List -> Map Tools, list into map

Providing two methods into the Map List, first convertOne conventional conversion, as a key in key map to a list of E value; a second key map key places to list a value 


@ the SuppressWarnings ( "an unchecked" )
 Final  public  class MapConverter { 

    Private  static  Final String the GET = "GET" ; 

    Private MapConverter () {
         the throw  new new AssertionError with ( "Util prohibiting reflection instantiated" ); 
    } 


    public  static <K, E> the Map <K , E> convertOne (List <E> List, String Key) {
         IF (CollectionUtils.isEmpty (List)) {
             return  null ; 
        } 

        the Map <K, E>map = null;
        try {
            Method getM = getMethod(list.get(0).getClass(), key);
            map = new HashMap<>();
            for (E en : list) {
                K k = (K) getM.invoke(en);
                map.put(k, en);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return map;
    }


    public static <K, E> Map<K, List<E>> convertList(List<E> list, String key) {
        if (CollectionUtils.isEmpty(list)) {
            return null;
        }
        Map<K, List<E>> map = null;
        try {
            Method getM = getMethod(list.get(0).getClass(), key);
            map = new HashMap<>();
            for (E en : list) {
                K k = (K) getM.invoke(en);
                List<E> res = map.get(k);
                if (res != null) {
                    res.add(en);
                } else {
                    List<E> l1 = new ArrayList<>();
                    l1.add(en);
                    map.put(k, l1);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return map;
    }


    private static Method getMethod(Class clazz, String key) throws NoSuchMethodException {
        if (key.startsWith(GET)) {
            return clazz.getMethod(key);
        }
        if (Character.isUpperCase(key.charAt(0))) {
            clazz.getMethod(GET + key);
        }
        return clazz.getMethod(GET + Character.toUpperCase(key.charAt(0)) + key.substring(1));
    }
}