Jackson ObjectMapper - specify serialization order of object properties

Question

I\'m implementing a RESTful web service where user has to send a signed verification token along with the request so that I could ensure that the request has not been tamper

Answer 1

In Jackson 2.x, which you are probably using today, use:

ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true);

If you care about looks, you may also consider SerializationFeature.INDENT_OUTPUT as well.

Note that you must serialize Maps or Objects for this to sort correctly. If you serialize a JsonNode for example (from readTree), that won't be properly indented.

Example

import com.fasterxml.jackson.databind.*;

ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true);
mapper.configure(SerializationFeature.INDENT_OUTPUT, true);

String input = "{\"hello\": {\"cruel\" : \"world\"} }";
Object pojo = mapper.readValue(input, Object.class);
System.out.println(mapper.writeValueAsString(pojo));

results in:

{
  "hello" : {
    "cruel" : "world"
  }
}

Answer 2

You can use mix-in and specify the order of properties as you like:

import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import com.fasterxml.jackson.databind.ObjectMapper;

import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;

@Component
public final class ObjectMapperUtils {

    private static final ObjectMapper MAPPER = new ObjectMapper();

    static {
        MAPPER.addMixIn(Object.class, IdFirst.class);
    }

    @Bean
    public ObjectMapper objectMapper() {
        return MAPPER;
    }

    @JsonPropertyOrder({"id", "...", "..."})
    private abstract static class IdFirst {}

}

Answer 3

Instead of using flag argument:

objectMapper.enable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY);

Answer 4

The annotations are useful, but can be a pain to apply everywhere. You can configure your whole ObjectMapper to work this way with

Current Jackson versions: objectMapper.configure(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY, true)

Older Jackson versions: objectMapper.configure(SerializationConfig.Feature.SORT_PROPERTIES_ALPHABETICALLY, true);

Answer 5

From Duncan McGregor's answer: Its better to use it like this:

objectMapper.configure(SerializationConfig.Feature.SORT_PROPERTIES_ALPHABETICALLY, true);

as MapperFeature is for XMLs and comes with jackson-databind which is not required...

Answer 6

The following 2 ObjectMapper configuration are required:

ObjectMapper.configure(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY, true)
or
ObjectMapper.enable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY)

defines the property serialization order used for POJO fields
Note: does not apply to java.util.Map serialization!

and

ObjectMapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true)
or
ObjectMapper.enable(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS)

Feature that determines whether java.util.Map entries are first sorted by key before serialization

---

Spring Boot config example (yaml):

spring:
  jackson:
    mapper:
      SORT_PROPERTIES_ALPHABETICALLY: true
    serialization:
      ORDER_MAP_ENTRIES_BY_KEYS: true