collection 转Map

    public static <E,K,V> Map<K,V> listToMap(Collection<E> collection, Function<? super E,? extends K> keyMapper,Function<? super E,? extends V> valueMapper){
        if(collection == null || collection.size() == 0){
            return null;
        }
        return collection.stream().collect(Collectors.toMap(keyMapper, valueMapper,(oldValue,newValue)->oldValue));
    }