code: private Comparator<String> getInitedAliasComparator() {
  		if (MapUtil.isEmpty(this.headerAlias)) {
  			return null;
  		}
  		Comparator<String> aliasComparator = this.aliasComparator;
  		if (null == aliasComparator) {
  			Set<String> keySet = this.headerAlias.keySet();
  			aliasComparator = new IndexedComparator<>(keySet.toArray(new String[keySet.size()]));
  			this.aliasComparator = aliasComparator;
  		}
  		return aliasComparator;
  	}
docs: 获取单例的别名比较器，比较器的顺序为别名加入的顺序
  
  @return Comparator
  @since 4.1.5