Using a delegating deserializer with StdValueInstantiator

[Steve Bread]

Hi, I'm using a delegating deserializer with java.util.Date as the delegate type and my class 'CustomDate' as the target type. I want to apply this deserializer to a constructor argument in conjunction with a ValueInstantiator. I got it to work but I would like to know if there is a simpler way.

Delegating deserializer with java.util.Date as delegate type:

   public class CustomDateDeserializer extends StdDelegatingDeserializer<CustomDate>
   {
      public CustomDateDeserializer() {
         super(new StdConverter<Date, CustomDate>() { ... });
      }
     
      public CustomDateDeserializer(Converter<?, CustomDate> converter,
                                    JavaType delegateType,
                                    JsonDeserializer<?> delegateDeserializer) { ... }
      }
      // other content omitted
   }

POJO:

   @JsonValueInstantiator(value = TestInstantiator.class)
   public class Test{
      public Test(CustomDate customDate) {
      }
      // rest omitted
   }

ValueInstantiator:

   public class TestInstantiator extends StdValueInstantiator
   {
      public boolean canCreateFromObjectWith() {
         return true;
      }

      public SettableBeanProperty[] getFromObjectArguments(DeserializationConfig config) {
         CreatorProperty customDate = new CreatorProperty(new PropertyName("customDate"),
                                            config.constructType(CustomDate.class), null, null,
                                            null, null, 0, null, PropertyMetadata.STD_REQUIRED)
                                      .withValueDeserializer(new CustomDateDeserializer());
         return new CreatorProperty[] { customDate };
      }

      @Override
      public Object createFromObjectWith(DeserializationContext ctxt, Object[] args) throws IOException, JsonProcessingException {
         return new Test((CustomDate) args[0]);
      }
   }

Creating a Test instance fails with a NPE because the values for _delegateType and _delegateDeserializer in StdDelegatingDeserializer are null. These values are set by Jackson when deserializing a property of type CustomDate but are not set automatically when deserializing the constructor argument.
    
To resolve this, I have to use a fully initialized delegating deserializer in TestInstantiator

      new CustomDateDeserializer(new StdConverter<Date, CustomDate>() { ... },
                                 config.constructType(Date.class),
                                 new DateDeserializers.DateDeserializer());

Is this the correct way to do it or is there way to set up the CreatorProperty such that Jackson will set the delegateType and delegateDeserializer as it does for properties?

I set up a module with
   addDeserializer(CustomDate.class, new CustomDateDeserializer());
but Jackson does not associate the constructor argument with the custom deserializer and that's why I have to specify the deserializer explicitly for CreatorProperty.

Thanks.

[Tatu Saloranta]

Actually you should not have to use ValueInstatiator here; custom deserializer should be used just fine for anything declared as CustomDate. So defined constructor like so:

  @JsonCreator

  Test(@JsonProperty("customDate") CustomDate d) {
       ...
  }

should work. If not, you could file an issue, preferably with a simplified unit test / code sample to reproduce.

As to delegating deserializer code seems fine, but you could also use annotations on CustomDate type, like so:

@JsonDeserializer(converter=MyConverter.class)

public class CustomDate {
    ...
}

which is slightly simpler with less code and no need for explicit registration. But it also adds direct dependency to jackson annotation from class, which some developers dislike.

-+ Tatu +-

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[Steve Bread]

Thanks Tatu. Unfortunately I cannot use JsonCreator because the ValueInstantiator actually doesn't create the instance directly but uses a service; I was trying to simplify it for the example. The method is actually

   public Object createFromObjectWith(DeserializationContext ctxt, Object[] args) throws IOException, JsonProcessingException {

      return testService.create((CustomDate) args[0]);
   }

Thanks very much for confirming the code usage. I wasn't aware that I could define the converter with @JsonDeserialize. That's very convenient and I'll see if I can use it here or in the future.

Thanks!
Steve