问在Java中扁平化从json字符串派生的hashmap

EN

{"MainForm":{"OriginMerd":{"id":"onMggagerd","number":5,"tests":{"Blod":{"blodid":"1","glucose":52}}}}}

    Stream<Map.Entry<String, String>> flatten(Map<String, Object> map) 
    {
        return map.entrySet()
                .stream()
                .flatMap(this::extractValue);
    }

    Stream<Map.Entry<String, String>> extractValue(Map.Entry<String, Object> entry) {
        if (entry.getValue() instanceof String) {
            return Stream.of(new AbstractMap.SimpleEntry(entry.getKey(), (String) entry.getValue()));
        } else if (entry.getValue() instanceof Map) {
            return flatten((Map<String, Object>) entry.getValue());
        }
        return null;
    }

    @ReactMethod
    public void testFunc(String jsonString, Callback cb){
        Map<String,Object> map = new HashMap<>();

        ObjectMapper mapper = new ObjectMapper();

        try {
            //convert JSON string to Map
            map = mapper.readValue(String.valueOf(jsonString), new TypeReference<Map<String, Object>>() {
            });


            Map<String, String> flattenedMap = flatten(map)
                     .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

            for (Map.Entry<String, String> entry : flattenedMap.entrySet()) {
                Log.e("flatmap",entry.getKey() + "/" + entry.getValue());

                //System.out.println(entry.getKey() + "/" + entry.getValue());
            }
        } catch (JsonParseException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        Log.e("JSONSTRING", jsonString);

        cb.invoke("OK");
    }