如果一张表的数据有非常多，页面就需要分页展示，但一次性从数据库中读取全部的数据会给服务器带来巨大压力。jsp分页技术的设计思想来源于“select * from employee limit ?,?”这条sql语句，第一个“？”指查询的起始位置，第二个“？”代表偏移量。页面需要展示多少数据，每次就从服务器读取多少数据，大大减轻了服务器的压力。下面开始实现一个javaweb的demo帮助大家更好的理解。
一.准备工作：
MySQL中创建一张用例表
CREATE TABLE employee( ???empId INT PRIMARY KEY AUTO_INCREMENT, ???empName VARCHAR(20), ???dept_id VARCHAR(20));
往里面插入足够的数据（20条就够了）
二.demo采用mvc模式，首先编写JSP页面
表格代码如下
<table border="1" width="80%" align="center" cellpadding="5" cellspacing="0"> ?????????<tr> ?????????????<td>序号</td> ?????????????<td>员工编号</td> ?????????????<td>员工姓名</td> ?????????</tr> ?????????<!-- 迭代数据 --> ?????????<c:choose> ?????????????<c:when test="${not empty requestScope.pageBean.pageData}"> ?????????????????<c:forEach var="emp" items="${requestScope.pageBean.pageData}" varStatus="vs"> ?????????????????????<tr> ?????????????????????????<td>${vs.count }</td> ?????????????????????????<td>${emp.empId }</td> ?????????????????????????<td>${emp.empName }</td> ?????????????????????</tr> ?????????????????</c:forEach> ?????????????</c:when> ?????????????<c:otherwise> ?????????????????<tr> ?????????????????????<td colspan="3">对不起，没有你要找的数据</td> ?????????????????</tr> ?????????????</c:otherwise> ?????????</c:choose> ???????????????????<tr> ?????????????<td colspan="3" align="center"> ?????????????????当前${requestScope.pageBean.currentPage }/${requestScope.pageBean.totalPage }页 ???? ???????????????????????????????????<a href="${pageContext.request.contextPath }/index?currentPage=1">首页</a> ?????????????????<a href="${pageContext.request.contextPath }/index?currentPage=${requestScope.pageBean.currentPage-1}">上一页 </a> ?????????????????<a href="${pageContext.request.contextPath }/index?currentPage=${requestScope.pageBean.currentPage+1}">下一页 </a> ?????????????????<a href="${pageContext.request.contextPath }/index?currentPage=${requestScope.pageBean.totalPage}">末页</a> ?????????????</td> ?????????</tr> ???????????????</table>三.表对应实体类的设计，分页的几个重要参数也封装到一个实体类里
package cn.cracker.entity;public class Employee { ???private int empId; ???????????// 员工id ???private String empName; ???????// 员工名称 ???private int dept_id; ???????// 部门id ???????public int getEmpId() { ???????return empId; ???} ???public void setEmpId(int empId) { ???????this.empId = empId; ???} ???public String getEmpName() { ???????return empName; ???} ???public void setEmpName(String empName) { ???????this.empName = empName; ???} ???public int getDept_id() { ???????return dept_id; ???} ???public void setDept_id(int deptId) { ???????dept_id = deptId; ???} ???????}package cn.cracker.utils;import java.util.List;import cn.cracker.entity.Employee;public class PageBean<T> { ???private int currentPage = 1; // 当前页, 默认显示第一页 ???private int pageCount = 4; ??// 每页显示的行数(查询返回的行数), 默认每页显示4行 ???private int totalCount; ?????// 总记录数 ???private int totalPage; ??????// 总页数 = 总记录数 / 每页显示的行数 ?(+ 1) ???private List<T> pageData; ??????// 分页查询到的数据 ???????// 返回总页数 ???public int getTotalPage() { ???????if (totalCount % pageCount == 0) { ???????????totalPage = totalCount / pageCount; ???????} else { ???????????totalPage = totalCount / pageCount + 1; ???????} ???????return totalPage; ???} ???public void setTotalPage(int totalPage) { ???????this.totalPage = totalPage; ???} ???????public int getCurrentPage() { ???????return currentPage; ???} ???public void setCurrentPage(int currentPage) { ???????this.currentPage = currentPage; ???} ???public int getPageCount() { ???????return pageCount; ???} ???public void setPageCount(int pageCount) { ???????this.pageCount = pageCount; ???} ???public int getTotalCount() { ???????return totalCount; ???} ???public void setTotalCount(int totalCount) { ???????this.totalCount = totalCount; ???} ???????public List<T> getPageData() { ???????return pageData; ???} ???public void setPageData(List<T> pageData) { ???????this.pageData = pageData; ???} ???????}四.DbUtils和C3p0配置文件
package cn.cracker.utils;import javax.sql.DataSource;import org.apache.commons.dbutils.QueryRunner;import com.mchange.v2.c3p0.ComboPooledDataSource;/** * 工具类 */public class JdbcUtils { ???/** ????* ?1. 初始化C3P0连接池 ????*/ ???private static ?DataSource dataSource; ???static { ???????dataSource = new ComboPooledDataSource(); ???} ???????/** ????* 2. 创建DbUtils核心工具类对象 ????*/ ???public static QueryRunner getQueryRuner(){ ???????return new QueryRunner(dataSource); ???}}<c3p0-config> ???<default-config> ???????<property name="jdbcUrl">jdbc:mysql://localhost:3306/jdbc_demo ???????</property> ???????<property name="driverClass">com.mysql.jdbc.Driver</property> ???????<property name="user">root</property> ???????<property name="password">root</property> ???????<property name="initialPoolSize">3</property> ???????<property name="maxPoolSize">6</property> ???????<property name="maxIdleTime">1000</property> ???</default-config> ???<named-config name="oracle_config"> ???????<property name="jdbcUrl">jdbc:mysql://localhost:3306/jdbc_demo</property> ???????<property name="driverClass">com.mysql.jdbc.Driver</property> ???????<property name="user">root</property> ???????<property name="password">root</property> ???????<property name="initialPoolSize">3</property> ???????<property name="maxPoolSize">6</property> ???????<property name="maxIdleTime">1000</property> ???</named-config></c3p0-config>
五.数据库访问层的设计(包含接口与实现)
实现查询分页的数据和总数据两个功能
package cn.cracker.dao;import cn.cracker.entity.Employee;import cn.cracker.utils.PageBean;public interface IEmployeeDao { ???public void getAll(PageBean<Employee> pb); ???????public int getTotalCount();}package cn.cracker.dao.impl;import java.sql.SQLException;import java.util.List;import org.apache.commons.dbutils.QueryRunner;import org.apache.commons.dbutils.handlers.BeanListHandler;import org.apache.commons.dbutils.handlers.ScalarHandler;import cn.cracker.dao.IEmployeeDao;import cn.cracker.entity.Employee;import cn.cracker.utils.JdbcUtils;import cn.cracker.utils.PageBean;/** * 2. 数据访问层实现 */public class EmployeeDao implements IEmployeeDao { ???@Override ???public void getAll(PageBean<Employee> pb) { ???????????????//2. 查询总记录数; ?设置到pb对象中 ???????int totalCount = this.getTotalCount(); ???????pb.setTotalCount(totalCount); ???????????????/* ????????* 问题： jsp页面，如果当前页为首页，再点击上一页报错！ ????????* ?????????????如果当前页为末页，再点下一页显示有问题！ ????????* 解决： ????????* ???????1. 如果当前页 <= 0; ??????当前页设置当前页为1; ????????* ???????2. 如果当前页 > 最大页数； ?当前页设置为最大页数 ????????*/ ???????// 判断 ???????if (pb.getCurrentPage() <=0) { ???????????pb.setCurrentPage(1); ???????????????????????// 把当前页设置为1 ???????} else if (pb.getCurrentPage() > pb.getTotalPage()){ ???????????pb.setCurrentPage(pb.getTotalPage()); ???????// 把当前页设置为最大页数 ???????} ???????????????//1. 获取当前页： 计算查询的起始行、返回的行数 ???????int currentPage = pb.getCurrentPage(); ???????int index = (currentPage -1 ) * pb.getPageCount(); ???????// 查询的起始行 ???????int count = pb.getPageCount(); ???????????????????????????// 查询返回的行数 ???????????????????????//3. 分页查询数据; ?把查询到的数据设置到pb对象中 ???????String sql = "select * from employee limit ?,?"; ???????????????try { ???????????// 得到Queryrunner对象 ???????????QueryRunner qr = JdbcUtils.getQueryRuner(); ???????????// 根据当前页，查询当前页数据(一页数据) ???????????List<Employee> pageData = qr.query(sql, new BeanListHandler<Employee>(Employee.class), index, count); ???????????// 设置到pb对象中 ???????????pb.setPageData(pageData); ???????????????????} catch (Exception e) { ???????????throw new RuntimeException(e); ???????} ???????????} ???@Override ???public int getTotalCount() { ???????String sql = "select count(*) from employee"; ???????try { ???????????// 创建QueryRunner对象 ???????????QueryRunner qr = JdbcUtils.getQueryRuner(); ???????????// 执行查询， 返回结果的第一行的第一列 ???????????Long count = qr.query(sql, new ScalarHandler<Long>()); ???????????return count.intValue(); ???????} catch (Exception e) { ???????????throw new RuntimeException(e); ???????} ???}}六.业务层
package cn.cracker.service;import cn.cracker.entity.Employee;import cn.cracker.utils.PageBean;public interface IEmployeeService { ???/** ????* 分页查询数据 ????*/ ???public void getAll(PageBean<Employee> pb);}package cn.cracker.service.impl;import cn.cracker.dao.IEmployeeDao;import cn.cracker.dao.impl.EmployeeDao;import cn.cracker.entity.Employee;import cn.cracker.service.IEmployeeService;import cn.cracker.utils.PageBean;/** * 3. 业务逻辑层，实现 */public class EmployeeService implements IEmployeeService { ???????// 创建Dao实例 ???private IEmployeeDao employeeDao = new EmployeeDao(); ???@Override ???public void getAll(PageBean<Employee> pb) { ???????try { ???????????employeeDao.getAll(pb); ???????} catch (Exception e) { ???????????throw new RuntimeException(e); ???????} ???}}七.控制层
package cn.cracker.servlet;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import cn.cracker.entity.Employee;import cn.cracker.service.IEmployeeService;import cn.cracker.service.impl.EmployeeService;import cn.cracker.utils.PageBean;/** * 4. 控制层开发 */public class IndexServlet extends HttpServlet { ???// 创建Service实例 ???private IEmployeeService employeeService = new EmployeeService(); ???// 跳转资源 ???private String uri; ???public void doGet(HttpServletRequest request, HttpServletResponse response) ???????????throws ServletException, IOException { ???????????????try { ???????????//1. 获取“当前页”参数； ?(第一次访问当前页为null) ????????????String currPage = request.getParameter("currentPage"); ???????????// 判断 ???????????if (currPage == null || "".equals(currPage.trim())){ ???????????????currPage = "1"; ?????// 第一次访问，设置当前页为1; ???????????} ???????????// 转换 ???????????int currentPage = Integer.parseInt(currPage); ???????????????????????//2. 创建PageBean对象，设置当前页参数； 传入service方法参数 ???????????PageBean<Employee> pageBean = new PageBean<Employee>(); ???????????pageBean.setCurrentPage(currentPage); ???????????????????????//3. 调用service ?????????????employeeService.getAll(pageBean); ???// 【pageBean已经被dao填充了数据】 ???????????????????????//4. 保存pageBean对象，到request域中 ???????????request.setAttribute("pageBean", pageBean); ???????????????????????//5. 跳转 ????????????uri = "/WEB-INF/list.jsp"; ???????} catch (Exception e) { ???????????e.printStackTrace(); ?// 测试使用 ???????????// 出现错误，跳转到错误页面；给用户友好提示 ???????????uri = "/error/error.jsp"; ???????} ???????request.getRequestDispatcher(uri).forward(request, response); ???????????} ???public void doPost(HttpServletRequest request, HttpServletResponse response) ???????????throws ServletException, IOException { ???????this.doGet(request, response); ???}}PS：别忘了导入这几个lib包 c3p0-0.9.1.2.jar、commons-dbutils-1.6.jar、mysql-connector-java-5.1.12-bin.jar
jsp分页技术
原文地址：https://www.cnblogs.com/cracker13/p/9420468.html