Possible 2.16.0 Enum-as-JSON-Object serialization regression

[cowtowncoder]

Discussed in #4563

^{Originally posted by Mugiwara84 June 5, 2024}
Hi,
I am using jackson with spring to serialize a java enumeration which looks like this :

@JsonFormat(shape = JsonFormat.Shape.OBJECT)
public enum Level {
  LEVEL1("level1"),
  LEVEL2("level2"),
  LEVEL3("level3", Level.LEVEL1);

  String label;
  Level sublevel;

.......
}

Before updating to 2.16.0, I was getting this when serializing :

[
  {
    "label": "level1"
  },
  {
    "label": "level2"
  },
  {
    "label": "level3",
    "sublevel": {
        "label": "level1"
    }
  }
]

Since 2.16.0, I'm getting :

[
  {
    "label": "level1"
  },
  {
    "label": "level2"
  },
  {
    "label": "level3"
  }
]

Is this the expected behaviour ?
Is there a different way to achieve the previous result with parameters or annotations ?

[JooHyukKim]

We do need Mapper configuration and rest of the enum declaration, to find out how the sublevel property is ignored, but in LEVEL3 is found.

Meanwhile refer to below failing reproduction.

public class EnumAsFormatObject4564Test
        extends BaseMapTest {

    @JsonFormat(shape = JsonFormat.Shape.OBJECT)
    public enum Level {
        LEVEL1("level1"),
        LEVEL2("level2"),
        LEVEL3("level3", Level.LEVEL1);

        public String label;
        public Level sublevel;

        Level(String level2) {
            this.label = level2;
        }

        Level(String level3, Level level) {
            this.label = level3;
            this.sublevel = level;
        }

    }

    private final ObjectMapper MAPPER = newJsonMapper();

    @Test
    public void testEnumAsFormatObject() throws JsonProcessingException {
        List<Level> levels = new ArrayList<>();
        levels.add(Level.LEVEL1);
        levels.add(Level.LEVEL2);
        levels.add(Level.LEVEL3);

        String JSON = MAPPER.writerFor(new TypeReference<List<Level>>() {
                })
                .writeValueAsString(levels);

        // Fails, because we get [{"label":"level1"},{"label":"level2"},{"label":"level3"}]
        assertEquals("[" +
                "{\"label\":\"level1\"}," +
                "{\"label\":\"level2\"}," +
                "{\"label\":\"level3\",\"sublevel\":{\"label\":\"level1\"}}" +
                "]", JSON);
    }
}

[Mugiwara84]

I do not have Mapper configuration, I am just using Spring which uses jackson when returning response in a controller from a List.

But I did recreate a simple java maven project using this pom :

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>level</groupId>
	<artifactId>level</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<dependencies>
		<dependency>
			<groupId>com.fasterxml.jackson.core</groupId>
			<artifactId>jackson-databind</artifactId>
			<version>2.15.4</version>
		</dependency>
		<dependency>
			<groupId>org.junit.jupiter</groupId>
			<artifactId>junit-jupiter</artifactId>
			<version>5.10.2</version>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.13.0</version>
				<configuration>
					<release>21</release>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>

When I am using your code (except I am not extending BaseMapTest and I add the @JsonInclude(JsonInclude.Include.NON_NULL) annotation) :

import static org.junit.jupiter.api.Assertions.assertEquals;

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.json.JsonMapper;
import java.util.ArrayList;
import java.util.List;
import org.junit.jupiter.api.Test;

public class EnumAsFormatObject4564Test {

  @JsonFormat(shape = JsonFormat.Shape.OBJECT)
  @JsonInclude(JsonInclude.Include.NON_NULL)
  public enum Level {
    LEVEL1("level1"),
    LEVEL2("level2"),
    LEVEL3("level3", Level.LEVEL1);

    public String label;
    public Level sublevel;

    Level(String level2) {
      this.label = level2;
    }

    Level(String level3, Level level) {
      this.label = level3;
      this.sublevel = level;
    }
  }

  private final ObjectMapper MAPPER = new JsonMapper();

  @Test
  public void testEnumAsFormatObject() throws JsonProcessingException {
    List<Level> levels = new ArrayList<>();
    levels.add(Level.LEVEL1);
    levels.add(Level.LEVEL2);
    levels.add(Level.LEVEL3);

    String JSON = MAPPER.writerFor(new TypeReference<List<Level>>() {}).writeValueAsString(levels);

    // Fails, because we get [{"label":"level1"},{"label":"level2"},{"label":"level3"}]
    assertEquals(
        "["
            + "{\"label\":\"level1\"},"
            + "{\"label\":\"level2\"},"
            + "{\"label\":\"level3\",\"sublevel\":{\"label\":\"level1\"}}"
            + "]",
        JSON);
  }
}

The test is ok. But when I update njackson-databind to 2.16.0 or 2.17.1, the test fails, it returns :
[{"label":"level1"},{"label":"level2"},{"label":"level3"}]

[pjfanning]

There are some changes in the EnumSerializer for Jackson 2.16 - eg #4039

[JooHyukKim]

This is regression created by #3832 which improved handling of Enum's via Annotated, not direct class declaration.

This check in Method _removeEnumSelfReferences()
below did not count for having Enum having itself as a field.

jackson-databind/src/main/java/com/fasterxml/jackson/databind/ser/BasicSerializerFactory.java

Line 1246 in fc67817

if (propType.isEnumType() && propType.isTypeOrSubTypeOf(aClass)) {

.

[JooHyukKim]

Filed a fix PR #4565 against 2.16 version.

[cowtowncoder]

@JooHyukKim if you think this is safe enough against 2.16 that works (and 2.16 is still open until 2.18.0 release, as per https://github.com/FasterXML/jackson/wiki/Jackson-Releases).

I will try to get PR reviewed and merged soon.

[cowtowncoder]

Fixed in 2.16 (for potential 2.16.3 release) and onwards (2.17.2, 2.18.0).

[Mugiwara84]

Thank you !

[px100]

@cowtowncoder when can we expect a release with this fix ?

[cowtowncoder]

@px100 I am planning to release 2.17.2 today if all goes well.