code: public static <T> Set<T> randomEleSet(Collection<T> collection, int count) {
  		ArrayList<T> source = new ArrayList<>(new HashSet<>(collection));
  		if (count > source.size()) {
  			throw new IllegalArgumentException("Count is larger than collection distinct size !");
  		}
  
  		final HashSet<T> result = new HashSet<T>(count);
  		int limit = collection.size();
  		while (result.size() < count) {
  			result.add(randomEle(source, limit));
  		}
  
  		return result;
  	}
docs: 随机获得列表中的一定量的不重复元素，返回Set
  
  @param <T> 元素类型
  @param collection 列表
  @param count 随机取出的个数
  @return 随机元素
  @throws IllegalArgumentException 需要的长度大于给定集合非重复总数