MAP排序

//我们了解treemap是可以排序的，我们可以自己更改排序的手段。
Map<String,String> bankGroup = new TreeMap<String,String>(
    new  Comparator() {
      private RuleBasedCollator collator =null;
      {
        collator = (RuleBasedCollator)Collator.getInstance(java.util.Locale.CHINA);//因为key中可能含有中文
      }
            public int compare(Object o1, Object o2) {
                 //如果有空值，直接返回0
                if (o1 == null || o2 == null) return 0; 
                CollationKey ck1 = collator.getCollationKey(String.valueOf(o1));
                CollationKey ck2 = collator.getCollationKey(String.valueOf(o2));
                return ck1.compareTo(ck2);              
          }
        }
   );