@JsonDeserialize(contentUsing=...) is ignored if content type is determined by @JsonTypeInfo

Tested versions: 2.9.0.pr3, 2.8.8 and 2.0.1

Expected behavior: Jackson respects @JsonDeserialize(contentUsing=...) even if the content’s type is determined via @JsonTypeInfo. Actual behavior: @JsonDeserialize(contentUsing=...) is ignored.

The following example demonstrates the issue. The expected output is “ok”. The observed output is empty. BarDeserializer is never called (nor constructed for that matter).

Removing the @JsonTypeInfo line “fixes” the example.

public class Test {
  static class BarDeserializer extends JsonDeserializer<Bar> {
    @Override
    public Bar deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
      System.out.println("ok");
      return p.readValueAs(Bar.class);
    }
  }

  @JsonTypeInfo(use = JsonTypeInfo.Id.NAME)
  static class Bar {
    public int dummy;
  }

  static class Foo {
    @JsonDeserialize(contentUsing = BarDeserializer.class)
    public List<Bar> bars;
  }

  public static void main(String[] args) throws IOException {
    Foo foo = new Foo();
    foo.bars = Arrays.asList(new Bar());

    ObjectMapper om = new ObjectMapper();
    om.readValue(om.writeValueAsString(foo), Foo.class);
  }
}

[pdegoeje]

@james-woods I ended up with something like the following:

  static class BarListDeserializer extends JsonDeserializer<List<Bar>> {
    @Override
    public List<Bar> deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
      List<Bar> barList = jsonParser.readValueAs(new TypeReference<List<Bar>>() { });
      // do post-processing
      return barList;
    }
  }

  static class Foo {
    // Use a custom deserializer for the entire list, instead of a per element deserializer.
    @JsonDeserialize(using = BarListDeserializer.class)
    public List<Bar> bars;
  }

For my use case, registering a list of polymorphic typed objects so they could be referenced by constructors from objects later in the same json file, this was sufficient.

[pdegoeje]

Yeah I worked around it by writing a custom deserializer for the entire list, which is basically a single line of extra code.

Perhaps this behavior could be documented in the mean time, because it isn’t immediately obvious (to me at least) why contentUsing isn’t compatible with polymorphic types.