Deserialize JSON using Jackson annotations with dynamic field

Question

I have a json response from a WebAPI in this format:

{
    "Status": "Successful Request",
    "ErrorCode": 200,
    "ResultCount": 1,
    "Trends": {
        "39381": {
            "user_distance_units": 1,
            "total_sep": 0,
            "max_power": 0,
            "max_rpm": 0,
            "max_heart_rate_bpm": 0,
            "distance": 0,
            "avg_power": 0,
            "avg_rpm": 0,
            "avg_hr": 0,
            "calories": 0,
            "classes": "0",
            "max_avg_power": 0,
            "max_avg_rpm": 0,
            "max_avg_hr": 0
        }
    }
}

I am trying to map it to a POJO. I am having some difficulty with this one using Jackson annotations. The 39381 is a client ID, for some reason the webservice supplies this with the response. That client ID is dynamic and will change with every call for a different user. I cant seem to use the Jackson annotation @JsonProperty in this instance. The mapping becomes more complex. Since i really do not need the Client ID information, I would really like to skip that and just map the data to this Trends class:

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({ "user_distance_units", "total_sep", "max_power", "max_rpm", "max_heart_rate_bpm", "distance",
        "avg_power", "avg_rpm", "avg_hr", "calories", "classes", "max_avg_power", "max_avg_rpm", "max_avg_hr" })
public class Trends
{

    @JsonProperty("user_distance_units")
    private Integer userDistanceUnits;
    @JsonProperty("total_sep")
    private Integer totalSep;
    @JsonProperty("max_power")
    private Integer maxPower;
    @JsonProperty("max_rpm")
    private Integer maxRPM;
    @JsonProperty("max_heart_rate_bpm")
    private Integer maxHeartRateBPM;
    @JsonProperty("distance")
    private Integer distance;
    @JsonProperty("avg_power")
    private Integer avgPower;
    @JsonProperty("avg_rpm")
    private Integer avgRPM;
    @JsonProperty("avg_hr")
    private Integer avgHr;
    @JsonProperty("calories")
    private Integer calories;
    @JsonProperty("classes")
    private Integer classes;
    @JsonProperty("max_avg_power")
    private Integer maxAvgPower;
    @JsonProperty("max_avg_rpm")
    private Integer maxAvgRPM;
    @JsonProperty("max_avg_hr")
    private Integer maxAvgHr;
    @JsonIgnore
    private Map<String, Object> additionalProperties = new HashMap<String, Object>();

Is there a way to do this?

Answer 1

The trends are returned as a map keyed on ClientId. So you may define a top level Response object with inner map of trends:

   class Response {
    @JsonProperty("Status")
    private String status;
    @JsonProperty("ErrorCode")
    private  int errorCode;
    @JsonProperty("ResultCount")
    private  int resultCount;
    @JsonProperty("Trends")
    private Map<String, Trends> trends;
   }

If you do not care about the the clientId you may add a getter that simply attempts to return the first element of the map.