Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
       RowSet rowSet = new JdbcRowSetImpl();
       
       
       rowSet.setUrl("jdbc:sqlserver://localhost:1433;DatabaseName=TaxiManager");         
       rowSet.setUsername("sa");
       rowSet.setPassword("li");   
       
       
       rowSet.setCommand("select user_names from users");           
       System.out.println("连接建立");
       
       rowSet.execute();
       System.out.println("命令执行了");当执行到 rowSet.execute()时会抛出空指针异常,求解!!!在线等!!