@JsonDeserialize prioritized over addDeserializer

[JanStureNielsen]

Using Jackson Databind 2.13.5, annotating a POJO with @JsonDeserialize:

@Getter
@Builder
@ToString
@JsonDeserialize(builder=Person.PersonBuilder.class)
static class Person {
    private final String name;
    private final List<Pet> pets;

}

@Getter
@Builder
@ToString
static class Pet {
    private final String name;
    private final String type;

}

takes priority over an explicitly configured deserializer in a mapper:

String serializedPersons = """
name,pets
Ali,"[{'Cutesy','cat'}, {'Tootsie','cat'}]"
Jan,"[{'Mr. Bubbles','dog'}, {'Lilly','cat'}]"
Tom,"[{'Fester','dog'}, {'Wednesday','cat'}]"
Zoe,"[{'Jaeger','dog'}, {'Deira','cat'}]"
""";

CsvMapper mapper = new CsvMapper();
SimpleModule module = new SimpleModule();

module.addSerializer(Person.class, new PersonSerializer());
module.addDeserializer(Person.class, new PersonDeserializer());

mapper.registerModule(module);

CsvSchema schema = mapper.schemaFor(Person.class).withHeader();
ObjectReader reader = mapper.readerFor(Person.class).with(schema);

MappingIterator<Person> i = reader.readValues(serializedPersons);

while (i.hasNext()) {
    System.out.println("Person: " + i.next());
}

It seems like explicitly configured serializers & deserializers on the mappers should take precedence over others that are discovered.

In my case, I have network marshalled objects that should be using annotated builder, and CLI applications that should be using their own explicitly configured deserializers. I wrote a question on SO before I found the problem.

---

public class JacksonTest {
    @Test
    public void writeJson() throws JsonProcessingException {
        var mapper = new ObjectMapper();
        var writer = mapper.writer();

        System.out.println(writer.writeValueAsString(_single()));
        System.out.println(writer.writeValueAsString(_multiple()));
    }

    @Test
    public void writeJsonObjectsIndividually() throws IOException {
        var mapper = new ObjectMapper();
        var writer = new StringWriter();

        try (var seqWriter = mapper.writerFor(Person.class).writeValues(writer)) {
            seqWriter.write(_single());
            seqWriter.writeAll(_multiple());
        }
        System.out.println(writer.toString());
    }

    @Test
    public void writePersonToCsv() throws IOException {
        CsvMapper mapper = new CsvMapper();
        SimpleModule module = new SimpleModule();

        module.addSerializer(Person.class, new PersonSerializer());
        module.addDeserializer(Person.class, new PersonDeserializer());

        mapper.registerModule(module);
        var writer = new StringWriter();

        CsvSchema schema = mapper.schemaFor(Person.class)
                .withHeader();

        try (var seqWriter = mapper.writerWithSchemaFor(Person.class).with(schema).writeValues(writer)) {
            seqWriter.write(_single());
            seqWriter.writeAll(_multiple());
        }
        System.out.println(writer.toString());
    }

    @Test
    public void deserializePets() {
        String serializedPets = "[{'Mr. Bubbles','dog'}, {'Lilly','cat'}]";

        List<Pet> pets = PersonDeserializer.deserialize(serializedPets);

        assertThat(pets).hasSize(2);
    }

    @Test
    public void readPersonFromCsv() throws IOException {
        String serializedPersons = """
        name,pets
        Ali,"[{'Cutesy','cat'}, {'Tootsie','cat'}]"
        Jan,"[{'Mr. Bubbles','dog'}, {'Lilly','cat'}]"
        Tom,"[{'Fester','dog'}, {'Wednesday','cat'}]"
        Zoe,"[{'Jaeger','dog'}, {'Deira','cat'}]"
        """;

        CsvMapper mapper = new CsvMapper();
        SimpleModule module = new SimpleModule();

        module.addSerializer(Person.class, new PersonSerializer());
        module.addDeserializer(Person.class, new PersonDeserializer());

        mapper.registerModule(module);

        CsvSchema schema = mapper.schemaFor(Person.class).withHeader();
        ObjectReader reader = mapper.readerFor(Person.class).with(schema);

        MappingIterator<Person> i = reader.readValues(serializedPersons);

        while (i.hasNext()) {
            System.out.println("Person: " + i.next());
        }
    }

    @Getter
    @Builder
    @ToString
    //This will take precedence over mapper registered deserializers
    @JsonDeserialize(builder=Person.PersonBuilder.class)
    static class Person {
        private final String name;
        private final List<Pet> pets;

    }

    @Getter
    @Builder
    @ToString
    static class Pet {
        private final String name;
        private final String type;

    }

    static class PersonSerializer extends StdSerializer<Person> {
        private static final long serialVersionUID = 1L;

        public PersonSerializer() {
            this(Person.class);
        }

        public PersonSerializer(Class<Person> type) {
            super(type);
        }

        @Override
        public void serialize(Person value, JsonGenerator jgen, SerializerProvider provider)
          throws IOException, JsonProcessingException {
            jgen.writeStartObject();
            jgen.writeStringField("name", value.getName());
            jgen.writeStringField("pets", _toString(value.getPets()));
            jgen.writeEndObject();
        }

        private String _toString(List<Pet> pets) {
            return Arrays.toString(pets.stream()
                    .map(PersonSerializer::serialize)
                    .toArray(String[]::new));
        }

        private static String serialize(Pet pet) {
            return String.format("{'%s','%s'}", pet.name, pet.type);
        }

    }

    static class PersonDeserializer extends StdDeserializer<Person> {
        private static final long serialVersionUID = 1L;

        public PersonDeserializer() {
            this(Person.class);
        }

        public PersonDeserializer(Class<Person> type) {
            super(type);
        }

        @Override
        public Person deserialize(JsonParser p, DeserializationContext ctxt)
          throws IOException, JsonProcessingException {
            JsonNode node = p.getCodec().readTree(p);

            String name = node.get("name").asText();
            String petsSerialized = node.get("pets").asText();

            List<Pet> pets = deserialize(petsSerialized);

            return Person.builder().name(name).pets(pets).build();
        }

        private static List<Pet> deserialize(String serializedPets) {
            return Arrays.stream(serializedPets.replaceAll("^.\\{?|}?.$", "").split("},\s*\\{"))
                    .map(inner -> Arrays.stream(inner.replaceAll("^.'?|'?.$", "").split("','")).toList())
                    .map(l -> deserialize(l))
                    .collect(Collectors.toList());
        }

        private static Pet deserialize(List<String> l) {
            return Pet.builder().name(l.get(0)).type(l.get(1)).build();
        }
    }

    private static Person _single() {
        return Person.builder().name("Jan").pets(List.of(Pet.builder().name("Mr. Bubbles").type("dog").build(), Pet.builder().name("Lilly").type("cat").build())).build();
    }

    private static Person[] _multiple() {
        return List.of(_single(), _single(), _single()).toArray(Person[]::new);
    }

}

[JanStureNielsen]

Whoops -- wrong repo