数据库连接池

计算确定数据表一共分几页：101/pageSize=100/10=10页。rows = select count(1) from users;方法１：pageCount = rows/pageSize (rows%pageSize==0?0:1); 方法２：pageCount = (rows (pageSize-1))/(pageSize);public void doGet(HttpServletRequest req,

<span>计算确定数据表一共分几页：
	101/pageSize=100/10=10页。
	rows = select count(1) from users;
	方法１：pageCount = rows/pageSize + (rows%pageSize==0?0:1);
　　方法２：pageCount = (rows+ (pageSize-1))/(pageSize);
public void doGet(HttpServletRequest req, HttpServletResponse response)
			throws ServletException, IOException {
		//第一步：定义每页显示多少行
		int pageSize = 10;
		try{
			//第二步：获取数据表中有多少行
			QueryRunner run = new QueryRunner(DataSourceUtils.getDatasSource());
			String sql = "select count(*) from users";
			Object o = run.query(sql,new ScalarHandler());
			int rows = Integer.parseInt(o.toString());
			//第三步：计算一共分多少页
			int pageCount= rows/pageSize+(rows%pageSize==0?0:1);
			//将页数放到req
			req.setAttribute("pageCount",pageCount);
			
		}catch(Exception e){
			e.printStackTrace();
		}
		//转发到
		req.getRequestDispatcher("/jsps/show.jsp").forward(req, response);
		
	}
</span>

第四步：分析limit的开始位置

用户请求的面码	start	算法：
1	Limit 0,pageSize	Start = (currentPage-1)*pageSize
2	Limit 10,pageSize
3	Limit 20,pageSize

用户请求的面码

start

算法：

1

Limit 0,pageSize

Start

= (currentPage-1)*pageSize

2

Limit 10,pageSize

当前页码	页码范围	算法
1	1~10	If(currentPage<=pageNum/2)   1~10
2
3
4
5
6	2~11	6-4=2 = 6-(pageNum/2-1)=2 = startNo endNo = startNo+(pageNum-1)=11
7	3~12
8	4~13
9
10
11		11-4 = 7 endNo = 7+9=16 endNo = 11; startNo = 2 = endNo-(pageNum-1);

3

Limit 20,pageSize

  第五步：对分页以后页码再分页

       每个页面，最多显示10个页码        pageNum=10;

startNo endNo

 

当前页码	页码范围	算法
1	1~10	If(currentPage<=pageNum/2)   1~10
2
3
4
5
6	2~11	6-4=2 = 6-(pageNum/2-1)=2 = startNo endNo = startNo+(pageNum-1)=11
7	3~12
8	4~13
9
10
11		11-4 = 7 endNo = 7+9=16 endNo = 11; startNo = 2 = endNo-(pageNum-1);