oracle分页查询语句，java得到分页查询语句的方法

oracle分页查询语句
Sql代码 
select * from ( select a.*, rownum rn from (select * from table_name) a where rownum <= 40 ) where rn >= 21 

java得到分页查询语句的方法
Java代码 
/**
* 得到分页查询的语句
* @param queryString
* @param pageIndex
* @param pageSize
* @return
*/ 
public String getPageQl(String queryString, int pageIndex, int pageSize){ 
    //select * from ( select a.*, rownum rn from (select * from table_name) a where rownum <= 40 ) where rn >= 21 
    String ql = "select * from ( select page_.*, rownum rn from ("+queryString+") page_ where rownum <= "+pageIndex*pageSize+" ) where rn > "+(pageIndex-1)*pageSize; 
    //log.info(ql); 
    return ql; 
} 

排序的时候，最好再加上按id排序，解决翻页数据重复的问题。