The question is published on by Tutorial Guruji team.
I’m planning to use Lombok for creating hundreds of classes that are based on “value object” pattern as follows:
@Data
public final class SomeId implements Serializable {
private final long value;
}
And I want to use these classes for JSON serialization powered by Jackson. for example, consider a DTO class as follows:
public class SomeDTO {
SomeId id;
public SomeId getId() {
return id;
}
}
I want that DTO class to be serialized as something like {"id":123}, but Jackson produces something like {"id":{"value":123}}, which comes with unnecessary nested object with a field named value. i.e. a testcase expresses my requirement:
public class SomeDTOTest {
@Test
public void serializationTest() throws Exception {
SomeDTO dto = new SomeDTO();
dto.id = new SomeId(123);
String serialized = new ObjectMapper().writeValueAsString(dto);
System.out.println(serialized); // {"id":{"value":123}}
assertThat(serialized, is("{"id":123}")); // I want {"id":123} instead!
}
}
I know putting @JsonValue annotation to every getValue() method in SomeId classes would be a solution, but I can’t do it because there is no actual definition of @Data classes because Lombok automatically creates it.
Creating actual getValue() method annotated as @JsonValue for every classes by hand might be another solution but it means creating tons of boilarplate code.
How do I achieve this requirement without boilerplate code?
Answer
You can write custom Serializer for this class.
E.g.:
class CustomSerializer extends StdSerializer<SomeId>{
protected CustomSerializer(Class<SomeId> t) {
super(t);
}
@Override
public void serialize(SomeId someId, JsonGenerator gen, SerializerProvider serializers)
throws IOException, JsonProcessingException {
gen.writeNumber(someId.getValue());
}
}
Now use this serializer to serialize SomeId class:
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addSerializer(new CustomSerializer(SomeId.class));
mapper.registerModule(module);
SomeDTO dto = new SomeDTO();
dto.id = new SomeId(123);
String serialized = mapper.writeValueAsString(dto);
System.out.println(serialized); // output : {"id":123}