@NonNull support for fields about moshi HOT 6 CLOSED

public final class NonNullJsonAdapterFactory implements JsonAdapter.Factory {
  @Override
  public JsonAdapter<?> create(Type type, Set<? extends Annotation> annotations, Moshi moshi) {
    for (Annotation annotation : annotations) {
      if ("NonNull".equals(annotation.getClass().getSimpleName())) { // Or NonNull.class.equals(..)
        JsonAdapter<Object> delegate = moshi.nextAdapter(this, type, annotations);
        return new NonNullJsonAdapter<>(delegate);
      }
    }
    return null;
  }

  static class NonNullJsonAdapter<T> extends JsonAdapter<T> {
    private final JsonAdapter<T> delagate;

    NonNullJsonAdapter(JsonAdapter<T> delagate) {
      this.delagate = delagate;
    }

    @Override public T fromJson(JsonReader reader) throws IOException {
      T value = delagate.fromJson(reader);
      if (value == null) {
        throw new IllegalStateException("value was null!");
      }
      return value;
    }

    @Override public void toJson(JsonWriter writer, T value) throws IOException {
      if (value == null) {
        throw new IllegalStateException("value was null!");
      }
      delagate.toJson(writer, value);
    }
  }
}

public static class TestModel {
    @NonNull String a;
    String b;
}

Moshi moshi = new Moshi.Builder()
        .add(new NonNullJsonAdapterFactory())
        .build();

JsonAdapter<TestModel> adapter = moshi.adapter(TestModel.class);

// should work
assertThat(adapter.fromJson("{\"a\":\"test\"}").a).isEqualTo("test");

// should fail
adapter.fromJson("{}");

adapter.fromJson("{\"a\":null}");