总行数(num): select count(1) from stud;
每页显示的行数(n): 固定值---已知的一个常量
页数: pageSize= num/n +( (num%n==0)?0:1 )
当前页号: currentPage
当前要显示的页面数据的起始行号和终止行号
startN: (currentPage-1)*pageSize
如何显示从startN开始的pageSize条记录
select * from stud limit startN, pageSize;
增加了：
开始的页码：
showStart
结束的页码：
showEnd

package cn.hncu.dao;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.MapListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;
import cn.hncu.domain.Person;
import cn.hncu.pubs.C3p0Pool;
public class PageJdbc implements IPageDAO {
    private final int pageSize = 10;// 每页显示的行数
    @Override
    public Map<String, Object> query(Integer pageNo, Person person)
            throws NumberFormatException, SQLException {
        Map<String, Object> result = new HashMap<String, Object>();
        // 获取总页数 pageCount = rows/pageSize + ( (rows%pageSize==0)?0:1 )
        // 总行数rows
        String sql = "select count(1) from person where 1=1 ";// 用来查总行数
        String sql2 = "select * from person where 1=1 ";// 用来查表内容
        if (person.getId() != null && person.getId().trim().length() != 0) {
            sql = sql + "and id like '%" + person.getId() + "%'";
            sql2 = sql2 + "and id like '%" + person.getId() + "%'";
        }
        if (person.getName() != null && person.getName().trim().length() != 0) {
            sql = sql + "and name like '%" + person.getName() + "%'";
            sql2 = sql2 + "and name like '%" + person.getName() + "%'";
        }
        //System.out.println(sql2);
        QueryRunner run = new QueryRunner(C3p0Pool.getDataSource());
        int rows = Integer.parseInt("" + run.query(sql, new ScalarHandler()));
        // 总页数
        int pageCount = rows / pageSize + ((rows % pageSize == 0) ? 0 : 1);
        result.put("pageCount", pageCount);// 封装到result
        // 分页页面内容datas
        // 起始行号
        int startN = (pageNo - 1) * pageSize;
        sql2 = sql2+ " limit "+startN+", "+pageSize;
        List<Map<String, Object>> datas = run.query(sql2, new MapListHandler());
        result.put("datas", datas);//封装到result
        return result;
    }
}

package cn.hncu.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.SQLException;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import cn.hncu.domain.Person;
import cn.hncu.service.IPageService;
import cn.hncu.service.PageServiceImpl;
public class PageServlet extends HttpServlet {
    //注入servlet
    IPageService service = new PageServiceImpl();
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        String pageNo = request.getParameter("page");
        if(pageNo==null || pageNo.trim().length()==0){
            pageNo = "1";
        }
        Integer iPageNo =1;
        try {
            iPageNo = Integer.parseInt(pageNo);
        } catch (NumberFormatException e) {
            request.getRequestDispatcher(request.getContextPath()+"/index.jsp").forward(request, response);
        }
        Person person =null;
        //区分是Post还是GET方式请求，前者是新的查询，后者是原查询结果中进行翻页
        if(request.getMethod().equalsIgnoreCase("get")){//翻页
            //从session中把旧的查询条件值对象取出来
            person = (Person) request.getSession().getAttribute("person");
            if(person==null){//没有进行第一次查询之前，person就是需要我们new出来一个空的
                person = new Person();
            }
        }else{//POST方式---新的查询
            //收集模糊查询的输入参数
            String id = request.getParameter("id");
            String name = request.getParameter("name");
            person = new Person();
            person.setId(id);
            person.setName(name);
            //放入session,这样下一次翻页才能读取出来
            request.getSession().setAttribute("person", person);
        }
        try {
            Map<String, Object> result = service.query(iPageNo, person);
            //给结果集补一个数据:currentPage --当前页号
            result.put("currentPage", iPageNo);
            //把结果集放入容器中
            request.setAttribute("result", result);
            //分页后的分页--向前端多传送两个数据(起始和末尾页号)：showStart和showEnd
            int showSize=10;//每页显示几行
            int showStart=0;//从第几个页号开始显示
            int showEnd=0;//显示到第几个页号
            //pageCount---总页数
            //如果所有页码不足showSize:  showStart=1,showEnd=pageCount
            int pageCount = Integer.parseInt(""+result.get("pageCount"));
            if(pageCount<=showSize){//不需要二次分页
                showStart=1;
                showEnd=pageCount;
            }else{//需要二次分页
                //如果当前页号iPageNo<=showSize/2时，showStart=1
                if(iPageNo<=showSize/2){
                    showStart=1;
                    showEnd=showSize;
                }else{
                    showStart = iPageNo - showSize/2;
                    showEnd = showStart + showSize-1;
                }
                if(showEnd>pageCount){
                    showEnd=pageCount;
                    showStart = showEnd-showSize-1;
                }
            }
            //存储showStart和showEnd
            request.setAttribute("showStart", showStart);
            request.setAttribute("showEnd", showEnd);
            //转到结果页面
            request.getRequestDispatcher("/jsps/show.jsp").forward(request, response);
        } catch (NumberFormatException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>演示数据分页</title>
    <link rel="stylesheet" href="<c:url value='/css/table.css' />" />
    <script type="text/javascript">
        function sub(obj){
            window.location.href="<c:url value='/PageServlet?page=' />"+obj.value;
        }
    </script>
  </head>
  <body>
     <h3>数据查询</h3>
     <form action="<c:url value='/PageServlet'/>" method="post">
            ID:<input type="text" name="id" value="${person.id }"> &nbsp;
            姓名:<input type="text" name="name" value="${person.name }" > &nbsp;&nbsp;
            <input type="submit" value="模糊查询">
     </form>
    <h3>当前页的内容:</h3>
    <table>
        <tr><th>学号</th><th>姓名</th><th>地址</th><th>年龄</th></tr>
        <c:forEach items="${result.datas}" var="map">
            <tr>
                <td>${map.id}</td>
                <td>${map.name}</td>
                <td>${map.address}</td>
                <td>${map.age}</td>
            </tr>
        </c:forEach>
    </table>
    <c:if test="${result.currentPage!=1}">
        <span class="pc">
            <a href='<c:url value="/PageServlet?page=${result.currentPage-1}"></c:url>'>上一页</a>
        </span>
    </c:if>
    &nbsp;&nbsp;
    <c:forEach begin="${showStart}" end="${showEnd}" var="idx">
        <c:if test="${idx==result.currentPage}" var="isNow">
            <span class=now>${idx}</span>
        </c:if>         
        <c:if test="${!isNow }">
            <span class="pc">
                <a href='<c:url value="/PageServlet?page=${idx}"></c:url>'>${idx}</a>
            </span>
        </c:if>
        &nbsp;&nbsp;
    </c:forEach>
    <c:if test="${result.currentPage!=result.pageCount}">
        <span class="pc">
            <a href="<c:url value='/PageServlet?page=${result.currentPage+1}'></c:url>">下一页</a>
        </span>
    </c:if>
    <br/><br/>
    <!-- 复选框 -->
    <select onchange="sub(this)">
        <c:forEach begin="1" end="${result.pageCount}" var="idx">
            <option <c:if test="${idx==result.currentPage}">selected="selected"</c:if> value="${idx}" >
                第${idx}页
            </option>
        </c:forEach>
    </select>
  </body>
</html>