jdbc 可滚动结果集合，分页技术

jdbc2.0
一.可滚动的结果集

String sql = "select * from emp";

Connection conn = DriverManager.getConnetion(url, username, password);

Statement stmt = conn.createStatement(

ResultSet.TYPE_SCROLL_INSENSITIVE,

ResultSet.CONCUR_READ_ONLY

);

ResultSet rs = stmt.executeQuery(sql);

rs.first();

rs.last();

rs.beforeFirst();

rs.previous();

rs.next();

rs.absolute(n);

rs.relative(n);

//结果集已耗尽 (用尽的结果集)



思考:

在线考试系统,99道题,随机抽取20道题.重复题号的问题.

1)获得20个随机数

2)rs.absolute(n)跳到指定的记录



Collection                 Map

  |       |                  |

Set       List             Hashtable

|       |         |         |

HashSet ArrayList Vector   Properties



二.分页技术

m-n条记录的获取方式:[m, n)

select id, user_id, login_time,logout_time

from(

select id, user_id, login_time, logout_time, rownum rn

from mytemp where rownum < 20 )

where rn >= 10;



--mysql

select * from mytemp

limit 10, 10;





分页问题的需求:

已知条件:每页pageSize条,第n页

求:第n页的记录.

每页10条.pageSize = 10;

1: 1-10

2: 11-20

...

5: 41-50

...

n: from: (n-1)* pageSize + 1

   to : from + pageSize

   [from, to)



totalNumber // 总的记录数

totalPage //总的页数



if (totalNumber % pageSize == 0)

totalPage = totalNumber/pageSize;

else{

totalPage = totalNumber/pageSize+1;

}



totalPage =



if (page > totalPage)

page = totalPage;

else if (page <= 0 )

page = 1;





三.数据类型:大对象: Blob / Clob

create table stu_ning(

id number primary key,

name varchar2(20),

photo blob

);

create sequence stu_ning_seq;



如果文件存放于项目的根目录下

File f = new File("mykfc.jpg");

如果文件存放于项目的src目录下

File f = new File("src\\mykfc.jpg");

如果文件存放于项目的src目录的包下

File f = new File("src\\com\\xxxx\\mykfc.jpg");