杰克逊特定字段名称

Question

I have this class:

@Data
public class DiscountDto {

    @JsonProperty(required = true)
    private DiscountType type;

    @JsonProperty(required = true)
    private double discountValue;
}

DiscountType is enum:

public enum  DiscountType {

    PERCENT, AMOUNT
}

I want to serialize the discountValue to a specific value, depending on the Enum value. If enum have value PERCENT , then discountValue must be serialize to percent_off . If enum have value AMOUNT then discountValue must be serialize to amount_off . How could I possibly do that?

Expected result:

If type == AMOUNT, I want discountValue name = amount_off

"discountDto": {
    "amount_off": "11.0",
    "type": "AMOUNT"
}

If type == PERCENT, I want discountValue name = percent_off

"discountDto": {
    "percent_off": "11.0",
    "type": "PERCENT"
}

Answer 1

Possible solutions:

1.Create a constructor with both DiscountType and discountValue and set directly the value of the percentOff or amountOff field:

@JsonInclude(Include.NON_NULL)
public class DiscountDto {

     private DiscountType type;

     @JsonProperty("percent_off")
     private Double percentOff;

     @JsonProperty("amount_off")
     private Double amountOff;

     public DiscountDto(DiscountType type, double discountValue){
          this.type = type;
          if(type.equals(DiscountType.PERCENT)){
              this.percentOff = discountValue;
          }else {
              this.discountOff = discountValue;
          }

     }
     //getters and setters
}

2.Use a custom JSON serializer:

public class DiscountDtoSerializer extends StdSerializer<DiscountDto> {

    public DiscountDtoSerializer() {
        this(null);
    }

    public DiscountDtoSerializer(Class<DiscountDto> t) {
        super(t);
    }

    @Override
    public void serialize(DiscountDto value, JsonGenerator jgen, SerializerProvider provider)
      throws IOException, JsonProcessingException {

        jgen.writeStartObject();
        jgen.writeNumberField("type", value.getDiscountType());
        if(value.getDiscountType().equals(DiscountType.PERCENT)){
            jgen.writeStringField("percent_off", value.getDiscountValue());
        }else{
            jgen.writeStringField("amount_off", value.getDiscountValue());
        }
        jgen.writeEndObject();
    }
 }

and your ObjectMapper should have this new serializer:

 ObjectMapper mapper = new ObjectMapper();
 SimpleModule module = new SimpleModule();
 module.addSerializer(DiscountDto.class, new DiscountDtoSerializer());
 mapper.registerModule(module);

Answer 2

This is a typical example of how not to do polymorphism. Don't get me wrong, I am not crticizing you, this has happend to most of us. This is a sort of inner-state polymorphism, that is, depending on the value of some property ( type even the name says it, right?) some other property gets a different meaning.

To solve the problem correctly, you should move the poperty type , at the level of the class, having a class for each type. You can start by having an abstract, uninstantiable type, and your specific types will derive from it.

You can find some sample implementation here , for technical reference.