JavaでJSON文字列をHashMapに変換するにはどうすればよいですか?

public static Map<String, Object> jsonToMap(JSONObject json) throws JSONException {
    Map<String, Object> retMap = new HashMap<>();

    if (json != JSONObject.NULL) {
        retMap = toMap(json);
    }
    return retMap;
}

public static Map<String, Object> toMap(JSONObject object) throws JSONException {
    Map<String, Object> map = new HashMap<>();

    Iterator<String> keysItr = object.keys();
    while (keysItr.hasNext()) {
        String key = keysItr.next();
        Object value = object.get(key);

        if (value instanceof JSONArray) {
            value = toList((JSONArray) value);
        } else if (value instanceof JSONObject) {
            value = toMap((JSONObject) value);
        }
        map.put(key, value);
    }
    return map;
}

public static List<Object> toList(JSONArray array) throws JSONException {
    List<Object> list = new ArrayList<>();
    for (int i = 0; i < array.length(); i++) {
        Object value = array.get(i);
        if (value instanceof JSONArray) {
            value = toList((JSONArray) value);
        } else if (value instanceof JSONObject) {
            value = toMap((JSONObject) value);
        }
        list.add(value);
    }
    return list;
}

import com.fasterxml.jackson.databind.ObjectMapper;

Map<String, Object> mapping = new ObjectMapper().readValue(jsonStr, HashMap.class);