public Map<String,String> A() {
  Map<String,String> map = new HashMap<>();
  map = MapUtil.toCamelCaseMap(map);
  return map;
}

public Map<String,String> B() {
  // 假如 newMap里有值 {name:"a",age:"2"}
  Map<String,String> newMap = A();
  // 需求是获取只有name的map,但此时 newMap 为空。
  newMap = MapUtil.filter(newMap,"name");
}

public class MapWrapper<K, V> implements Map<K, V>, Iterable<Map.Entry<K, V>>, Serializable, Cloneable {
	private static final long serialVersionUID = -7524578042008586382L;

}

public static <K, V> Map<K, V> filter(Map<K, V> map, K... keys) {
        final Map<K, V> map2 = ObjectUtil.clone(map);
        if (isEmpty(map2)) {
            return map2;
        }

        map2.clear();
        for (K key : keys) {
            if(map.containsKey(key)) {
                map2.put(key, map.get(key));
            }
        }
        return map2;
    }