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MyBatis学习——第五篇（手动分页和pagehelper分页实现）

發布時間：2023/12/20 编程问答 20 豆豆

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1：項目場景介紹

在項目中分頁是十分常見的功能，一般使用插件實現分頁功能，但是在使用插件之前我們首先手動寫出分頁代碼，對比插件實現的分頁，利于我們理解分頁底層實現和更好的實現插件分頁實用技術，本次使用的插件是PageHelper（采用都是物理分頁）

在開始之前我們創建兩個表，分別是t_user和person表，并且插入大量的數據。

t_user建表語句：

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建表語句：

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：手動分頁查詢針對user表數據

?項目首頁：

<%@ 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"></head><body><h1>index.jsp</h1><jsp:forward page="/servlet/UserServlet2"><jsp:param value="all" name="method"/></jsp:forward></body> </html>

首先開始我們的手動分頁，核心是一個分頁page類，里面有用于分頁的各種屬性

package com.thit.util;import java.util.List;/*** 抽象出來的分頁類*/ public class PageUtil {private int currentPageNum; //當前要看哪一頁，當前頁private int pageSize=10;//每頁顯示的條數，頁面顯示數據條數private int totalSize;//總記錄條數，總行數private int startIndex;//查詢開始記錄的索引 limit ? ? 開始索引private int totalPageNum;//總頁數private int prePageNum;//上一頁private int nextPageNum;//下一頁private List records;//當前頁的記錄集//用于顯示頁面上的導航的頁號用戶可自定義//開始頁碼private int startPageNum;//結束頁碼private int endPageNum;private String url;//使用構造方法，傳遞必要的兩個參數.第一個是頁碼，第二個總記錄條數public PageUtil(int currentPageNum,int totalrecords){this.currentPageNum=currentPageNum;this.totalSize=totalrecords;//計算開始記錄索引this.startIndex=(currentPageNum-1)*pageSize;//計算總頁數this.totalPageNum=totalSize%pageSize==0?totalSize/pageSize:totalSize/pageSize+1;this.prePageNum=getPrePageNum1();this.nextPageNum=getNextPageNum1();//計算開始和結束頁號這個根據自身可設計if(totalPageNum>9){ //如果總頁數大于9 開始頁面startPageNum=currentPageNum-4;//結束頁面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;}//得到上一頁方法public int getPrePageNum1() {System.out.println("得到上一頁方法");//上一頁等于當前頁減1prePageNum=currentPageNum-1;//如過上一個小于0if(prePageNum<=0){ //上一頁等于1System.out.println("上一頁小于0");prePageNum=1;}return prePageNum;}//得到下一頁方法public int getNextPageNum1() {//下一頁等于當前頁加1System.out.println("得到下一頁的方法");nextPageNum=currentPageNum+1;//如果下一頁大于總頁數if(nextPageNum>totalPageNum){ //下一頁等于總頁數System.out.println("下一頁大于總頁數");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 + ", 上一頁=" + prePageNum+ ", 下一頁=" + 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("首先進入doget");String para=req.getParameter("method");System.out.println("方法參數："+para);if(para.equals("all")) {//查詢所有用戶信息selectAllUsers(req,resp);}}private void selectAllUsers(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubString num=req.getParameter("num");//第一次傳遞 num為空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);//轉發到新的頁面req.getRequestDispatcher("/users.jsp").forward(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubSystem.out.println("首先進入doPost");this.doGet(req, resp);}}

接著是service接口和實現類：

package com.thit.service;import java.util.List;import com.thit.entity.Person; import com.thit.util.PageUtil;public interface Userservice { //查詢userpublic PageUtil getAllusers(String num); //查詢personpublic List<Person> getAllperson(); }-------------------實現類----------------- 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;//如果當前頁不為空，當前頁等于numif(num!=null&&!num.trim().equals("")) {currentPageNum=Integer.parseInt(num);}//查詢總行數方法int totalPageNum=dao.getTotalSize();System.out.println("查詢總行數："+totalPageNum);//當前頁和總行數PageUtil pageUtil=new PageUtil(currentPageNum, totalPageNum);//根據開始下標和行數查詢出來每頁的數據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層和實現類：

package com.thit.dao;import java.util.List;import com.thit.entity.Person; import com.thit.entity.User;public interface Userdao {//手寫分頁查詢user數據List<User> getAllusers(int startIndex,int pagesize) ; //開始索引和頁面條數//查詢表數據條數int getTotalSize();//pagehelper查詢所有person數據List<Person> getAllperson(); }-----------------------dao實現類------------------------ package com.thit.daoimpl;public class Userdaoimpl extends BaseDao implements Userdao {Dbtools dbtools=new Dbtools();//手寫查詢分頁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 {//通過工具類jdbc連接數據庫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;}// 查詢總記錄數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分頁public List<Person> getAllperson() {// mybatis查詢SqlSession sqlsession = dbtools.getSession();PersonMapper personMapper=sqlsession.getMapper(PersonMapper.class);List<Person> lists=personMapper.getAllPersons();return lists;}}

最后的頁面展示代碼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>分頁展示數據</h1><table align="center" width="80%" border="1"><tr><td>id</td><td>username</td><td>address</td></tr><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”) %> 等價于$ { requestScope.userlist } --%>用戶表共${requestScope.page.totalSize}條數據<br>用戶表共${requestScope.page.totalPageNum}頁<br><a href="<%= basePath%>servlet/UserServlet?method=all&num=2">第二頁</a><br><a href="${pageContext.request.contextPath}/servlet/UserServlet?method=all&num=1">首頁</a><a href="${pageContext.request.contextPath}/servlet/UserServlet?method=all&num=${requestScope.page.prePageNum}">上一頁</a><c:forEach begin="${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}">下一頁</a><a href="${pageContext.request.contextPath}/servlet/UserServlet?method=all&num=${requestScope.page.totalPageNum}">末頁</a>跳轉到 <input id="number" type="text" name="hello" size="6">頁<inputtype="button" value="跳轉" onclick="changeNumber()"></input><br><c:forEach begin="6"end="9" var="num"><a href="">${num}</a></c:forEach><script>function changeNumber() {//得到頁碼的具體值var num = document.getElementById("number").value;//是否是數字輸入的數字一定是整數或者是小于總頁數的值window.location.href = "${pageContext.request.contextPath}/servlet/UserServlet?method=all&num="+ num;}</script></div> </body> </html>

手動分頁結果顯示如下：

?3：pegeHelper插件分頁針對user表數據

pegeHelper插件分頁只是幾個部分

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攔截器會攔截查詢方法，并且在查詢的sql中根據不同的數據庫拼接分頁語句實現分頁

第四：將PageInfo這個類存放分頁的各種屬性信息，核心代碼就這三行，num的值由頁面傳遞過來

? ? ? ? ?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><properties resource="db.properties"></properties><typeAliases><package name="com.thit.entity"/></typeAliases><plugins><plugin interceptor="com.github.pagehelper.PageInterceptor"><property name="param1" value="value1"/></plugin></plugins><environments default="demo"><environment id="demo"><transactionManager type="JDBC"></transactionManager><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/PersonMapper.xml"></mapper> </mappers></configuration>---------------------下邊的為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("首先進入doget");String para=req.getParameter("method");System.out.println("方法參數："+para);if(para.equals("all")) {//查詢所有用戶信息selectAllUsers(req,resp);}}private void selectAllUsers(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubString num=req.getParameter("num");//第一次傳遞num為頁數 num為空System.out.println("num的值是："+num);if(null==num) {num="1";}//第二種，Mapper接口方式的調用，頁數和頁面顯示條數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);//轉發到新的頁面req.getRequestDispatcher("/persons.jsp").forward(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubSystem.out.println("首先進入doPost");this.doGet(req, resp);}}

service和dao層在上邊的代碼中已經貼出來了。

頁面展示代碼如下：

<%@ 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"></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${requestScope.pagehelper.total}條/共${requestScope.pagehelper.pages}頁FirstPage<a href="${pageContext.request.contextPath}/servlet/UserServlet2?method=all&num=1">首頁</a><a href="${pageContext.request.contextPath}/servlet/UserServlet2?method=all&num=${requestScope.pagehelper.prePage}">上一頁</a><c:forEach items="${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=${requestScope.pagehelper.nextPage}">下一頁</a><a href="${pageContext.request.contextPath}/servlet/UserServlet2?method=all&num=${requestScope.pagehelper.pages}">末頁</a>跳轉到<input id="number" type="text" name="hello" size="6">頁<input type="button" value="跳轉" onclick="changeNumber()"></input><script>function changeNumber(){var num=document.getElementById("number").value;//是否是數字輸入的數字一定是整數或者是小于總頁數的值window.location.href="${pageContext.request.contextPath}/servlet/UserServlet2?method=all&num="+num;}</script></div></body> </html>

最后的展示效果如下：

總結

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