public static String selectAmount(String sql)//选取商品数量
    {
        String flag ="";
        try
        {   
            Context initial = new InitialContext();//初始化上下文  
            //其中mysql为数据源jndi名称         
            DataSource ds = (DataSource)initial.lookup("java:comp/env/jdbc/chaoshids");
            Connection con=ds.getConnection();//得到连接
            Statement st = con.createStatement();//声明语句
            ResultSet rs = st.executeQuery(sql); //执行语句得到结果集
            if(rs.next())
            {
                String flagq = rs.getString(1);
                flag = new String(flagq.getBytes("ISO-8859-1"),"gb2312");
            }            
            rs.close();//关闭结果集
            st.close();//关闭语句
            con.close();//归还连接
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
        return flag;
    }