Upgrading to Moshi Eric Cochran Droidcon Berlin September 5, 2017

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

What is Moshi? JSON serialization library for Java with a streaming and object-mapping API. Gson 2

What is Moshi? JSON serialization library for Java with a streaming and object-mapping API. Gson 2 => “Gson Lite”

Why update from Gson?

Why update from Gson? Gson: - Inactive

Why update from Gson? Gson: - Inactive - Too lenient

Why update from Gson? Gson: - Inactive - Too lenient - Large API

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

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

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

Moshi optimizations Share buffer segments with other Okio users.

Moshi optimizations Avoid allocating strings while deserializing. JsonReader.selectName(Options)

How to Upgrade

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

Reflective field naming policy @SerializedName(“the_name”) => @Json(name = “the_name”)

Reflective field naming policy @SerializedName(“the_name”) => @Json(“the_name”) Prefer using the domain’s naming convention.

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

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

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

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

Object Mapping TypeAdapter => JsonAdapter

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

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

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

Object Mapping without bad leniency Platform types require explicitly registered JsonAdapters. moshi.adapter(java.util.Date.class) moshi.adapter(java.util.ArrayList.class) moshi.adapter(android.graphics.Point.class)

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

Object Mapping No JsonSerializer, JsonDeserializer! These did not stream. TypeAdapter, TypeAdapterFactory => JsonAdapter, JsonAdapter.Factory

Object Mapping TypeToken => com.squareup.moshi.Types factory methods Moshi prefers plain Java’s java.lang.reflect.Type. TypeToken.getParameterized(List.class, String.class) => Types.newParameterizedType(List.class, String.class)

Object Mapping: Unknown Enums enum Exercise { RUN, JUMP, WALK } Gson: exerciseTypeAdapter.fromJson(“jog”) == null Moshi: exerciseJsonAdapter.fromJson(“jog”) => throws JsonDataException

Object Mapping: Unknown Enums enum Exercise { RUN, JUMP, WALK } Gson: exerciseTypeAdapter.fromJson(“jog”) == null Moshi: exerciseJsonAdapter.fromJson(“jog”) => throws JsonDataException EnumWithDefaultValueJsonAdapter: https://goo.gl/85U7Pu API in Moshi to have fallback enums?

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

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

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

Object Mapping: 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) {...} } } }

Object Mapping: 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) {...} } } }

Object Mapping: 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) {...} } } }

Object Mapping: 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) {...} } } } => class PointJsonAdapter { @FromJson Point fromJson(JsonReader reader) {...} @ToJson void toJson(JsonWriter writer, Point value) {...} }

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

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

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

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

Polymorphic types Gson: JsonElement (JsonObject, JsonArray, String, primitives) Moshi: Object (Map, List, String, primitives)

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); // ... } }

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); // ... } }

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); // ... } }

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); // ... } }

Polymorphic types Gson: RuntimeTypeAdapterFactory Moshi: ???

Updating Piecemeal

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. }

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); } }

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(); } }

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

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