前段时间学习SSH框架用到分页知识，为此还回顾了一下之前JavaWeb中的分页技术
首先我们先创建一个库和表用来展示分页结果
create table Employee(
empId int(11) NOT NULL AUTO_INCREMENT primary key,
empName varchar(20) NOT NULL,
dept_id int(20) NOT NULL
);
insert into Employee(empName,dept_id) values('aa',1);首先我们准备c3p0-config.xml的配置(在ComboPooledDataSource()初始c3p0连接池会加载这里面的配置信息，连接具体的数据库对象)
<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">123456</property>
<property name="initialPoolSize">3</property>
<property name="maxPoolSize">6</property>
<property name="maxIdleTime">1000</property>
</default-config>1.初始化数据库
2.创建DbUtils核心工具类对象QueryRunner
package cn.itcast.utils;
import javax.sql.DataSource;
import org.apache.commons.dbutils.QueryRunner;
import com.mchange.v2.c3p0.ComboPooledDataSource;
/**
* 工具类
* 1. 初始化C3P0连接池
* 2. 创建DbUtils核心工具类对象
* @author Jie.Yuan
*
*/
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(){
// 创建QueryRunner对象，传入连接池对象
// 在创建QueryRunner对象的时候，如果传入了数据源对象；
// 那么在使用QueryRunner对象方法的时候，就不需要传入连接对象；
// 会自动从数据源中获取连接(不用关闭连接)
return new QueryRunner(dataSource);
}
}
接下来准备实体类，注意由于要用到DbUtils组件，所以实体类中的属性要与数据库的字段一样
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;
}
}数据
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
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 int getTotalPage() {
if(totalCount%pageCount==0){
this.totalCount=totalCount%pageCount;
}else{
this.totalCount=totalCount%pageCount+1;
}
return totalPage;
}
public void setTotalPage(int totalPage) {
this.totalPage = totalPage;
}
public List<T> getPageData() {
return pageData;
}
public void setPageData(List<T> pageData) {
this.pageData = pageData;
}
}public interface UserDao {
public int getTotalCount();
public void getPageData(PageBean<Employee> pb);
}在sql语句中的分页语句是select * from 表 limt ?,?分别是查询的起始行和查询的行数
package cn.itcast.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.itcast.dao.UserDao;
import cn.itcast.entity.Employee;
import cn.itcast.utils.JdbcUtils;
import cn.itcast.utils.PageBean;
public class UserDaoImpl implements UserDao{
@Override
public int getTotalCount() {
String sql="select count(*) from Employee";
try {
QueryRunner qr = JdbcUtils.getQueryRuner();
Long count=qr.query(sql, new ScalarHandler<Long>());
return count.intValue();
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
@Override
public void getPageData(PageBean<Employee> pb) {
int totalCount=getTotalCount();
pb.setTotalCount(totalCount);
if(pb.getCurrentPage()<1){
pb.setCurrentPage(1);
}else if(pb.getCurrentPage()>pb.getTotalPage()){
pb.setCurrentPage(pb.getTotalPage());
}
try {
int first=(pb.getCurrentPage()-1)*pb.getPageCount();
int count=pb.getPageCount();
String sql="select * from Employee limit ?,?";
QueryRunner qr = JdbcUtils.getQueryRuner();
List<Employee> list=qr.query(sql, new BeanListHandler<Employee>(Employee.class),first,count);
pb.setPageData(list);
} catch (SQLException e) {
// TODO Auto-generated catch block
throw new RuntimeException(e);
}
}
}
package cn.itcast.service;
import cn.itcast.entity.Employee;
import cn.itcast.utils.PageBean;
public interface IEmployeeService {
public void getAll(PageBean<Employee> pb);
}
public class UserDaoService implements IEmployeeService{
private UserDao userDao = new UserDaoImpl();
public void getAll(PageBean<Employee> pb) {
userDao.getPageData(pb);
}
}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);
}
}<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!-- 引入jstl核心标签库 -->
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>分页查询数据</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
</head>
<body>
<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>
</body>
</html>