如何绑定JSON Object到POJO

Question

I am consuming an API whose structure is as below.

{
"icao": "VIDP",
"iata": "DEL",
"name": "Indira Gandhi International Airport",
"location": "New Delhi",
"country": "India",
"country_code": "IN",
"longitude": "77.103088",
"latitude": "28.566500",
"link": "/world-airports/VIDP-DEL/",
"status": 200
}

My POJO is as below.

package com.myapp.flightreservation.model;

import com.fasterxml.jackson.annotation.JsonProperty;

import lombok.Data;

@Data
public class AirportInfo {
    @JsonProperty("countryCode")
    private String country_code;

}

When I run my application I get the below.

{
"countryCode": null
}

If I change my POJO to below, I get the output.

package com.myapp.flightreservation.model;

import com.fasterxml.jackson.annotation.JsonProperty;

import lombok.Data;

@Data
public class AirportInfo {
    @JsonProperty("country_code")
    private String country_code;
}

OUTPUT:

{
"country_code": "IN"
}

I want to follow the camel case in my API response. As per my knowledge, if I use @JsonProperty("countryCode"), country_code should be mapped to countryCode.

Answer 1

Yes Correct. You can achieve that by using @JsonProperty("countryCode")

Answer 2

If you want to consume JSON with a field called country_code (AirportInfoIn) and emit JSON with the same element called countryCode (AirportInfoOut) then you need to define 2 different POJOs. Otherwise you will trip up on the way in or out - as you have seen.

You can save some coding by using inheritance as follows:

@Data
public class AirportInfo implements Serializable {
    
    private String icao;
    private String iata;
    private String name;
    private String location;
    private String country;
    private String longitude;
    private String latitude;
    private String link;
    private Integer status;

}

@Data
public class AirportInfoIn extends AirportInfo {

    private String country_code;

}

@Data
public class AirportInfoOut extends AirportInfo {

// to make an AirportInfoOut from an AirportInfoIn
public AirportInfoOut(AirportInfoIn airportInfoIn) {
    this.countryCode = airportInfoIn.getCountry_code();
    this.icao = airportInfoIn.getIcao();
    // etc
}

private String countryCode;
    
}

Note: the @JsonProperty is redundant if the Java fieldname matches the JSON