Question

Hello I had this follow json code.

[{"check":{"domain":"qwe.coedu.br"}},{"check":{"domain":"qwe.com.br"}},{"check":{"domain":"qwe.com"}}]"

How do to convert this json in my object

class Check {String domain , String status ...}

It return a List<Check>, but the Check attributes are null. See my code. with Gson.

Gson gson = new Gson();
    Type fooType = new TypeToken<Collection<Check>>(){}.getType();
    System.out.println(((List<Check>)gson.fromJson("[{\"check\":{\"status\":\"2\",\"domain\":\"william.com.br\"}}]", fooType)).get(0).getDomain());

When I debug my returned list, this contains all objects in list, but all with your attributes null.

What is wrong ?

Answer 1

You need a customized converter, because you have a list of objects that holds a property named check. And this property is of a class that has the properties domain and status.

Two possibilities here:

1. if you don’t want to change the Json format, or you simply can’t probably write your own JsonDeserializer, in which you will instanciate your Check object and then set the properties by your own is the best choice;
2. or you could modify your check class in order to hold a check property of a type that holds a property named domain and another one status.

For the second case is pretty clear what needs to be done, but for the first case you could do something like:

import java.lang.reflect.Type;
import java.util.Collection;

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.reflect.TypeToken;

public class GsonTestClass {

    static class MyDeserializer implements JsonDeserializer<Check> {

        public Check deserialize(JsonElement arg0, Type arg1,
                JsonDeserializationContext arg2) throws JsonParseException {
            JsonObject jsonObject = arg0.getAsJsonObject().get("check").getAsJsonObject();
            // this code could be improved with null checks and so on...
            return new Check( //
                    jsonObject.get("domain").getAsString(), //
                    jsonObject.get("status").getAsString() //
            );
        }

    }

    public static void main(String args[]) {
        Gson gson = new GsonBuilder().registerTypeAdapter(Check.class, new MyDeserializer()).create();
        String json = "[{\"check\":{\"status\":\"2\",\"domain\":\"william.com.br\"}}]";
        Type fooType = new TypeToken<Collection<Check>>() {}.getType();
        System.out.println((gson.fromJson(json, fooType)));
    }

    static class Check {

        private String domain;
        private String status;

        public Check() {
        }

        public Check(String domain, String status) {
            super();
            this.domain = domain;
            this.status = status;
        }

        public String getDomain() {
            return domain;
        }

        public void setDomain(String domain) {
            this.domain = domain;
        }

        public String getStatus() {
            return status;
        }

        public void setStatus(String status) {
            this.status = status;
        }

        @Override
        public String toString() {
            return "Check: " + domain + " - " + status;
        }

    }

}