How to get Java's object field's name from JSON fields name

Question

I want to filter out some fields in the response. Filtering should be done before the Java object is serialised into the JSON. Consider:

public class Entity {

    @JsonProperty("some_property")
    String someProperty;

    @JsonProperty("nested_entity")
    @OneToMany(mappedBy = "entity", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    NestedEntity nestedEntity;

    // other fields for eg fieldA, fieldB
}

API endpoint

get api/entity/{id}?fields=some_property,field_a

Now the ask is, in the o/p we should filter out only someProperty and fieldA. Like

{
    "some_property": "foo",
    "field_a": "bar"
}

But since these are JSON fields not Java object fields I can't filter or get these fields them by Reflection. Is there a way we can achieve this, i.e. filtering of Java object based on json fields ?

FYI: The advantage of filtering before serialization is that the lazy-fields' DB calls are saved unless these fields are required

Thanks in advance!

See about @JsonFilter. You can apply filtering at serialization. — Cimon
– Cimon, Commented Oct 15, 2020 at 20:01

NiksVij · Accepted Answer · 2020-10-17 16:21:46Z

On the suggestion of @robocode using @JsonFilter and also to support empty fields or no fields filtering added JacksonConfiguration

@JsonFilter("entityFilter")
public class Entity {

    @JsonProperty("some_property")
    String someProperty;
    // other fields for eg fieldA, fieldB
}

@Configuration
public class JacksonConfiguration { 
    public JacksonConfiguration(ObjectMapper objectMapper) {
        objectMapper.setFilterProvider(new SimpleFilterProvider().setFailOnUnknownId(false));
    } 
}

public class FieldMapper {
    
    @SneakyThrows
    public static Dto getFilteredFields(Dto make, String fields[]) {
        ObjectMapper objectMapper = new ObjectMapper();
        if(ArrayUtils.isNotEmpty(fields)) {
            FilterProvider filters = new SimpleFilterProvider().addFilter(
                    "entityFilter", SimpleBeanPropertyFilter.filterOutAllExcept(fields)
            );
            objectMapper.setFilterProvider(filters);
        } else {
            objectMapper.setFilterProvider(new SimpleFilterProvider().setFailOnUnknownId(false));
        }
        JsonNode j = objectMapper.readTree(objectMapper.writeValueAsString(make));
        return objectMapper.convertValue(j, Dto.class);
    }
}

// controller code to get the dto for api/entity/{id}?fields=some_property,field_a
Dto filteredFields = getFilteredFields(dto, fields);
return filteredFields

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