gson.fromJson + JsonBooleanDeserializer + allFieldsNotNull()

AttributesExample.java

public class AttributesExample {

    private String str;
    private Double dbl;
    private Boolean bool;

    public boolean allFieldsNotNull() {
        return str != null && dbl != null && bool != null;
    }
}

Main.java

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;


public class Main {

    public static void main(String[] args) {
        GsonBuilder builder = new GsonBuilder();
        builder.registerTypeAdapter(Boolean.class, new JsonBooleanDeserializer());
        Gson gson = builder.create();
        String json;

        // TEST 1

        json = "{" +
                "\"str\": \"hi\", " +
                "\"dbl\": 2.0, " +
                "\"bool\": true" +
                "}";
        AttributesExample test1 = gson.fromJson(json, AttributesExample.class);
        System.out.println(test1.allFieldsNotNull()); // --> TRUE

        // TEST 2

        json = "{" +
                "\"str\": hi, " + // string without " is ok
                "\"dbl\": 2., " + // ending on . is ok
                "\"bool\": \"true\"" + // true with " is ok
                "}";
        AttributesExample test2 = gson.fromJson(json, AttributesExample.class);
        System.out.println(test2.allFieldsNotNull()); // --> TRUE

        // TEST 3

        json = "{" +
                "\"str\": \"hi\", " +
                "\"dbl\": 2.a0, " +
                "\"bool\": true" +
                "}";
        AttributesExample test3 = gson.fromJson(json, AttributesExample.class);
        System.out.println(test3.allFieldsNotNull()); // --> NumberFormatException: For input string: "2.a0"

        // TEST 4

        json = "{" +
                "\"str\": \"hi\", " +
                "\"dbl\": 2.0, " +
                "\"bool\": tre" + // isn't recognized as true or false and is default-casted to false because of the JsonBooleanDeserializer
                "}";
        AttributesExample test4 = gson.fromJson(json, AttributesExample.class);
        System.out.println(test4.allFieldsNotNull()); // --> FALSE

        // TEST 5

        json = "{" +
                "\"str\": \"hi\", " +
                "\"bool\": false" +
                "}";
        AttributesExample test5 = gson.fromJson(json, AttributesExample.class);
        System.out.println(test5.allFieldsNotNull()); // --> FALSE, because not all fields were set even so the two fields were set correctly
    }
}