Jackson库：JSON元素中Java对象的自定义映射

Question

I have two class

public class Person {
    private long id;
    private String name;
    private Gender gender;

    // getter and setter omitted
}

and

public class Gender {
    private long id;
    private String value;

    // getter and setter omitted
}

By default the JSON mapping with Jackson library of a Person object is:

{
   id: 11,
   name: "myname",
   gender: {
      id: 2,
      value: "F"
   }
}

I'd like to known how to configure Jackson to obtain:

{
   id: 11,
   name: "myname",
   gender: "F"
}

I don't want mapping all the Gender object but only its value property.

Answer 1

You can use a custom serializer:

    public class GenderSerializer extends JsonSerializer<Gender> {

        public GenderSerializer() {
        }

        @Override
        public void serialize(Gender gender, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
               jgen.writeString(gender.getValue());        
        }
    }

And in your Person class:

public class Person {
    private long id;
    private String name;
    @JsonSerialize(using = GenderSerializer.class)
    private Gender gender;

}

Answer 2

you might wanna see this for custom mapping OR if you need a short cut then you can change getter/setter of gender like this

public String getGender(String type){
  this.getGender().getValue();
}
public void setGender(String value){
  Gender gender = new Gender();
  gender.setId(2);
  gender.setValue(value);
  this.gender = gender;
}

further you can also put condition for setting male/female on value= M/F

Answer 3

No need for custom serializer/deserializer if you can modify Gender class. For serialization you can use @JsonValue , for deserialization simple constructor (optionally annotated with @JsonCreator ):

public class Gender {
  @JsonCreator // optional
  public Gender(String desc) {
     // handle detection of "M" or "F"
  }

  @JsonValue
  public String asString() { // name doesn't matter
     if (...) return "M";
     return "F";
  }
}

Alternatively you could use a static factory method instead of constructor; if so, it must be annotated with @JsonCreator . And return type of method annotated with @JsonValue can be anything that Jackson knows how to serialize; here we use String, but Enum , POJO and such are fine as well.