Say "hi" to Moshi (Android Budapest meetup - January 2020)

JSON serialization is an everyday task for Android developers, but it's still not a trivial one. Long used solutions such as Gson have serious pain points, especially when using them with Kotlin. Could Moshi be our saviour when it comes to dealing with JSON on Android? We'll look at how to use it, what problems it solves, and how nicely it plays with our favourite JVM language.

Talk recording: https://www.youtube.com/watch?v=qadYVYc-8mc

1. Say “hi” to zsmb.co zsmb13 Márton Braun Moshi
3. Serialization @zsmb13
4. JSON Serialization @zsmb13
5. @zsmb13
6. @zsmb13
7. Gson github.com/google/gson @zsmb13
8. Gson 101 val burger: Burger = Gson().fromJson("{...}", Burger::class.java) val json: String = Gson().toJson(Burger()) @zsmb13
9. Gson 101 val burger: Burger = Gson().fromJson("{...}", Burger::class.java) val json: String = Gson().toJson(Burger()) @zsmb13
10. Gson 101 val burger: Burger = Gson().fromJson("{...}", Burger::class.java) val json: String = Gson().toJson(Burger()) @zsmb13
11. Gson 101 val gson = Gson() val burger: Burger = Gson().fromJson("{...}", Burger::class.java) val json: String = Gson().toJson(Burger()) @zsmb13
12. Gson 101 val gson = Gson() val burger: Burger = gson.fromJson("{...}", Burger::class.java) val json: String = gson.toJson(Burger()) @zsmb13
13. Gson val gson = Gson() val burger: Burger = gson.fromJson("{...}", Burger::class.java) val json: String = gson.toJson(Burger()) 101 @zsmb13
14. Gson val gson = Gson() : built-in types @zsmb13
15. Gson val gson = Gson() gson.toJson(Date()) : built-in types @zsmb13
16. Gson val gson = Gson() gson.toJson(Date()) "Jan 30, 2020 7:03:50 PM" : built-in types @zsmb13
17. Gson val gson = Gson() gson.toJson(Date()) "Jan 30, 2020 7:03:50 PM" gson.toJson(Calendar.getInstance()) : built-in types @zsmb13
18. Gson val gson = Gson() gson.toJson(Date()) "Jan 30, 2020 7:03:50 PM" gson.toJson(Calendar.getInstance()) {"year":2020,"month":0,"dayOfMonth":30,"hourOfDay":19, "minute":03,"second":50} : built-in types @zsmb13
19. Gson val gson = Gson() gson.toJson(Date()) "Jan 30, 2020 7:03:50 PM" gson.toJson(Calendar.getInstance()) {"year":2020,"month":0,"dayOfMonth":30,"hourOfDay":19, "minute":03,"second":50} gson.toJson(Random()) : built-in types @zsmb13
20. Gson val gson = Gson() gson.toJson(Date()) "Jan 30, 2020 7:03:50 PM" gson.toJson(Calendar.getInstance()) {"year":2020,"month":0,"dayOfMonth":30,"hourOfDay":19, "minute":03,"second":50} gson.toJson(Random()) {"seed":{"value":137564286790437},"nextNextGaussian":0.0, "haveNextNextGaussian":false} : built-in types @zsmb13
21. Gson: field naming val gson = Gson() @zsmb13
22. Gson: field naming val gson = GsonBuilder() .create() @zsmb13
23. val gson = GsonBuilder() .setFieldNamingPolicy( FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES) .create() Gson: field naming @zsmb13
24. val gson = GsonBuilder() .setFieldNamingPolicy( FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES) .create() Gson: field naming data class Burger( val name: String, val totalCost: Int, val salesPrice: Int ) @zsmb13
25. val gson = GsonBuilder() .setFieldNamingPolicy( FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES) .create() Gson: field naming data class Burger( val name: String, val totalCost: Int, val salesPrice: Int ) gson.toJson(Burger("Classic", 10, 13)) {"name":"Classic","total_cost":10,"sales_price":13} @zsmb13
26. @SerializedName("name") @SerializedName("total_cost") @SerializedName("sales_price") Gson() Gson: field naming gson.toJson(Burger("Classic", 10, 13)) {"name":"Classic","total_cost":10,"sales_price":13} data class Burger( val gson = val name: String, val totalCost: Int, ) val salesPrice: Int @zsmb13
27. Gson: missing data Gson() val gson = @zsmb13
28. data class Burger( val name: String, val price: Int ) Gson: missing data Gson() val gson = @zsmb13
29. data class Burger( val name: String, val price: Int ) Gson: missing data val burger = gson.fromJson("{\"name\": \"Cheeseburger\"}", Burger::class.java) Gson() val gson = @zsmb13
30. data class Burger( val name: String, val price: Int ) Gson: missing data val burger = gson.fromJson("{\"name\": \"Cheeseburger\"}", Burger::class.java) Burger(name=Cheeseburger, price=0) Gson() val gson = @zsmb13
31. data class Burger( val name: String, val description: String ) val gson = Gson() Gson: missing data val burger = gson.fromJson("{\"name\": \"Cheeseburger\"}", Burger::class.java) @zsmb13
32. data class Burger( val name: String, val description: String ) val gson = Gson() Gson: missing data val burger = gson.fromJson("{\"name\": \"Cheeseburger\"}", Burger::class.java) Burger(name=Cheeseburger, description=null) @zsmb13
33. data class Burger( val name: String, val description: String = "One of our best burgers!" ) val gson = Gson() Gson: missing data val burger = gson.fromJson("{\"name\": \"Cheeseburger\"}", Burger::class.java) @zsmb13
34. data class Burger( val name: String, val description: String = "One of our best burgers!" ) val gson = Gson() Gson: missing data val burger = gson.fromJson("{\"name\": \"Cheeseburger\"}", Burger::class.java) Burger(name=Cheeseburger, description=null) @zsmb13
35. val gson = Gson() Gson: malformed data @zsmb13
36. val gson = Gson() Gson: malformed data data class Burger(val name: String, val price: Int) data class Restaurant(val menu: List<Burger>) @zsmb13
37. val gson = Gson() Gson: malformed data data class Burger(val name: String, val price: Int) data class Restaurant(val menu: List<Burger>) val json = """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" @zsmb13
38. val gson = Gson() Gson: malformed data data class Burger(val name: String, val price: Int) data class Restaurant(val menu: List<Burger>) val json = """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" @zsmb13
39. val gson = Gson() Gson: malformed data data class Burger(val name: String, val price: Int) data class Restaurant(val menu: List<Burger>) val json = """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" val restaurant = gson.fromJson(json, Restaurant::class.java) @zsmb13
40. Gson: malformed data val gson = Gson() data class Burger(val name: String, val price: Int) data class Restaurant(val menu: List<Burger>) val json = """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" val restaurant = gson.fromJson(json, Restaurant::class.java) Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.NumberFormatException: For input string: "crocodile" @zsmb13
41. val gson = Gson() Gson: malformed data data class Burger(val name: String, val price: Int) data class Restaurant(val menu: List<Burger>) val json = """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "" } ] }""" val restaurant = gson.fromJson(json, Restaurant::class.java) Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.NumberFormatException: For input string: "" @zsmb13
42. Say “hi” to zsmb.co zsmb13 Márton Braun Moshi
43. Moshi github.com/square/moshi @zsmb13
44. Okio github.com/square/okio Retrofit github.com/square/retrofit Moshi github.com/square/moshi OkHttp github.com/square/okhttp @zsmb13
45. Moshi github.com/square/moshi @zsmb13
46. Moshi 101 def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" @zsmb13
47. public JavaBurger(String name, int price) { this.name = name; this.price = price; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getPrice() { return price; } public void setPrice(int price) { this.price = price; } Moshi 101 } public class JavaBurger { private String name; private int price; @zsmb13
48. // ... public JavaBurger(String name, int price) { this.name = name; this.price = price; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getPrice() { return price; } public void setPrice(int price) { this.price = price; } Moshi 101 } public class JavaBurger { private String name; private int price; @zsmb13
49. // ... public JavaBurger(String name, int price) { this.name = name; this.price = price; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getPrice() { return price; } public void setPrice(int price) { this.price = price; } Moshi 101 val moshi = Moshi.Builder().build() } public class JavaBurger { private String name; private int price; @zsmb13
50. // ... public JavaBurger(String name, int price) { this.name = name; this.price = price; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getPrice() { return price; } public void setPrice(int price) { this.price = price; } Moshi 101 val moshi = Moshi.Builder().build() val json = moshi.toJson(JavaBurger("Classic", 10)) } public class JavaBurger { private String name; private int price; @zsmb13
51. // ... Moshi 101 val moshi = Moshi.Builder().build() val json = moshi.toJson(JavaBurger("Classic", 10)) } public class JavaBurger { private String name; private int price; @zsmb13
52. // ... Moshi 101 val moshi = Moshi.Builder().build() val json = moshi.toJson(JavaBurger("Classic", 10)) } public class JavaBurger { private String name; private int price; val burgerAdapter: JsonAdapter<JavaBurger> = moshi.adapter(JavaBurger::class.java) @zsmb13
53. // ... Moshi 101 val moshi = Moshi.Builder().build() } public class JavaBurger { private String name; private int price; val burgerAdapter: JsonAdapter<JavaBurger> = moshi.adapter(JavaBurger::class.java) val json = burgerAdapter.toJson(JavaBurger("Classic", 10)) @zsmb13
54. // ... Moshi 101 val moshi = Moshi.Builder().build() } public class JavaBurger { private String name; private int price; val burgerAdapter: JsonAdapter<JavaBurger> = moshi.adapter(JavaBurger::class.java) val json = burgerAdapter.toJson(JavaBurger("Classic", 10)) {"name":"Classic","price":10} @zsmb13
55. // ... Moshi 101 val moshi = Moshi.Builder().build() } public class JavaBurger { private String name; private int price; val burgerAdapter: JsonAdapter<JavaBurger> = moshi.adapter(JavaBurger::class.java) val json = burgerAdapter.toJson(JavaBurger("Classic", 10)) {"name":"Classic","price":10} val burger = burgerAdapter.fromJson(json) @zsmb13
56. Burger::class.java) val moshi = Moshi.Builder().build() (val : String, val : Int) val burgerAdapter: JsonAdapter<Burger> = moshi.adapter( Burger class name price @zsmb13 Moshi ft. Kotlin
57. Burger::class.java) val moshi = Moshi.Builder().build() (val : String, val : Int) val burgerAdapter: JsonAdapter<Burger> = moshi.adapter( Burger class name price @zsmb13 Moshi ft. Kotlin Exception in thread "main" java.lang.IllegalArgumentException: Cannot serialize Kotlin type com.example.Burger. Reflective serialization of Kotlin classes without using kotlin-reflect has undefined and unexpected behavior. Please use KotlinJsonAdapter from the moshi-kotlin artifact or use code gen from the moshi-kotlin- codegen artifact.
58. Moshi ft. Kotlin val moshi = Moshi.Builder().build() val burgerAdapter: JsonAdapter<Burger> = moshi.adapter(Burger::class.java) class Burger(val name: String, val price: Int) @zsmb13 Exception in thread "main" java.lang.IllegalArgumentException: Cannot serialize Kotlin type com.example.Burger. Reflective serialization of Kotlin classes without using kotlin-reflect has undefined and unexpected behavior. Please use KotlinJsonAdapter from the moshi-kotlin artifact or use code gen from the moshi-kotlin- codegen artifact.
59. Moshi ft. Kotlin val moshi = Moshi.Builder().build() val burgerAdapter: JsonAdapter<Burger> = moshi.adapter(Burger::class.java) class Burger(val name: String, val price: Int) @zsmb13 Exception in thread "main" java.lang.IllegalArgumentException: Cannot serialize Kotlin type com.example.Burger. Reflective serialization of Kotlin classes without using kotlin-reflect has undefined and unexpected behavior. Please use KotlinJsonAdapter from the moshi-kotlin artifact or use code gen from the moshi-kotlin- codegen artifact.
60. val moshi = Moshi.Builder().build() val burgerAdapter: JsonAdapter<Burger> = moshi.adapter(Burger::class.java) class Burger(val name: String, val price: Int) @zsmb13 Moshi ft. Kotlin Exception in thread "main" java.lang.IllegalArgumentException: Cannot serialize Kotlin type com.example.Burger. Reflective serialization of Kotlin classes without using kotlin-reflect has undefined and unexpected behavior. Please use KotlinJsonAdapter from the moshi-kotlin artifact or use code gen from the moshi-kotlin- codegen artifact.
61. val moshi = Moshi.Builder().build() val burgerAdapter: JsonAdapter<Burger> = moshi.adapter(Burger::class.java) class Burger(val name: String, val price: Int) def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" @zsmb13 Moshi: reflection
62. val moshi = Moshi.Builder().build() Moshi: reflection val burgerAdapter: JsonAdapter<Burger> = moshi.adapter(Burger::class.java) class Burger(val name: String, val price: Int) def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" implementation "com.squareup.moshi:moshi-kotlin:$moshi_version" @zsmb13
63. val moshi = Moshi.Builder() Moshi: reflection val burgerAdapter: JsonAdapter<Burger> = moshi.adapter(Burger::class.java) class Burger(val name: String, val price: Int) .build() @zsmb13
64. Moshi: reflection .add(KotlinJsonAdapterFactory()) val burgerAdapter: JsonAdapter<Burger> = moshi.adapter(Burger::class.java) class Burger(val name: String, val price: Int) .build() val moshi = Moshi.Builder() @zsmb13
65. Moshi: reflection .add(KotlinJsonAdapterFactory()) val burgerAdapter: JsonAdapter<Burger> = moshi.adapter(Burger::class.java) class Burger(val name: String, val price: Int) val json = burgerAdapter.toJson(Burger("Classic", 10)) val burger = burgerAdapter.fromJson(json) .build() val moshi = Moshi.Builder() @zsmb13
66. Moshi: reflection def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" implementation "com.squareup.moshi:moshi-kotlin:$moshi_version" @zsmb13
67. Moshi: reflection def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" implementation "com.squareup.moshi:moshi-kotlin:$moshi_version" @zsmb13 Exception in thread "main" java.lang.IllegalArgumentException: Cannot serialize Kotlin type com.example.Burger. Reflective serialization of Kotlin classes without using kotlin-reflect has undefined and unexpected behavior. Please use KotlinJsonAdapter from the moshi-kotlin artifact or use code gen from the moshi-kotlin- codegen artifact.
68. implementation moshi-kotlin:$moshi_version" "com.squareup.moshi: def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" @zsmb13 Moshi: reflection Exception in thread "main" java.lang.IllegalArgumentException: Cannot serialize Kotlin type com.example.Burger. Reflective serialization of Kotlin classes without using kotlin-reflect has undefined and unexpected behavior. Please use KotlinJsonAdapter from the moshi-kotlin artifact or use code gen from the artifact. moshi-kotlin- codegen
69. def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" kapt moshi-kotlin-codegen:$moshi_version" "com.squareup.moshi: @zsmb13 Moshi: codegen
70. dependencies { } Moshi: codegen apply plugin: 'kotlin' apply plugin: 'kotlin-kapt' def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" kapt "com.squareup.moshi:moshi-kotlin-codegen:$moshi_version" @zsmb13
71. Moshi: codegen class Burger(val name: String, val price: Int) @zsmb13
72. @JsonClass(generateAdapter = true) class Burger(val name: String, val price: Int) @zsmb13 Moshi: codegen
73. @JsonClass(generateAdapter = true) class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) val json = burgerAdapter.toJson(Burger("Double", 18))) @zsmb13 Moshi: codegen
74. dependencies { def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" implementation "com.squareup.moshi:moshi-kotlin:$moshi_version" kapt "com.squareup.moshi:moshi-kotlin-codegen:$moshi_version" } apply plugin: 'kotlin' apply plugin: 'kotlin-kapt' val moshi = Moshi.Builder() .add(KotlinJsonAdapterFactory()) .build() @zsmb13 Moshi: mixed use
75. Moshi: mixed use dependencies { def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" implementation "com.squareup.moshi:moshi-kotlin:$moshi_version" kapt "com.squareup.moshi:moshi-kotlin-codegen:$moshi_version" } apply plugin: 'kotlin' apply plugin: 'kotlin-kapt' val moshi = Moshi.Builder() .add(KotlinJsonAdapterFactory()) .build() @zsmb13
76. dependencies { def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" implementation "com.squareup.moshi:moshi-kotlin:$moshi_version" kapt "com.squareup.moshi:moshi-kotlin-codegen:$moshi_version" } apply plugin: 'kotlin' apply plugin: 'kotlin-kapt' val moshi = Moshi.Builder() .add(KotlinJsonAdapterFactory()) .build() @zsmb13 Moshi: mixed use
77. class CustomBurgerAdapter { TODO("Implement deserialization") @ToJson fun toJson(writer: JsonWriter, value: Burger?) { TODO("Implement serialization") } } @FromJson fun fromJson(reader: JsonReader): Burger? { } @zsmb13 Moshi: custom adapters
78. @FromJson fun fromJson(reader: JsonReader): Burger? { } @zsmb13 Moshi: custom adapters
79. Moshi: custom adapters @FromJson fun fromJson(reader: JsonReader): Burger? { var name: String? = null var price: Int? = null } @zsmb13
80. Moshi: custom adapters @FromJson fun fromJson(reader: JsonReader): Burger? { var name: String? = null var price: Int? = null reader.beginObject() reader.endObject() } @zsmb13
81. Moshi: custom adapters @FromJson fun fromJson(reader: JsonReader): Burger? { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { } reader.endObject() } @zsmb13
82. Moshi: custom adapters @FromJson fun fromJson(reader: JsonReader): Burger? { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.nextName()) { "name" -> name = reader.nextString() "price" -> price = reader.nextInt() else -> reader.skipValue() } } reader.endObject() } @zsmb13
83. @FromJson fun fromJson(reader: JsonReader): Burger? { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.nextName()) { "name" -> name = reader.nextString() "price" -> price = reader.nextInt() else -> reader.skipValue() } } reader.endObject() return Burger(name!!, price!!) } @zsmb13 : custom adapters Moshi
84. class BurgerJsonAdapter( moshi: Moshi ) : JsonAdapter<Burger>() { override fun toString(): String = buildString(28) { append("GeneratedJsonAdapter(").append("Burger").append(')') } private val options: JsonReader.Options = JsonReader.Options.of("name", "price") private val stringAdapter: JsonAdapter<String> = moshi.adapter(String::class.java, emptySet(), "name") private val intAdapter: JsonAdapter<Int> = moshi.adapter(Int::class.java, emptySet(), "price") override fun fromJson(reader: JsonReader): Burger { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.selectName(options)) { 0 -> name = stringAdapter.fromJson(reader) ?: throw Util.unexpectedNull("name", "name", reader) 1 -> price = intAdapter.fromJson(reader) ?: throw Util.unexpectedNull("price", "price", reader) -1 -> { reader.skipName() reader.skipValue() } } } reader.endObject() return Burger( name = name ?: throw Util.missingProperty("name", "name", reader), price = price ?: throw Util.missingProperty("price", "price", reader) ) } override fun toJson(writer: JsonWriter, value: Burger?) { if (value == null) { throw NullPointerException( "value was null! Wrap in .nullSafe() to write nullable values.") } writer.beginObject() writer.name("name") stringAdapter.toJson(writer, value.name) writer.name("price") intAdapter.toJson(writer, value.price) writer.endObject() } } @zsmb13 Moshi’s generated adapter
85. class BurgerJsonAdapter( moshi: Moshi ) : JsonAdapter<Burger>() { override fun toString(): String = buildString(28) { append("GeneratedJsonAdapter(").append("Burger").append(')') } private val options: JsonReader.Options = JsonReader.Options.of("name", "price") private val stringAdapter: JsonAdapter<String> = moshi.adapter(String::class.java, emptySet(), "name") private val intAdapter: JsonAdapter<Int> = moshi.adapter(Int::class.java, emptySet(), "price") Moshi’s generated adapter @zsmb13
86. private val intAdapter: JsonAdapter<Int> = moshi.adapter(Int::class.java, emptySet(), "price") override fun fromJson(reader: JsonReader): Burger { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.selectName(options)) { 0 -> name = stringAdapter.fromJson(reader) ?: throw Util.unexpectedNull("name", "name", reader) 1 -> price = intAdapter.fromJson(reader) ?: throw Util.unexpectedNull("price", "price", reader) -1 -> { reader.skipName() reader.skipValue() } } } reader.endObject() Moshi’s generated adapter @zsmb13
87. private val intAdapter: JsonAdapter<Int> = moshi.adapter(Int::class.java, emptySet(), "price") override fun fromJson(reader: JsonReader): Burger { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.selectName(options)) { 0 -> name = stringAdapter.fromJson(reader) ?: throw Util.unexpectedNull("name", "name", reader) 1 -> price = intAdapter.fromJson(reader) ?: throw Util.unexpectedNull("price", "price", reader) -1 -> { reader.skipName() reader.skipValue() } } } reader.endObject() Moshi’s generated adapter @zsmb13
88. private val intAdapter: JsonAdapter<Int> = moshi.adapter(Int::class.java, emptySet(), "price") override fun fromJson(reader: JsonReader): Burger { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.selectName(options)) { 0 -> name = stringAdapter.fromJson(reader) ?: throw Util.unexpectedNull("name", "name", reader) 1 -> price = intAdapter.fromJson(reader) ?: throw Util.unexpectedNull("price", "price", reader) -1 -> { reader.skipName() reader.skipValue() } } } reader.endObject() Moshi’s generated adapter @zsmb13
89. private val intAdapter: JsonAdapter<Int> = moshi.adapter(Int::class.java, emptySet(), "price") override fun fromJson(reader: JsonReader): Burger { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.selectName(options)) { 0 -> name = stringAdapter.fromJson(reader) ?: throw Util.unexpectedNull("name", "name", reader) 1 -> price = intAdapter.fromJson(reader) ?: throw Util.unexpectedNull("price", "price", reader) -1 -> { reader.skipName() reader.skipValue() } } } reader.endObject() Moshi’s generated adapter @zsmb13
90. private val intAdapter: JsonAdapter<Int> = moshi.adapter(Int::class.java, emptySet(), "price") override fun fromJson(reader: JsonReader): Burger { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.selectName(options)) { 0 -> name = stringAdapter.fromJson(reader) ?: throw Util.unexpectedNull("name", "name", reader) 1 -> price = intAdapter.fromJson(reader) ?: throw Util.unexpectedNull("price", "price", reader) -1 -> { reader.skipName() reader.skipValue() } } } reader.endObject() Moshi’s generated adapter @zsmb13
91. override fun toString(): String = buildString(28) { append("GeneratedJsonAdapter(").append("Burger").append(')') } private val options: JsonReader.Options = JsonReader.Options.of("name", "price") private val stringAdapter: JsonAdapter<String> = moshi.adapter(String::class.java, emptySet(), "name") private val intAdapter: JsonAdapter<Int> = moshi.adapter(Int::class.java, emptySet(), "price") override fun fromJson(reader: JsonReader): Burger { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.selectName(options)) { 0 -> name = stringAdapter.fromJson(reader) ?: throw Util.unexpectedNull("name", "name", reader) Moshi’s generated adapter @zsmb13
92. private val intAdapter: JsonAdapter<Int> = moshi.adapter(Int::class.java, emptySet(), "price") override fun fromJson(reader: JsonReader): Burger { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.selectName(options)) { 0 -> name = stringAdapter.fromJson(reader) ?: throw Util.unexpectedNull("name", "name", reader) 1 -> price = intAdapter.fromJson(reader) ?: throw Util.unexpectedNull("price", "price", reader) -1 -> { reader.skipName() reader.skipValue() } } } reader.endObject() Moshi’s generated adapter @zsmb13
93. private val options: JsonReader.Options = JsonReader.Options.of("name", "price") private val stringAdapter: JsonAdapter<String> = moshi.adapter(String::class.java, emptySet(), "name") private val intAdapter: JsonAdapter<Int> = moshi.adapter(Int::class.java, emptySet(), "price") override fun fromJson(reader: JsonReader): Burger { var name: String? = null var price: Int? = null reader.beginObject() while (reader.hasNext()) { when (reader.selectName(options)) { 0 -> name = stringAdapter.fromJson(reader) ?: throw Util.unexpectedNull("name", "name", reader) 1 -> price = intAdapter.fromJson(reader) ?: throw Util.unexpectedNull("price", "price", reader) -1 -> { Moshi’s generated adapter @zsmb13
94. throw Util.unexpectedNull("price", "price", reader) -1 -> { reader.skipName() reader.skipValue() } } } reader.endObject() return Burger( name = name ?: throw Util.missingProperty("name", "name", reader), price = price ?: throw Util.missingProperty("price", "price", reader) ) } } Moshi’s generated adapter @zsmb13
95. throw Util.unexpectedNull("price", "price", reader) -1 -> { reader.skipName() reader.skipValue() } } } reader.endObject() return Burger( name = name ?: throw Util.missingProperty("name", "name", reader), price = price ?: throw Util.missingProperty("price", "price", reader) ) } } @zsmb13 Moshi’s generated adapter
96. val moshi = Moshi.Builder().build() val adapter: JsonAdapter<Date> = moshi.adapter(Date::class.java) @zsmb13 Moshi: built-in types
97. Moshi: built-in types val moshi = Moshi.Builder().build() val adapter: JsonAdapter<Date> = moshi.adapter(Date::class.java) Exception in thread "main" java.lang.IllegalArgumentException: Platform class java.util.Date requires explicit JsonAdapter to be registered @zsmb13
98. Moshi: built-in types def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" kapt "com.squareup.moshi:moshi-kotlin-codegen:$moshi_version" val moshi = Moshi.Builder().build() val adapter: JsonAdapter<Date> = moshi.adapter(Date::class.java) @zsmb13
99. Moshi: built-in types def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" kapt "com.squareup.moshi:moshi-kotlin-codegen:$moshi_version" implementation "com.squareup.moshi:moshi-adapters:$moshi_version" val moshi = Moshi.Builder().build() val adapter: JsonAdapter<Date> = moshi.adapter(Date::class.java) @zsmb13
100. val adapter: JsonAdapter<Date> = moshi.adapter(Date::class.java) def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" implementation "com.squareup.moshi:moshi-adapters:$moshi_version" kapt "com.squareup.moshi:moshi-kotlin-codegen:$moshi_version" .add(Date::class.java, Rfc3339DateJsonAdapter()) .build() val moshi = Moshi.Builder() @zsmb13 Moshi: built-in types
101. val adapter: JsonAdapter<Date> = moshi.adapter(Date::class.java) def moshi_version = '1.9.2' implementation "com.squareup.moshi:moshi:$moshi_version" implementation "com.squareup.moshi:moshi-adapters:$moshi_version" kapt "com.squareup.moshi:moshi-kotlin-codegen:$moshi_version" .add(Date::class.java, Rfc3339DateJsonAdapter()) 2020-01-30T19:03:50.250Z .build() val moshi = Moshi.Builder() @zsmb13 Moshi: built-in types
102. @zsmb13 Moshi: field naming
103. @JsonClass(generateAdapter = true) data class Burger( @Json(name = "name") val name: String, @Json(name = "total_cost") val totalCost: Int, @Json(name = "sales_price") val salesPrice: Int ) @zsmb13 Moshi: field naming
104. @JsonClass(generateAdapter = true) data class Burger( @Json(name = "name") val name: String, @Json(name = "total_cost") val totalCost: Int, @Json(name = "sales_price") val salesPrice: Int ) moshi.adapter(Burger::class.java) .toJson(Burger("Classic", 10, 13)) @zsmb13 Moshi: field naming
105. @JsonClass(generateAdapter = true) data class Burger( @Json(name = "name") val name: String, @Json(name = "total_cost") val totalCost: Int, @Json(name = "sales_price") val salesPrice: Int ) moshi.adapter(Burger::class.java) .toJson(Burger("Classic", 10, 13)) {"name":"Classic","total_cost":10,"sales_price":13} @zsmb13 Moshi: field naming
106. @JsonClass(generateAdapter = true) data class Burger( val name: String, val total_cost: Int, val sales_price: Int ) moshi.adapter(Burger::class.java) .toJson(Burger("Classic", 10, 13)) {"name":"Classic","total_cost":10,"sales_price":13} @zsmb13 Moshi: field naming
107. @JsonClass(generateAdapter = true) data class Burger( val name: String, val price: Int ) @zsmb13 Moshi: missing data
108. @JsonClass(generateAdapter = true) data class Burger( val name: String, val price: Int ) Moshi: missing data val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\"}" ) @zsmb13
109. @JsonClass(generateAdapter = true) data class Burger( val name: String, val price: Int ) Moshi: missing data val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\"}" ) Exception in thread "main" com.squareup.moshi.JsonDataException: Required value 'price' missing at $ @zsmb13
110. @JsonClass(generateAdapter = true) data class Burger( val name: String, val description: String ) Moshi: missing data val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\"}" ) @zsmb13
111. @JsonClass(generateAdapter = true) data class Burger( val name: String, val description: String ) Moshi: missing data val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\"}" ) Exception in thread "main" com.squareup.moshi.JsonDataException: Required value 'description' missing at $ @zsmb13
112. @JsonClass(generateAdapter = true) data class Burger( val name: String, val description: String? ) Moshi: missing data val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\"}" ) @zsmb13
113. @JsonClass(generateAdapter = true) data class Burger( val name: String, val description: String? ) Moshi: missing data val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\"}" ) Burger(name=Cheeseburger, description=null) @zsmb13
114. Burger(name=Cheeseburger, description=null) @JsonClass(generateAdapter = true) data class Burger( val name: String, val description: String = "One of our best burgers!" ) Moshi: missing data val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\"}" ) @zsmb13
115. Burger(name=Cheeseburger, description=null) @JsonClass(generateAdapter = true) data class Burger( val name: String, val description: String = "One of our best burgers!" ) Moshi: missing data val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\"}" ) Burger(name=Cheeseburger, description=One of our best burgers!) @zsmb13
116. Shameless plug https://zsmb.co/primaries-matter-a-discussion-of-constructors/ @zsmb13
117. val moshi = Moshi.Builder() Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) .build() val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\", \"price\": 13}" ) @zsmb13
118. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) .add(...) val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\", \"price\": 13}" ) .build() val moshi = Moshi.Builder() @zsmb13
119. val moshi = Moshi.Builder() Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) .build() val burgerAdapter = moshi.adapter(Burger::class.java) val burger = burgerAdapter.fromJson( "{\"name\": \"Cheeseburger\", \"price\": 13}" ) @zsmb13
120. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) JsonAdapter<Burger> @zsmb13
121. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) @zsmb13
122. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int?) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) burgerAdapter.toJson(Burger("Cancelled", null)) @zsmb13
123. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int?) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) burgerAdapter.toJson(Burger("Cancelled", null)) {"name":"Cancelled"} @zsmb13
124. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int?) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) .serializeNulls() burgerAdapter.toJson(Burger("Cancelled", null)) {"name":"Cancelled","price":null} @zsmb13
125. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) burgerAdapter.toJson(null) @zsmb13
126. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) burgerAdapter.toJson(null) null @zsmb13
127. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) .nullSafe() burgerAdapter.toJson(null) null @zsmb13
128. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) .nonNull() burgerAdapter.toJson(null) @zsmb13
129. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) .nonNull() burgerAdapter.toJson(null) Exception in thread "main" com.squareup.moshi.JsonDataException: Unexpected null at $ @zsmb13
130. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) @zsmb13
131. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) burgerAdapter.fromJson( "{\"name\":\"Cheeseburger\",\"price\": 13}" ) @zsmb13
132. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) burgerAdapter.fromJson( "{\"name\":\"Cheeseburger\",\"price\": 13}" ) Burger(name=Cheeseburger, price=13) @zsmb13
133. Moshi: customization options @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) burgerAdapter.fromJson( "{\"name\":\"Cheeseburger\",\"price\": 13,\"rating\":4.2}" ) Burger(name=Cheeseburger, price=13) @zsmb13
134. @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) .failOnUnknown() burgerAdapter.fromJson( "{\"name\":\"Cheeseburger\",\"price\": 13,\"rating\":4.2}" ) Moshi: customization options @zsmb13
135. @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) val moshi = Moshi.Builder().build() val burgerAdapter = moshi.adapter(Burger::class.java) .failOnUnknown() burgerAdapter.fromJson( "{\"name\":\"Cheeseburger\",\"price\": 13,\"rating\":4.2}" ) Moshi: customization options Exception in thread "main" com.squareup.moshi.JsonDataException: Cannot skip unexpected NAME at $.rating @zsmb13
136. Moshi: malformed data @zsmb13
137. @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) @JsonClass(generateAdapter = true) data class Restaurant(val menu: List<Burger>) @zsmb13 Moshi: malformed data
138. @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) @JsonClass(generateAdapter = true) data class Restaurant(val menu: List<Burger>) val json = """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" @zsmb13 Moshi: malformed data
139. @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) @JsonClass(generateAdapter = true) data class Restaurant(val menu: List<Burger>) val json = """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" val restaurant = adapter.fromJson(json, Restaurant::class.java) @zsmb13 Moshi: malformed data
140. Moshi: malformed data @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) @JsonClass(generateAdapter = true) data class Restaurant(val menu: List<Burger>) val json = """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" val restaurant = adapter.fromJson(json, Restaurant::class.java) Exception in thread "main" com.squareup.moshi.JsonDataException: Expected an int but was crocodile at path $.menu[2].price @zsmb13
141. val json = val restaurant = adapter.fromJson(json, Restaurant::class.java) """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" Moshi: malformed data @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) @JsonClass(generateAdapter = true) data class Restaurant(val menu: List<Burger>) Exception in thread "main" com.squareup.moshi.JsonDataException: Expected an int but was crocodile at path $.menu[2].price @zsmb13
142. """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" Exception in thread "main" com.squareup.moshi.JsonDataException: Expected an int but was crocodile at path $.menu[2].price @zsmb13
143. Exception in thread "main" com.squareup.moshi.JsonDataException: Expected an int but was crocodile at path $.menu[2].price """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" @zsmb13
144. Exception in thread "main" com.squareup.moshi.JsonDataException: Expected an int but was crocodile at path $.menu[2].price """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" @zsmb13
145. Exception in thread "main" com.squareup.moshi.JsonDataException: Expected an int but was crocodile at path $.menu[2].price """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" @zsmb13
146. Moshi: malformed data @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) @JsonClass(generateAdapter = true) data class Restaurant(val menu: List<Burger>) val json = val restaurant = adapter.fromJson(json, Restaurant::class.java) """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" Exception in thread "main" com.squareup.moshi.JsonDataException: Expected an int but was crocodile at path $.menu[2].price @zsmb13
147. Moshi: malformed data @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) @JsonClass(generateAdapter = true) data class Restaurant(val menu: List<Burger>) val json = val restaurant = adapter.fromJson(json, Restaurant::class.java) """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "crocodile" } ] }""" Exception in thread "main" com.squareup.moshi.JsonDataException: Expected an int but was crocodile at path $.menu[2].price Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.NumberFormatException: For input string: "crocodile" @zsmb13
148. Moshi: malformed data @JsonClass(generateAdapter = true) data class Burger(val name: String, val price: Int) @JsonClass(generateAdapter = true) data class Restaurant(val menu: List<Burger>) val json = val restaurant = adapter.fromJson(json, Restaurant::class.java) """{ "menu": [ { "name": "Classic", "price": 10 }, { "name": "Cheeseburger", "price": 13 }, { "name": "Double", "price": "" } ] }""" @zsmb13 Exception in thread "main" com.squareup.moshi.JsonDataException: Expected an int but was at path $.menu[2].price Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.NumberFormatException: For input string: ""
149. Retrofit.Builder() .baseUrl("...") .addConverterFactory(MoshiConverterFactory.create()) .build() def retrofit_version = '2.7.1' implementation "com.squareup.retrofit2:retrofit:$retrofit_version" implementation "com.squareup.retrofit2:converter-moshi:$retrofit_version" @zsmb13 Moshi: Retrofit integration
150. Retrofit.Builder() .baseUrl("...") .addConverterFactory(MoshiConverterFactory.create()) .build() def retrofit_version = '2.7.1' implementation "com.squareup.retrofit2:retrofit:$retrofit_version" implementation "com.squareup.retrofit2:converter-moshi:$retrofit_version" val moshi = Moshi.Builder() .add(KotlinJsonAdapterFactory()) .add(...) .build() @zsmb13 Moshi: Retrofit integration
151. Retrofit.Builder() .baseUrl("...") .addConverterFactory(MoshiConverterFactory.create( .build() def retrofit_version = '2.7.1' implementation "com.squareup.retrofit2:retrofit:$retrofit_version" implementation "com.squareup.retrofit2:converter-moshi:$retrofit_version" val moshi = Moshi.Builder() .add(KotlinJsonAdapterFactory()) .add(...) .build() @zsmb13 Moshi: Retrofit integration )) moshi
152. More Moshi… •Other built-in adapters •Intermediate objects while parsing •Annotated types •Parsing arrays and other generic types •A lot more under-the-hood details! @zsmb13
153. Resources •A Few Ok Libraries (Jake Wharton, Square) – Droidcon Montreal 2015 • https://www.youtube.com/watch?v=WvyScM_S88c •Upgrading to Moshi (Eric Cochran, Pinterest) - droidcon NYC 2017 • https://www.youtube.com/watch?v=xHFs7cccnXU •JSON Explained (Jesse Wilson, Square) – Chicago Roboto 2019 • https://www.youtube.com/watch?v=1PwdqkKDCSo @zsmb13
154. Resources •Moshi, another JSON Processor (Jesse Wilson) • https://developer.squareup.com/blog/moshi-another-json-processor/ •Exploring Moshi’s codegen (Zac Sweers) • https://www.zacsweers.dev/exploring-moshis-kotlin-code-gen/ •Reflection Machines (Jesse Wilson) • https://publicobject.com/2016/03/24/reflection-machines/ •Advanced JSON parsing techniques using Moshi and Kotlin (Christophe Beyls) • https://medium.com/@BladeCoder/advanced-json-parsing-techniques- using-moshi-and-kotlin-daf56a7b963d @zsmb13
155. zsmb.co/talks zsmb13 Márton Braun › Reflection or codegen › Kotlin friendly › Really fast › Great failure modes Say “hi” to Moshi