Change in behavior in Jackson Databind 2.19.x

[erizzo-cfa]

It seems that Jackson 2.19.x has changed the way @JsonProperty is treated when applied to enums. Here's a simple test to demonstrate:

import static org.assertj.core.api.Assertions.assertThat;
import org.junit.jupiter.api.Test;

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

class EnumJsonPropertyTest {

	static enum Color {
		@JsonProperty
		Red,
		Blue,
		Green
	}


	static class Thing {
		Color color;

		public void setColor(Color newValue) { this.color = newValue; }
		public Color getColor() { return color; }
	}

	@Test
	void withEnumName() throws JsonProcessingException {
		ObjectMapper mapper = new ObjectMapper();
		String json = """
				{"color": "Red"}
				""";
		Thing thing = mapper.readValue(json, Thing.class);

		assertThat(thing.getColor()).isEqualTo(Color.Red);
	}

	@Test
	void withBlank() throws JsonProcessingException {
		ObjectMapper mapper = new ObjectMapper();
		String json = """
				{"color": ""}
				""";
		Thing thing = mapper.readValue(json, Thing.class);

		assertThat(thing.getColor()).isEqualTo(Color.Red);
	}
}

With jackson-databind 2.18.4, the test withBlank() fails and withEnumName() passes.
With 2.19.0/2.19.1, it's the other way around, withEnumName() fails and withBlank() passes.

Was this change intentional? According to the Javadoc of @JsonProperty, it seems like the behavior of 2.18.4 was actually incorrect, but I didn't see any mention of a bug like that in the release notes.

[cowtowncoder]

This example seems to use Lombok -- we can't use it as-is. But could you de-Lombok it? That would show actual annotations and methods.

[cowtowncoder]

FWTW, with a quick look & ref to semantics, 2.18.4 behavior seems more correct.

One thing you probably could try is see how Red is serialized: that indicates configured enum serialization.

[erizzo-cfa]

FWTW, with a quick look & ref to semantics, 2.18.4 behavior seems more correct

I just noticed this in the Javadocs (when using 2.19):

NOTE: for Enums, empty String is a valid value (and missing value is taken as empty String), unlike for regular properties, and does NOT mean "use default Enum name". (handling fixed in Jackson 2.19)

[erizzo-cfa]

Also: what is the point of using @JsonProperty like so:

enum Color {
  @JsonProperty
  Red,
  Blue,
  Green
}

I'm not sure of the intent. I work on a team supporting a lot of other teams/applications, so I'm trying to get an answer as to the intent of that usage of @JsonProperty. I've never seen it used on an enum like that myself.

[cowtowncoder]

Sigh. Ok, my spider sense tingling was right. Apparently this was intentional... seems incorrect in hindsight but... it is what it is. Will close the issue I just created.

[erizzo-cfa]

This example seems to use Lombok -- we can't use it as-is.

I updated the code to remove Lombok usage.

[cowtowncoder]

Note: created #5219 for apparent regression.