Java boon JSON parser removing null values from output

Question

I have a small function which takes an input JSON string, parses it using boon into a Map, replaces a value for a particular key, returns back the JSON string of the modified Map.

The code is as follows:

// inputJson = {"key3":"A","key2":"B","key1":null,"keyX":[{"x":2019,"y":123,"z":456},{"x":2017,"y":234,"z":345},{"x":2018,"y":456,"z":567}]}

private static String sorter(String inputJson) {
    JsonParserAndMapper mapper = new JsonParserFactory().strict().create();

    Map<String, Object> map = mapper.parseMap(inputJson);

    List<?> l1 = (List<?>) map.get("keyX");

    sort(l1, Sort.sortBy("x"));

    map.replace("keyX", l1);

    for (String x: map.keySet())
        System.out.println(map.get(x));

    String outputJson = toJson(map);  // problem seems to be here

    return outputJson

// outputJson = {"key2":"B","key3":"A","keyX":[{"x":2017,"y":234,"z":345},{"x":2018,"y":456,"z":567},{"x":2019,"y":123,"z":456}]}

The problem is, when I do toJson(map) it removes the key with null values. So, if inputJson contains a key with a null value, it doesn't appear in the output. (Notice: key1 is missing in the output)

How can I parse this without losing the null fields?

Answer 1

Using toJson you are using a default serialiser factory. From boon source code:

public class JsonFactory {


    private static ObjectMapper json = JsonFactory.create();

    public static ObjectMapper create () {
        JsonParserFactory jsonParserFactory = new JsonParserFactory();
        jsonParserFactory.lax();

        return new ObjectMapperImpl(jsonParserFactory,  new JsonSerializerFactory());
    }
....
)

Instead of using toJson try using a serialiser factory with includeNulls()

JsonSerializer factory = new JsonSerializerFactory().includeNulls().create();