Upgrading to Moshi - Speaker Deck

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Upgrading to Moshi Eric Cochran Droidcon San Francisco November 5, 2017

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Moshi?

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Moshi? JSON serialization library for Java with a streaming and object-mapping API

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Moshi? JSON serialization library for Java with a streaming and object-mapping API and Kotlin

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Moshi? JSON serialization library for Java with a streaming and object-mapping API Gson 3 Lite and Kotlin

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Why update from Gson? Inactive

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Why update from Gson? Inactive Too lenient

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Why update from Gson? Inactive Too lenient Large API

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Why update from Gson? Inactive Too lenient Large API Inconsistent exceptions (Moshi has IOExceptions and JsonDataExceptions)

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Why update from Gson? Inactive Too lenient Large API Inconsistent exceptions (Moshi has IOExceptions and JsonDataExceptions) ~188KB, 1345 methods (Moshi is 112KB, 759 methods)

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Why update from Gson? Inactive Too lenient Large API Inconsistent exceptions (Moshi has IOExceptions and JsonDataExceptions) ~188KB, 1345 methods (Moshi is 112KB, 759 methods) Moshi optimizations and API niceties…

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Moshi optimizations Share buffer segments with other Okio users

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Moshi optimizations Share buffer segments with other Okio users Avoid allocating strings while deserializing JsonReader.selectName(Options)

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How to Upgrade

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FieldNamingPolicy https://publicobject.com/2016/01/20/strict-naming-conventions-are-a-liability/

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Reﬂective ﬁeld renaming @SerializedName("the_name")

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Reﬂective ﬁeld renaming @SerializedName("the_name") @Json(name = "the_name")

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Reﬂective ﬁeld renaming @SerializedName("the_name") @Json(name = "the_name") Prefer using the domain’s naming convention

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Streaming API com.google.gson.stream.JsonReader com.google.gson.stream.JsonWriter

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Streaming API com.google.gson.stream.JsonReader com.google.gson.stream.JsonWriter It’s the same! com.squareup.moshi.JsonReader com.squareup.moshi.JsonWriter

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Streaming API com.google.gson.stream.JsonReader com.google.gson.stream.JsonWriter It’s the same! com.squareup.moshi.JsonReader com.squareup.moshi.JsonWriter Bonus: JsonReader.Options

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Streaming API com.google.gson.stream.JsonReader com.google.gson.stream.JsonWriter It’s the same! com.squareup.moshi.JsonReader com.squareup.moshi.JsonWriter Bonus: JsonReader.Options Bonus: JsonReader.setFailOnUnknown

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JsonReader.Options Prepare strings ahead of time: Options.of("key1", "key2") Read out directly from the source: JsonReader.selectName(options), JsonReader.selectString(options) Returns index of string in Options

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setFailOnUnknown JsonReader.setFailOnUnknown(true) Fail when JsonReader.skipValue() is called to ensure you are not missing any JSON data while debugging

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Object Mapping TypeAdapter

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Object Mapping TypeAdapter JsonAdapter

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Object Mapping TypeAdapter JsonAdapter No document-level API like Gson.fromJson

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Object Mapping TypeAdapter JsonAdapter No document-level API like Gson.fromJson Gson.getAdapter(TypeToken)

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Object Mapping TypeAdapter JsonAdapter No document-level API like Gson.fromJson Gson.getAdapter(TypeToken) Moshi.adapter(Type)

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Object Mapping TypeAdapter JsonAdapter No document-level API like Gson.fromJson Gson.getAdapter(TypeToken) Moshi.adapter(Type) Cache your adapters! https://publicobject.com/2016/03/24/reflection-machines/

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Object Mapping without Footgun Platform types require user-registered JsonAdapters moshi.adapter(java.util.Date.class) moshi.adapter(java.util.ArrayList.class) moshi.adapter(android.graphics.Point.class)

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Object Mapping JsonAdapter wrappers serializeNulls() nullSafe() lenient() indent(String) failOnUnknown()

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Object Mapping JsonSerializer JsonDeserializer

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Object Mapping JsonSerializer JsonDeserializer These don’t stream!

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Object Mapping TypeAdapter TypeAdapterFactory

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Object Mapping TypeAdapter TypeAdapterFactory JsonAdapter JsonAdapter.Factory

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Object Mapping TypeToken

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Object Mapping TypeToken java.lang.reflect.Type com.squareup.moshi.Types factory methods

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Object Mapping TypeToken java.lang.reflect.Type com.squareup.moshi.Types factory methods TypeToken.getParameterized(List.class, String.class)

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Object Mapping TypeToken java.lang.reflect.Type com.squareup.moshi.Types factory methods TypeToken.getParameterized(List.class, String.class) Types.newParameterizedType(List.class, String.class)

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Object Mapping Unknown Enums enum Exercise { run, jump, walk } exerciseTypeAdapter.fromJson("jog") == null

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Object Mapping Unknown Enums enum Exercise { run, jump, walk } exerciseTypeAdapter.fromJson("jog") == null exerciseJsonAdapter.fromJson("jog") throws JsonDataException

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Object Mapping Unknown Enums enum Exercise { run, jump, walk } exerciseTypeAdapter.fromJson("jog") == null exerciseJsonAdapter.fromJson("jog") throws JsonDataException EnumWithDefaultValueJsonAdapter https://goo.gl/85U7Pu Moshi API for fallback enums?

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Object Mapping with JsonQualiﬁers Special-case type qualifiers class Data { @JsonAdapter(WrappedStringTypeAdapter.class) String string; }

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Object Mapping with JsonQualiﬁers Special-case type qualifiers class Data { @JsonAdapter(WrappedStringTypeAdapter.class) String string; } @Retention(RUNTIME) @JsonQualiﬁer @interface WrappedString {} class Data { @WrappedString String string; }

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Object Mapping with JsonQualiﬁers class WrappedStringTypeAdapter extends TypeAdapter { String read(JsonReader reader) throws IOException { reader.beginObject(); String string = reader.nextString(); reader.endObject(); return string; } }

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Object Mapping with JsonQualiﬁers class WrappedStringAdapter { @FromJson @WrappedString String fromJson(JsonReader reader) throws IOException { reader.beginObject(); String string = reader.nextString(); reader.endObject(); return string; } }

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Easier JsonAdapters class PointJsonAdaperFactory implements JsonAdapter.Factory { JsonAdapter> create(Type type, Set extends Annotation> annotations, Moshi moshi) { if (Types.getRawType(types) != Point.class) return null; return new JsonAdapter { Point fromJson(JsonReader reader) {...} void toJson(JsonWriter writer, Point value) {...} } } }

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Even Easier JsonAdapters @FromJson Foo fromJson(JsonReader reader) @FromJson Foo fromJson(JsonReader reader, JsonAdapter delegate, ) // Bar is a type that can already be deserialized. @FromJson Foo fromJson(Bar value)

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Even Easier JsonAdapters @ToJson void toJson(JsonWriter writer, Foo value) @ToJson void toJson(JsonWriter writer, JsonAdapter delegate, ) @ToJson void toJson(JsonWriter writer, Foo value, JsonAdapter delegate, ) // Bar is a type that can already be serialized. @FromJson Bar fromJson(Foo value)

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Polymorphic Types class Animal { String type; } List animals = animalAdapter.fromJson(source)

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Polymorphic Types class Animal { String type; } List animals = animalAdapter.fromJson(source) class Dog extends Animal { String bark; } class Cat extends Animal { int meals; }

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Polymorphic Types JsonElement (JsonObject, JsonArray, String, primitives)

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Polymorphic Types JsonElement (JsonObject, JsonArray, String, primitives) Object (Map, List, String, primitives)

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Polymorphic Types Gson class AnimalTypeAdapter extends TypeAdapter { TypeAdapter elementAdapter; TypeAdapter catAdapter; TypeAdapter dogAdapter; Animal read(JsonReader in) { JsonObject value = elementAdapter.read(in).getAsJsonObject(); // Inspect the value. Decide what TypeAdapter to delegate to. if (value.get("type").getAsString().equals("cat")) return catAdapter.fromJsonTree(value); // ... } }

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Polymorphic Types Moshi class AnimalJsonAdapter extends JsonAdapter { JsonAdapter catAdapter; JsonAdapter dogAdapter; Animal fromJson(JsonReader in) { Map value = (Map) in.readJsonValue(); // Inspect the value. Decide what JsonAdapter to delegate to. if (value.get("type").equals("cat")) return catAdapter.fromJsonValue(value); // ... } }

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Polymorphic Types RuntimeTypeAdapterFactory

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Polymorphic Types RuntimeTypeAdapterFactory ???

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Updating Piecemeal

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Retrofit AnnotatedConverterFactory https://goo.gl/nhLt8z @Moshi for new code Retrofit retrofit = new Retrofit.Builder().baseUrl(server.url("/")) .addConverterFactory(new AnnotatedConverterFactory.Builder() .add(com.example.Moshi.class, moshiConverterFactory) .add(com.example.Gson.class, gsonConverterFactory) .build()) .addConverterFactory(gsonConverterFactory) // Fallback. .build(); interface Service { @GET("/new_endpoint") @com.example.Moshi Call newEndpoint(); @GET("/old_endpoint") @Gson Call oldEndpoint(); @GET("/old_endpoint") Call oldEndpointDefault(); // Will use fallback. }

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Auto-Value-Moshi https://github.com/rharter/auto-value-moshi @AutoValue abstract class Data { abstract String string(); static JsonAdapter jsonAdapter(Moshi moshi) { return new AutoValue_Data.MoshiJsonAdapter(moshi); } }

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Auto-Value-Moshi https://github.com/rharter/auto-value-moshi @MoshiAdapterFactory abstract class MyJsonAdapterFactory implements JsonAdapter.Factory { static JsonAdapter.Factory create() { return new AutoValueMoshi_MyJsonAdapterFactory(); } }

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Kotlin

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KotlinJsonAdapter data class TrainStation(val name: String, val cost: Int = 250) { "name": "Reading" }

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KotlinJsonAdapter data class TrainStation(val name: String, val cost: Int = 250) { "name": null } { }

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KotlinJsonAdapter data class TrainStation(val name: String = "Reading", val cost: Int = 250) { "name": null } { }

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KotlinJsonAdapter data class TrainStation(val name: String, val cost: Int = 250, val trains: List) { "name": "Reading", "cost": "1000", "trains": [ {…}, null ] } val train = station.trains[1]

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KotlinJsonAdapter val moshi = Moshi.Builder() // Add any other JsonAdapter factories. .add(KotlinJsonAdapterFactory()) .build()

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KotlinJsonAdapter val moshi = Moshi.Builder() // Add any other JsonAdapter factories. .add(KotlinJsonAdapterFactory()) .build() fun withKotlinJsonAdapterFactory(moshi: Moshi) = moshi.newBuilder().add(KotlinJsonAdapterFactory()).build()

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Resources medium.com/square-corner-blog/moshi-another-json-processor-624f8741f703 “A Few Ok Libraries” https://youtu.be/WvyScM_S88c stackoverflow.com/questions/tagged/moshi

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github.com/square/moshi @Eric_Cochran github.com/NightlyNexus blog.nightlynexus.com