How to convert hashmap to JSON object in Java

Question

How to convert or cast hashmap to JSON object in Java, and again convert JSON object to JSON string?

Answer 1

No need for Gson or JSON parsing libraries. Just using new JSONObject(Map).toString(), e.g:

/**
 * convert target map to JSON string
 *
 * @param map the target map
 * @return JSON string of the map
 */
@NonNull public String toJson(@NonNull Map map) {
    final Map flatMap = new HashMap<>();
    for (String key : map.keySet()) {
        try {
            flatMap.put(key, toJsonObject(map.get(key)));
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }
    try {
        // 2 indentSpaces for pretty printing
        return new JSONObject(flatMap).toString(2);
    } catch (JSONException e) {
        e.printStackTrace();
        return "{}";
    }
}