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(val d: SampleType)
    val originalState = SampleScreenState(FooType())
    val json = Json(JsonConfiguration.Stable)
    // {"d":{"type":"com.sample.FooType", "type":"foo"}}
    val serialized = json.stringify(originalState)
    // cannot restore because the JSON parser will take the latter "type" value
    val restored = json.parse(SampleScreenState::class.serializer(), serialized)
    

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33. Make the objects serializable with kotlinx.serialization
    Workaround #1: change the key for FQCN
    33
    potatotips #67
    @Serializable
    sealed class SampleType
    @Serializable
    data class FooType(val type: String = "foo") : SampleType()
    @Serializable
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(val d: SampleType)
    val originalState = SampleScreenState(FooType())
    val json = Json(JsonConfiguration.Stable.copy(classDiscriminator = "kclass"))
    // {"d":{"kclass":"com.sample.FooType", "type":"foo"}}
    val serialized = json.stringify(originalState)
    val restored = json.parse(SampleScreenState::class.serializer(), serialized)
    

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34. Make the objects serializable with kotlinx.serialization
    Workaround #2: Use array polymorphism
    34
    potatotips #67
    @Serializable
    sealed class SampleType
    @Serializable
    data class FooType(val type: String = "foo") : SampleType()
    @Serializable
    data class BarType(val flag: Boolean = false) : SampleType()
    @Serializable
    data class SampleScreenState(val d: SampleType)
    val originalState = SampleScreenState(FooType())
    val json = Json(JsonConfiguration.Stable.copy(useArrayPolymorphism = true))
    // {"d":["com.sample.FooType", {"type":"foo"}]}
    val serialized = json.stringify(originalState)
    val restored = json.parse(SampleScreenState::class.serializer(), serialized)
    

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35. Make the objects serializable with kotlinx.serialization
    Wrap up: kotlinx.serialization
    ▸ Cross-platform / Multi-platform reflectionless serialization for Kotlin
    ▸ Supports JSON/CBOR/Protobuf formats
    ▸ Works on Kotlin/JVM, Kotlin/JS and Kotlin/Native
    ▸ Compiler help us making the object serializable :)
    potatotips #67
    35
    

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36. Make the objects serializable
    with kotlinx.serialization
    Keishin Yokomaku (@KeithYokoma)

    potatotips #67
    

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