将json串如下:
{
"1":[{"id":001,"age":20,"type":2,"code":"101","password":123456}, {"id":002,"age":22,"type":1,"code":"102","password":123456}],
"2":[{"id":003,"age":23,"type":1,"code":"103","password":123456}]
}
转换为:Map<String, List<User>> 类型 

1.  思路就是，json字符串其实总得来说就是一个key-value的形式，应该是满足了最终想要的Map<String, List<Unit>>的结构了，所以直接一个Collectors.toMap就搞定啦

Map<String, List<User>> result = JSONObject.parseObject(s)
                                           .entrySet().stream()
                                           .collect(Collectors.toMap(Map.Entry::getKey, entry -> JSONObject.parseArray(String.valueOf(entry.getValue()), User.class)));

2. 自己封装一个将 json 解析为常用数据类型的工具类

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

    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<String, Object>();

    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<Object>();
    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;
}