Convert JSON object to Java object with different format using GSON

I have a response that returns a json object in following format:


"playerId": "001",
"name": "michel",
"age": 21,
"nation": "USA",
"ratings": [

"type": "speed",
"score": "0121"
,

"type": "accuracy",
"score": "85"

],
"teaminfo":
"teamName": "HON",
"isValid": "true"




and I have a Java Class as :

public class MyRider
public String playerId;
public String name;
public int age;
public String speed;
public String accuracy;
public String teamName;
public String isValid;
//getter, setter...



I want to map the JSON object into Java object using GSON.

I tried using JsonDeserializationContext deserialize, and it returned null for the nested values in JSON.

JsonDeserializationContext

null

1 Answer
1

If you cannot change the JSON to return exactly what you want, I suggest you create classes to match it:

MyRider:

public class MyRider
private String playerId;
private String name;
private int age;
private String nation;
private List<Rating> ratings;
private TeamInfo teaminfo;

// getters, setters, toString override



Rating:

public class Rating
private String type;
private String score;

// getters, setters, toString override



TeamInfo:

private static class TeamInfo
private String teamName;
private String isValid;

// getters, setters, toString override



Then simply deserialize as normal:

MyRider rider = gson.fromJson(json, MyRider.class);


If you need exactly the fields you've specified in MyRider in your question, consider a transformer class to map the full class above to your needs.

It's also possible to do this with a custom deserializer, but slightly pointless as GSON provides the normal mapping for you which you can then adapt.

Here is an example with a deserializer:

public class MyRiderDeserializer implements JsonDeserializer<MyRider>

@Override
public MyRider deserialize(JsonElement json, Type typeOfT,
JsonDeserializationContext context)
throws JsonParseException
MyRider rider = new MyRider();
if(json.isJsonObject())
JsonObject riderObj = json.getAsJsonObject();

rider.setPlayerId(riderObj.get("playerId").getAsString());
rider.setName(riderObj.get("name").getAsString());
rider.setAge(riderObj.get("age").getAsInt());

JsonArray ratingsArray = riderObj.get("ratings").getAsJsonArray();
for(JsonElement ratingElem : ratingsArray)
JsonObject ratingObj = ratingElem.getAsJsonObject();
String type = ratingObj.get("type").getAsString();
switch(type)
case "speed":
rider.setSpeed(ratingObj.get("score").getAsString());
break;
case "accuracy":
rider.setAccuracy(ratingObj.get("score").getAsString());
break;
default:
break;



JsonObject teamInfo = riderObj.get("teaminfo").getAsJsonObject();
rider.setTeamName(teamInfo.get("teamName").getAsString());
rider.setIsValid(teamInfo.get("isValid").getAsString());


return rider;




Note this does not include any checks to validate whether the properties are actually there and is the simplest possible custom deserializer I could think of. To use it, you must register the type adapter at Gson creation time:

Gson

Gson gson = new GsonBuilder()
.registerTypeAdapter(MyRider.class, new MyRiderDeserializer())
.create();

MyRider myRider = gson.fromJson(reader, MyRider.class);


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