The wonders you can do with Moshi

Moshi is as very powerful and yet lightweight modern JSON library for Android and Java. It understands primitives and objects, Strings and enums, arrays and java’s build-int collections (such as Lists, Sets and Maps), at the same time providing a nice api for serialization/deserialization customization.

These slide are for my BarCamp Talk at DroidconUK 2016.
Include:
- Short intro to square/moshi
- Example for a complex custom adapter
- Reference to Moshi-Auto-Value & Moshi-Lazy-Adapters

Transcript

1. The  wonders  you  can  do  with   Moshi @SerjLtt
2. Some  specs • JSON  serialisation/de-­‐serialisation   • Based  on  Okio   ➡ Works  with  Source/Sink  not  java.io.*Stream   ➡ Avoids  unnecessary  buffering   • JsonReader/JsonWriter   • JsonAdapter
3. JsonAdapter abstract T fromJson(JsonReader reader) throws IOException; abstract void toJson(JsonWriter writer, T value) throws IOException; @FromJson - Any method that accepts an object / JsonReader @ToJson - Any method that accepts an Object / JsonWriter
4. JsonAdapter.Factory public interface Factory { JsonAdapter<?> create(Type type, Set<? extends Annotation> annotations, Moshi moshi); } • Called by Moshi#nextAdapter() • All JsonAdapter’s are retrieved via their respective factories! • Order matters!
5. So  what? { "name": "Pikachu", "weight": 3.45, "stats": {}, "is_buddy": true }
6. So  what? { "response": { "pokemon": [ { "name": "Pikachu", "weight": 3.45, "stats": {}, "is_buddy": true } ] } }
7. @JsonQualifier  to  the  rescue • Allows to annotate a custom annotation that will be backed by a JsonAdapter. • Custom Annotations should be used for fields/methods/params ➡ Moshi doesn’t search for type annotations! • The adapters factory much check for the presents of the annotation • or, it should be used in a @FromJson/@ToJson annotated method
8. So  let’s  fix  it @Documented
 @JsonQualifier
 @Retention(RetentionPolicy.RUNTIME)
 @Target({ ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER })
 public @interface Wrapped {
 /** The path to the wrapped json value. */
 String[] value();
 }
9. So  let’s  fix  it public static final JsonAdapter.Factory FACTORY = (type, annotations, moshi) -> {
 Annotation annotation = findAnnotation(annotations, Wrapped.class);
 if (annotation == null) return null;
 
 Set<? extends Annotation> reducedAnnotations = new LinkedHashSet<>(annotations);
 reducedAnnotations.remove(annotation);
 
 Wrapped wrapped = (Wrapped) annotation;
 return new WrappedJsonAdapter<>(moshi.adapter(type, reducedAnnotations), wrapped.value()); };
10. So  let’s  fix  it @GET("/buddy")
 @Wrapped({"response", "pokemon"}) Call<List<Pokemon>> getBuddy();
11. So  what? { "response": { "pokemon": [ { "name": "Pikachu", "weight": 3.45, "stats": {}, "is_buddy": true } ] } }
12. So  let’s  fix  it @Documented
 @JsonQualifier
 @Retention(RetentionPolicy.RUNTIME)
 @Target({ ElementType.FIELD, ElementType.METHOD })
 public @interface FirstElement {
 }
13. So  let’s  fix  it @Override public T fromJson(JsonReader reader) throws IOException {
 List<T> fromJson = adapter.fromJson(reader);
 if (fromJson != null && !fromJson.isEmpty()) return fromJson.get(0);
 return null;
 }
 
 @Override public void toJson(JsonWriter writer, T value) throws IOException {
 adapter.toJson(writer, Collections.singletonList(value));
 }
14. So  let’s  fix  it @GET("/buddy")
 @Wrapped({"response", “pokemon"}) @FirstElement Call<Pokemon> getBuddy();
15. Good  to  Know’s • Auto-­‐Value-­‐Moshi     https://github.com/rharter/auto-­‐value-­‐moshi   • Moshi-­‐Lazy-­‐Adapters   https://github.com/serj-­‐lotutovici/moshi-­‐lazy-­‐adapters
16. Thanks! @SerjLtt