GSON converting Integer value to Boolean value dynamically for specific fields

Beyazid :

How can I handle getting a field same name but different types? I'm getting sometimes integer value sometimes boolean value from API in the same request. I wonder how to handle when I get Json like these. I created type adapter but it doesn't work

I thought about creating different POJO classes. But this problem is not for just one request. I don't prefer to create POJOs for this reason. Btw I saw similar questions but it doesn't fix my problem.

{
  "name" : "john doe",
  "isValid" : true 
}

sometime I get int

{
  "name" : "john doe",
  "isValid" : 1 
}

I am getting unexpected json exception when getting an integer

class XModel{
    private boolean isValid;
    ...
    ...
}

I want to return a boolean value for every request. Does anyone know how to solve this problem?

Edit : I want to prevent instanceOf keyword via Type Adapter

---

Solution: @Michał Ziober's respond works for me.

class BooleanJsonDeserializer implements JsonDeserializer<Boolean> {

    private final Set<String> TRUE_STRINGS = new HashSet<>(Arrays.asList("true", "1", "yes"));

    @Override
    public Boolean deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        System.out.println(json);
        JsonPrimitive jsonPrimitive = json.getAsJsonPrimitive();
        if (jsonPrimitive.isBoolean()) {
            return jsonPrimitive.getAsBoolean();
        } else if (jsonPrimitive.isNumber()) {
            return jsonPrimitive.getAsNumber().intValue() == 1;
        } else if (jsonPrimitive.isString()) {
            return TRUE_STRINGS.contains(jsonPrimitive.getAsString().toLowerCase());
        }

        return false;
    }
}

Michał Ziober :

If XModel class is not big you can write your custom deserialiser as below where you have control over incoming element:

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;

import java.io.File;
import java.io.FileReader;
import java.lang.reflect.Type;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

public class GsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        Gson gson = new GsonBuilder()
                .registerTypeAdapter(XModel.class, new XModelJsonDeserializer())
                .create();

        System.out.println(gson.fromJson(new FileReader(jsonFile), XModel.class));
    }
}

class XModelJsonDeserializer implements JsonDeserializer<XModel> {

    private final Set<String> TRUE_STRINGS = new HashSet<>(Arrays.asList("true", "1", "yes"));

    @Override
    public XModel deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        XModel response = new XModel();
        JsonObject jsonResponse = (JsonObject) json;
        response.setName(jsonResponse.get("name").getAsString());
        // other fields

        JsonElement dataElement = jsonResponse.get("isValid");
        if (dataElement.isJsonNull()) {
            response.setValid(false);
        } else if (dataElement.isJsonPrimitive()) {
            JsonPrimitive jsonPrimitive = dataElement.getAsJsonPrimitive();
            if (jsonPrimitive.isBoolean()) {
                response.setValid(jsonPrimitive.getAsBoolean());
            } else if (jsonPrimitive.isNumber()) {
                response.setValid(jsonPrimitive.getAsNumber().intValue() == 1);
            } else if (jsonPrimitive.isString()) {
                response.setValid(TRUE_STRINGS.contains(jsonPrimitive.getAsString()));
            }
            System.out.println("Json data is primitive: " + dataElement.getAsString());
        } else if (dataElement.isJsonObject() || dataElement.isJsonArray()) {
            response.setValid(true); //?!?!
        }

        return response;
    }
}

For below JSON payload:

{
  "name" : "john doe",
  "isValid" : true
}

above program prints:

Json data is primitive: true
XModel{name='john doe', isValid=true}

For JSON payload:

{
  "name" : "john doe",
  "isValid" : 1
}

prints:

Json data is primitive: 1
XModel{name='john doe', isValid=true}

Your model is clear because all work is done on deserialiser level.

A little bit much precise solution would be to serialise primitive only. Let's assume that model looks like below:

class XModel {

    private String name;

    @JsonAdapter(value = BooleanJsonDeserializer.class)
    private boolean isValid;

    // getters, setters
}

and our BooleanJsonDeserializer deserialiser looks like below:

class BooleanJsonDeserializer implements JsonDeserializer<Boolean> {

    private final Set<String> TRUE_STRINGS = new HashSet<>(Arrays.asList("true", "1", "yes"));

    @Override
    public Boolean deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        System.out.println(json);
        JsonPrimitive jsonPrimitive = json.getAsJsonPrimitive();
        if (jsonPrimitive.isBoolean()) {
            return jsonPrimitive.getAsBoolean();
        } else if (jsonPrimitive.isNumber()) {
            return jsonPrimitive.getAsNumber().intValue() == 1;
        } else if (jsonPrimitive.isString()) {
            return TRUE_STRINGS.contains(jsonPrimitive.getAsString().toLowerCase());
        }

        return false;
    }
}

You need to only annotate every boolean property with this adapter in your model and it is ready to handle: 1, True, etc.