1：项目场景介绍

在项目中分页是十分常见的功能，一般使用插件实现分页功能，但是在使用插件之前我们首先手动写出分页代码，对比插件实现的分页，利于我们理解分页底层实现和更好的实现插件分页实用技术，本次使用的插件是PageHelper（采用都是物理分页）

在开始之前我们创建两个表，分别是t_user和person表，并且插入大量的数据。

t_user建表语句：

CREATE TABLE `t_user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(255) DEFAULT NULL,
`password` varchar(255) DEFAULT NULL,
`address` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

person建表语句：

CREATE TABLE `person` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(255) DEFAULT NULL,
`email` varchar(255) DEFAULT NULL,
`gender` varchar(255) DEFAULT NULL,
`dept_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

2：手动分页查询针对user表数据

项目首页：

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><base href="<%=basePath%>"><title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--></head><body><h1>index.jsp</h1><jsp:forward page="/servlet/UserServlet2"><jsp:param value="all" name="method"/></jsp:forward></body>
</html>

首先开始我们的手动分页，核心是一个分页page类，里面有用于分页的各种属性

package com.thit.util;import java.util.List;/*** 抽象出来的分页类*/
public class PageUtil {private int currentPageNum; //当前要看哪一页，当前页private int pageSize=10;//每页显示的条数，页面显示数据条数private int totalSize;//总记录条数，总行数private int startIndex;//查询开始记录的索引 limit ? ? 开始索引private int totalPageNum;//总页数private int prePageNum;//上一页private int nextPageNum;//下一页private List  records;//当前页的记录集//用于显示页面上的导航的页号  用户可自定义//开始页码private int startPageNum;//结束页码private int endPageNum;private String url;//使用构造方法，传递必要的两个参数.第一个是页码，第二个总记录条数public PageUtil(int currentPageNum,int totalrecords){this.currentPageNum=currentPageNum;this.totalSize=totalrecords;//计算开始记录索引this.startIndex=(currentPageNum-1)*pageSize;//计算总页数this.totalPageNum=totalSize%pageSize==0?totalSize/pageSize:totalSize/pageSize+1;this.prePageNum=getPrePageNum1();this.nextPageNum=getNextPageNum1();//计算开始和结束页号  这个根据自身可设计if(totalPageNum>9){    //如果总页数大于9 开始页面startPageNum=currentPageNum-4;//结束页面endPageNum=currentPageNum+4;if(startPageNum<1){startPageNum=1;endPageNum=startPageNum+8;}if(endPageNum>totalPageNum){endPageNum=totalPageNum;startPageNum=endPageNum-8;}}else{startPageNum=1;endPageNum=totalPageNum;}}public int getStartPageNum() {return startPageNum;}public void setStartPageNum(int startPageNum) {this.startPageNum = startPageNum;}public int getEndPageNum() {return endPageNum;}public void setEndPageNum(int endPageNum) {this.endPageNum = endPageNum;}//得到上一页方法public int getPrePageNum1() {System.out.println("得到上一页方法");//上一页等于当前页减1prePageNum=currentPageNum-1;//如过上一个小于0if(prePageNum<=0){ //上一页等于1System.out.println("上一页小于0");prePageNum=1;}return prePageNum;}//得到下一页方法public int getNextPageNum1() {//下一页等于当前页加1System.out.println("得到下一页的方法");nextPageNum=currentPageNum+1;//如果下一页大于总页数if(nextPageNum>totalPageNum){    //下一页等于总页数System.out.println("下一页大于总页数");nextPageNum=totalPageNum;}return nextPageNum;}public int getPrePageNum() {return prePageNum;}public int getNextPageNum() {return nextPageNum;}public int getCurrentPageNum() {return currentPageNum;}public void setCurrentPageNum(int currentPageNum) {this.currentPageNum = currentPageNum;}public int getPageSize() {return pageSize;}public void setPageSize(int pageSize) {this.pageSize = pageSize;}public int getTotalSize() {return totalSize;}public void setTotalSize(int totalSize) {this.totalSize = totalSize;}public int getStartIndex() {return startIndex;}public void setStartIndex(int startIndex) {this.startIndex = startIndex;}public int getTotalPageNum() {return totalPageNum;}public void setTotalPageNum(int totalPageNum) {this.totalPageNum = totalPageNum;}public List  getRecords() {return records;}public void setRecords(List  records) {this.records = records;}public void setPrePageNum(int prePageNum) {this.prePageNum = prePageNum;}public void setNextPageNum(int nextPageNum) {this.nextPageNum = nextPageNum;}public String getUrl() {return url;}public void setUrl(String url) {this.url = url;}@Overridepublic String toString() {return "PageUtil [currentPageNum=" + currentPageNum + ", pageSize=" + pageSize + ", totalSize=" + totalSize+ ", startIndex=" + startIndex + ", totalPageNum=" + totalPageNum + ", 上一页=" + prePageNum+ ", 下一页=" + nextPageNum + ", records=" + records + ", startPageNum=" + startPageNum+ ", endPageNum=" + endPageNum + ", url=" + url + "]";}}

然后是Servlet:

package com.thit.web;
import java.io.IOException;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import com.thit.service.Userservice;
import com.thit.serviceimpl.UserserviceImpl;
import com.thit.util.PageUtil;@WebServlet("/servlet/UserServlet")
public class UserServlet  extends HttpServlet{Userservice userservice=new UserserviceImpl();/*** */private static final long serialVersionUID = 1L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubSystem.out.println("首先进入doget");String para=req.getParameter("method");System.out.println("方法参数："+para);if(para.equals("all")) {//查询所有用户信息selectAllUsers(req,resp);}}private void selectAllUsers(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubString num=req.getParameter("num");//第一次传递 num为空System.out.println("num的值是："+num);if(null==num) {num="1";}PageUtil page=userservice.getAllusers(num);System.out.println(page.toString());req.setAttribute("page",page);//转发到新的页面req.getRequestDispatcher("/users.jsp").forward(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubSystem.out.println("首先进入doPost");this.doGet(req, resp);}}

接着是service接口和实现类：

package com.thit.service;import java.util.List;import com.thit.entity.Person;
import com.thit.util.PageUtil;public interface Userservice {
//查询userpublic PageUtil getAllusers(String num);
//查询personpublic List<Person> getAllperson();
}-------------------实现类-----------------
package com.thit.serviceimpl;import java.util.List;import org.apache.commons.dbutils.DbUtils;import com.thit.dao.Userdao;
import com.thit.daoimpl.Userdaoimpl;
import com.thit.entity.Person;
import com.thit.entity.User;
import com.thit.service.Userservice;
import com.thit.util.PageUtil;public class UserserviceImpl implements Userservice {Userdao dao=new Userdaoimpl();public PageUtil getAllusers(String num) {// TODO Auto-generated method stubint currentPageNum=1;//如果当前页不为空，当前页等于numif(num!=null&&!num.trim().equals("")) {currentPageNum=Integer.parseInt(num);}//查询总行数方法int totalPageNum=dao.getTotalSize();System.out.println("查询总行数："+totalPageNum);//当前页 和 总行数PageUtil pageUtil=new PageUtil(currentPageNum, totalPageNum);//根据开始下标和行数查询出来每页的数据List<User> list=dao.getAllusers(pageUtil.getStartIndex(), pageUtil.getPageSize());for(User u:list) {System.out.println(u);}pageUtil.setRecords(list);return pageUtil;}public List<Person> getAllperson() {List<Person> lists=dao.getAllperson();return lists;}}

dao层和实现类：

package com.thit.dao;import java.util.List;import com.thit.entity.Person;
import com.thit.entity.User;public interface Userdao {//手写分页查询user数据List<User> getAllusers(int startIndex,int pagesize) ; //开始索引和页面条数//查询表数据条数int getTotalSize();//pagehelper查询所有person数据List<Person> getAllperson();
}-----------------------dao实现类------------------------
package com.thit.daoimpl;public class Userdaoimpl extends BaseDao implements Userdao {Dbtools dbtools=new Dbtools();//手写查询分页public List<User> getAllusers(int startIndex, int pagesize) {// TODO Auto-generated method stubString sql = "select  * from t_user limit ?,?";List<User> lists = new ArrayList<User>();try {//通过工具类jdbc连接数据库Connection connection = getConnection();PreparedStatement pStatement = connection.prepareStatement(sql);pStatement.setInt(1, startIndex);pStatement.setInt(2, pagesize);ResultSet re = pStatement.executeQuery();while (re.next()) {int id = re.getInt("id");String username = re.getString("username");String password = re.getString("password");String address = re.getString("address");User user = new User(id, username, address);lists.add(user);}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}return lists;}// 查询总记录数public int getTotalSize() {// TODO Auto-generated method stubint count=0;try {String sql = "select count(*) as num from t_user";Connection connection = getConnection();PreparedStatement pStatement = connection.prepareStatement(sql);ResultSet re = pStatement.executeQuery();while (re.next()) {count= re.getInt("num");}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}return count;}//pagehelper分页public List<Person> getAllperson() {// mybatis查询SqlSession sqlsession = dbtools.getSession();PersonMapper personMapper=sqlsession.getMapper(PersonMapper.class);List<Person> lists=personMapper.getAllPersons();return lists;}}

最后的页面展示代码jsp如下：

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%String path = request.getContextPath();String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort()+ path + "/";System.out.println("path:"+path);System.out.println("basePath:"+basePath);%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>"><title>My JSP 'users.jsp' starting page</title><meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
</head><body><h1>分页展示数据</h1><table align="center" width="80%" border="1"><tr><td>id</td><td>username</td><td>address</td></tr><!--在请求域中 是EL表达式中的一个隐含对象，类似request，如：${requestScope.username} 表示在request域中取得username属性所对应的值，相当于request.getAttribute(“username”)。 --><c:forEach items="${requestScope.page.records}" var="user"><tr><td>${user.id}</td><td>${user.username}</td><td>${user.address}</td></tr><br></c:forEach></table><div align="center"><%-- <%=request.getAttribute(“userlist”) %> 等价于$ { requestScope.userlist } --%>用户表共${requestScope.page.totalSize}条数据<br>用户表共${requestScope.page.totalPageNum}页<br><a href="<%= basePath%>servlet/UserServlet?method=all&num=2">第二页</a><br><a href="${pageContext.request.contextPath}/servlet/UserServlet?method=all&num=1">首页</a><a href="${pageContext.request.contextPath}/servlet/UserServlet?method=all&num=${requestScope.page.prePageNum}">上一页</a><c:forEach begin="${requestScope.page.startPageNum}"end="${requestScope.page.endPageNum}" var="num"><a href="${pageContext.request.contextPath}/servlet/UserServlet?method=all&num=${num}">${num}</a></c:forEach><a href="${pageContext.request.contextPath}/servlet/UserServlet?method=all&num=${requestScope.page.nextPageNum}">下一页</a><a href="${pageContext.request.contextPath}/servlet/UserServlet?method=all&num=${requestScope.page.totalPageNum}">末页</a>跳转到 <input id="number" type="text" name="hello" size="6">页<inputtype="button" value="跳转" onclick="changeNumber()"></input><br><c:forEach begin="6"end="9" var="num"><a href="">${num}</a></c:forEach><script>function changeNumber() {//得到页码的具体值var num = document.getElementById("number").value;//是否是数字  输入的数字一定是整数或者是小于总页数的值window.location.href = "${pageContext.request.contextPath}/servlet/UserServlet?method=all&num="+ num;}</script></div>
</body>
</html>

手动分页结果显示如下：

3：pegeHelper插件分页针对user表数据

pegeHelper插件分页只是几个部分

第一：需要的mybatis的配置文件中配置插件

第二：在servlect中使用PageHelper的startPage方法

第三：PageHelper拦截器会拦截查询方法，并且在查询的sql中根据不同的数据库拼接分页语句实现分页

第四：将PageInfo这个类存放分页的各种属性信息，核心代码就这三行，num的值由页面传递过来

Page<Object> page=PageHelper.startPage(Integer.valueOf(num), 10)；
List<Person> persons=userservice.getAllperson();
PageInfo<?> pageHepler=page.toPageInfo();

需要添加mybatis配置文件和mapper

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><!-- plugins在配置文件中的位置必须符合要求，否则会报错，顺序如下:properties?, settings?, typeAliases?, typeHandlers?, objectFactory?,objectWrapperFactory?, plugins?, environments?, databaseIdProvider?, mappers?
--><properties resource="db.properties"></properties><typeAliases><package name="com.thit.entity"/></typeAliases><!--配置插件  --><plugins><!-- com.github.pagehelper为PageHelper类所在包名 --><plugin interceptor="com.github.pagehelper.PageInterceptor"><!-- 使用下面的方式配置参数，后面会有所有的参数介绍 --><property name="param1" value="value1"/></plugin></plugins><environments default="demo"><environment id="demo"><!-- type="JDBC" 代表使用JDBC的提交和回滚来管理事务 --><transactionManager type="JDBC"></transactionManager><!-- mybatis提供了3种数据源类型，分别是：POOLED,UNPOOLED,JNDI --><!-- POOLED 表示支持JDBC数据源连接池 --><!-- UNPOOLED 表示不支持数据源连接池 --><!-- JNDI 表示支持外部数据源连接池 --><dataSource type="POOLED"><property name="driver" value="${mysqldriver}"/><property name="url" value="${mysqlurl}"/><property name="username" value="${mysqlusername}"/><property name="password" value="${mysqlpassword}"/></dataSource></environment>
</environments><mappers><!-- <mapper resource="mapper/userMapper.xml"/> --><mapper resource="mapper/PersonMapper.xml"></mapper> <!--   <mapper class="com.thit.dao.PersonMapper"/> --></mappers></configuration>---------------------下边的为PersonMapper配置文件-----------------
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.thit.dao.PersonMapper"><select id="getAllPersons" resultType="Person">select * from person</select></mapper>

然后servlet如下：

package com.thit.web;import java.io.IOException;
import java.util.List;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import com.github.pagehelper.Page;
import com.github.pagehelper.PageHelper;
import com.github.pagehelper.PageInfo;
import com.thit.entity.Person;
import com.thit.service.Userservice;
import com.thit.serviceimpl.UserserviceImpl;
import com.thit.util.PageUtil;@WebServlet("/servlet/UserServlet2")
public class UserServlet2  extends HttpServlet{Userservice userservice=new UserserviceImpl();/*** */private static final long serialVersionUID = 1L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubSystem.out.println("首先进入doget");String para=req.getParameter("method");System.out.println("方法参数："+para);if(para.equals("all")) {//查询所有用户信息selectAllUsers(req,resp);}}private void selectAllUsers(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubString num=req.getParameter("num");//第一次传递num为页数  num为空System.out.println("num的值是："+num);if(null==num) {num="1";}//第二种，Mapper接口方式的调用，页数和页面显示条数Page<Object> page=PageHelper.startPage(Integer.valueOf(num), 10);List<Person> persons=userservice.getAllperson();PageInfo<?> pageHepler=page.toPageInfo();req.setAttribute("persons", persons);req.setAttribute("pagehelper", pageHepler);//转发到新的页面req.getRequestDispatcher("/persons.jsp").forward(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubSystem.out.println("首先进入doPost");this.doGet(req, resp);}}

service和dao层在上边的代码中已经贴出来了。

页面展示代码如下：

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core"  prefix="c"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><base href="<%=basePath%>"><title>My JSP 'users.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--></head><body><table align="center" width="80%" border="1"><tr><td>id</td><td>username</td><td>address</td></tr><c:forEach items="${requestScope.persons}" var="person"><tr><td>${person.id} </td><td>${person.username}</td><td>${person.email}</td></tr><br></c:forEach></table><div align="center">共${requestScope.pagehelper.total}条/共${requestScope.pagehelper.pages}页FirstPage<a href="${pageContext.request.contextPath}/servlet/UserServlet2?method=all&num=1">首页</a><a href="${pageContext.request.contextPath}/servlet/UserServlet2?method=all&num=${requestScope.pagehelper.prePage}">上一页</a><c:forEach   items="${requestScope.pagehelper.navigatepageNums}" var="num"><a href="${pageContext.request.contextPath}/servlet/UserServlet2?method=all&num=${num}">${num}</a></c:forEach><a href="${pageContext.request.contextPath}/servlet/UserServlet2?method=all&num=${requestScope.pagehelper.nextPage}">下一页</a><a href="${pageContext.request.contextPath}/servlet/UserServlet2?method=all&num=${requestScope.pagehelper.pages}">末页</a>跳转到<input id="number" type="text" name="hello" size="6">页<input type="button" value="跳转" onclick="changeNumber()"></input><script>function changeNumber(){var num=document.getElementById("number").value;//是否是数字  输入的数字一定是整数或者是小于总页数的值window.location.href="${pageContext.request.contextPath}/servlet/UserServlet2?method=all&num="+num;}</script></div></body>
</html>

最后的展示效果如下：

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前言:

MyBatis学习——第五篇（手动分页和pagehelper分页实现）

1：项目场景介绍

2：手动分页查询针对user表数据

3：pegeHelper插件分页针对user表数据

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