PropertyNamingStrategy doesn't work during deserialization

[unlimitedsola]

simple kotlin snippet to reproduce:

class JacksonTest {

    @Test
    fun testSnakeCaseDeserialization() {
        val json = """{"my_camel_case":10001}"""
        val objectMapper = jacksonObjectMapper().findAndRegisterModules()
        val obj = objectMapper.readValue<TestSnakeCase>(json)
        println(obj)
        assertEquals(10001, obj.myCamelCase)
    }

    @Test
    fun testSnakeCaseSerialization() {
        val objectMapper = jacksonObjectMapper().findAndRegisterModules()
        val obj = TestSnakeCase(10001)
        println(objectMapper.writeValueAsString(obj))
    }

    @JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy::class)
    data class TestSnakeCase(val myCamelCase: Int)
}

also happens in Java

[cowtowncoder]

Please re-file at Kotlin module unless reproducible with Java-only test. If latter, please update with Java-only example here and I can have a look.

[unlimitedsola]

@cowtowncoder Sorry for that I thought kotlin code may contain less boilerplate code
Here is a test case in Java

public class JacksonJavaTest {

    @Test
    public void testSnakeCaseDeserialization() throws IOException {
        String json = "{\"my_camel_case\":10001}";
        ObjectMapper objectMapper = new ObjectMapper().findAndRegisterModules();
        TestSnakeCase obj = objectMapper.readValue(json, TestSnakeCase.class);
        assertEquals(Integer.valueOf(10001), obj.getMyCamelCase());
    }

    @Test
    public void testSnakeCaseSerialization() throws JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper().findAndRegisterModules();
        TestSnakeCase obj = new TestSnakeCase(10001);
        System.out.println(objectMapper.writeValueAsString(obj));
    }

    @JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy.class)
    static class TestSnakeCase {
        private Integer myCamelCase;

        @JsonCreator
        public TestSnakeCase(Integer myCamelCase) {
            this.myCamelCase = myCamelCase;
        }

        public Integer getMyCamelCase() {
            return myCamelCase;
        }

        public void setMyCamelCase(Integer myCamelCase) {
            this.myCamelCase = myCamelCase;
        }
    }

}

[unlimitedsola]

It looks like the PropertyNamingStrategy only works with no-arg-constructor because the following test won't fail:

public class JacksonJavaTest {

    @Test
    public void testSnakeCaseDeserialization() throws IOException {
        String json = "{\"my_camel_case\":10001}";
        ObjectMapper objectMapper = new ObjectMapper().findAndRegisterModules();
        TestSnakeCase obj = objectMapper.readValue(json, TestSnakeCase.class);
        assertEquals(Integer.valueOf(10001), obj.getMyCamelCase());
    }

    @Test
    public void testSnakeCaseSerialization() throws JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper().findAndRegisterModules();
        TestSnakeCase obj = new TestSnakeCase(10001);
        System.out.println(objectMapper.writeValueAsString(obj));
    }

    @JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy.class)
    static class TestSnakeCase {
        private Integer myCamelCase;

        public TestSnakeCase() {
        }

        public TestSnakeCase(Integer myCamelCase) {
            this.myCamelCase = myCamelCase;
        }

        public Integer getMyCamelCase() {
            return myCamelCase;
        }

        public void setMyCamelCase(Integer myCamelCase) {
            this.myCamelCase = myCamelCase;
        }
    }

}

[cowtowncoder]

Actually I think problem here could be bit different.

But first the usual question: which version is this with? Is it reproducible on 2.9.2?
(there were changes in 2.9.2 in this are I think)

If yes, does using

@JsonCreator(mode = JsonCreator.Mode.PROPERTIES)

make difference? It should as by default I think mode would be auto-detected as Mode.DELEGATING (since it is exactly one argument and no property name is defined).

[unlimitedsola]

Oops, This is interesting, I didn't notice it only happens on POJO that has exactly one property.
add @JsonCreator(mode = JsonCreator.Mode.PROPERTIES) and everything works fine. Thanks!

[cowtowncoder]

@unlimitedsola Yes this is.... sort of unfortunate thing, and commonly stumbled upon. So there are two interpretations here: with just 1 property, one could either consider mapping exact value ("delegating"), or JSON Object of just one property ("property-based"). Jackson tries to use heuristics if not explicitly specified but I don't think there is anything that can ultimately tell it, short of allowing configuration for defaulting (mode used if not annotated) and allowing overrides.

mode property was added to allow explicit annotation: if you had added explicit name annotation with @JsonProperty this would also have happened. It is only ambiguous if name is derived from bytecode.