@NonNull support for fields

[Turbo87]

It would be cool if Moshi would throw an exception if a field was annotated with @NonNull but fromJson() would assign null to it.

[JakeWharton]

You can do this yourself!

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);
    }
  }
}

Putting validation inside Moshi is a dangerous precedent since it has no end to the types of validation people want.

[Turbo87]

Ah cool, I didn't know that was possible. I guess that's one more reason for a recipe/samples project or webpage.

[JakeWharton]

Yep! That'd make for a good one. I don't think you're the first to ask
about it.

On Thu, Sep 10, 2015 at 4:36 PM Tobias Bieniek notifications@github.com
wrote:

Ah cool, I didn't know that was possible. I guess that's one more reason
for a recipe/samples project or webpage.

—
Reply to this email directly or view it on GitHub
#77 (comment).

[Turbo87]

@JakeWharton I just tried your code but it didn't seem to work as I had expected. What I tried was roughly the following:

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("{}");

I was expecting that the second fromJson() call would throw the IllegalStateException, but it basically worked just like before. From my limited debugging it seems like the NonNullJsonAdapterFactory#create() method gets the annotations of the TestModel class itself (annotations parameter is empty), but not of its members, so annotating the members doesn't seem to have any effect.

Am I missing something?

[swankjesse]

I think it's the difference between rejecting null values and requiring non-null values. The example doesn't do anything about absent keys!

[Turbo87]

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

the above call is not throwing anything either...

but you are right, what I actually want to test is whether the API response included the field and that it is non-null.