CollectionUtils

public final class CollectionUtils {
    private CollectionUtils() {
    }

    public static  boolean isNullOrEmpty(Collection collection) {
        return collection == null || collection.isEmpty();
    }

    public static  boolean isNullOrEmpty(T[] array) {
        return array == null || array.length == 0;
    }

    public static  boolean isNullOrEmpty(Map map) {
        return map == null || map.isEmpty();
    }

    public static  boolean contains(T[] array, T val) {
        for (T t : array) {
            if (val.equals(t)) {
                return true;
            }
        }
        return false;
    }

    public static  T head(List list) {
        return list.get(0);
    }

    public static  T end(List list) {
        return list.get(list.size() - 1);
    }

    public static  List map(List list, Function function) {
        return list.stream().map(function).collect(Collectors.toList());
    }

    public static  LinkedHashMap ofMap(List list, Function keyFunction) {
        LinkedHashMap result = Maps.newLinkedHashMap();
        for (V value : list) {
            result.put(keyFunction.apply(value), value);
        }
        return result;
    }

    public static  ListMultimap groupBy(List list, Function keyFunction) {
        ListMultimap result = ArrayListMultimap.create();
        for (V value : list) {
            result.put(keyFunction.apply(value), value);
        }
        return result;
    }
    
	/**
	 * 分割List
	 * 
	 * @param list
	 *            待分割的list
	 * @param pageSize
	 *            每段list的大小
	 * @return List<>
	 */
	public static  List> splitList(List list, int pageSize) {
		int listSize = list.size(); 
		int page = (listSize + (pageSize - 1)) / pageSize;// 页数
		List> listArray = new ArrayList>();// 创建list数组,用来保存分割后的list
		for (int i = 0; i < page; i++) { // 按照数组大小遍历
			List subList = new ArrayList(); // 数组每一位放入一个分割后的list
			for (int j = 0; j < listSize; j++) {// 遍历待分割的list
				int pageIndex = ((j + 1) + (pageSize - 1)) / pageSize;// 当前记录的页码(第几页)
				if (pageIndex == (i + 1)) {// 当前记录的页码等于要放入的页码时
					subList.add(list.get(j)); // 放入list中的元素到分割后的list(subList)
				}
				if ((j + 1) == ((j + 1) * pageSize)) {// 当放满一页时退出当前循环
					break;
				}
			}
			listArray.add(subList);// 将分割后的list放入对应的数组的位中
		}
		return listArray;
	}
	
	 /**
     * list转换成字符串
     **/
	public static String getStringFromIntegerList(List list) {
		String str=null;
		if(CollectionUtils.isNullOrEmpty(list)) {
			StringBuffer strBf = new StringBuffer();
			list.stream().forEach(m -> strBf.append(m).append(ConstUtils.CHAR_COMMA));
			str= strBf.toString().substring(0, strBf.length() - 1);
		}
		return str;
	}
	
	 /**
     * list转换成字符串
     **/
	public static String getStringFromStringList(List list) {
		String str=null;
		if(CollectionUtils.isNullOrEmpty(list)) {
			StringBuffer strBf = new StringBuffer();
			list.stream().forEach(m -> strBf.append(m).append(ConstUtils.CHAR_COMMA));
			str= strBf.toString().substring(0, strBf.length() - 1);
		}
		return str;
	}
	
	/**
	 * 返回a与b的交集的新List.
	 */
	public static  List intersection(Collection a, Collection b) {
		List list = new ArrayList();

		for (T element : a) {
			if (b.contains(element)) {
				list.add(element);
			}
		}
		return list;
	}
}