在项目中分页是十分常见的功能&＃xff0c;一般使用插件实现分页功能&＃xff0c;但是在使用插件之前我们首先手动写出分页代码&＃xff0c;对比插件实现的分页&＃xff0c;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&＃xff0c;本次使用的插件是PageHelper&＃xff08;采用都是物理分页&＃xff09;

在开始之前我们创建两个表&＃xff0c;分别是t_user和person表&＃xff0c;并且插入大量的数据。

t_user建表语句&＃xff1a;

CREATE TABLE &＃96;t_user&＃96; (
  &＃96;id&＃96; int(11) NOT NULL AUTO_INCREMENT,
  &＃96;username&＃96; varchar(255) DEFAULT NULL,
  &＃96;password&＃96; varchar(255) DEFAULT NULL,
  &＃96;address&＃96; varchar(255) DEFAULT NULL,
  PRIMARY KEY (&＃96;id&＃96;)
) ENGINE&＃61;InnoDB  DEFAULT CHARSET&＃61;utf8;

person建表语句&＃xff1a;

CREATE TABLE &＃96;person&＃96; (
  &＃96;id&＃96; int(11) NOT NULL AUTO_INCREMENT,
  &＃96;username&＃96; varchar(255) DEFAULT NULL,
  &＃96;email&＃96; varchar(255) DEFAULT NULL,
  &＃96;gender&＃96; varchar(255) DEFAULT NULL,
  &＃96;dept_id&＃96; int(11) DEFAULT NULL,
  PRIMARY KEY (&＃96;id&＃96;)
) ENGINE&＃61;InnoDB  DEFAULT CHARSET&＃61;utf8;

 项目首页&＃xff1a;

<%&＃64; page language&＃61;"java" import&＃61;"java.util.*" pageEncoding&＃61;"utf-8"%>
<%
String path &＃61; request.getContextPath();
String basePath &＃61; request.getScheme()&＃43;"://"&＃43;request.getServerName()&＃43;":"&＃43;request.getServerPort()&＃43;path&＃43;"/";
%>
">

index.jsp

首先开始我们的手动分页&＃xff0c;核心是一个分页page类&＃xff0c;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&＃xff0c;当前页private int pageSize&＃61;10;//每页显示的条数&＃xff0c;页面显示数据条数private int totalSize;//总记录条数&＃xff0c;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&＃xff0c;传递必要的两个参数.第一个是页码&＃xff0c;第二个总记录条数public PageUtil(int currentPageNum,int totalrecords){this.currentPageNum&＃61;currentPageNum;this.totalSize&＃61;totalrecords;//计算开始记录索引this.startIndex&＃61;(currentPageNum-1)*pageSize;//计算总页数this.totalPageNum&＃61;totalSize%pageSize&＃61;&＃61;0?totalSize/pageSize:totalSize/pageSize&＃43;1;this.prePageNum&＃61;getPrePageNum1();this.nextPageNum&＃61;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&＃61;currentPageNum-4;//结束页面endPageNum&＃61;currentPageNum&＃43;4;if(startPageNum<1){startPageNum&＃61;1;endPageNum&＃61;startPageNum&＃43;8;}if(endPageNum>totalPageNum){endPageNum&＃61;totalPageNum;startPageNum&＃61;endPageNum-8;}}else{startPageNum&＃61;1;endPageNum&＃61;totalPageNum;}}public int getStartPageNum() {return startPageNum;}public void setStartPageNum(int startPageNum) {this.startPageNum &＃61; startPageNum;}public int getEndPageNum() {return endPageNum;}public void setEndPageNum(int endPageNum) {this.endPageNum &＃61; 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&＃61;currentPageNum-1;//如过上一个小于0if(prePageNum<&＃61;0){ //上一页等于1System.out.println("上一页小于0");prePageNum&＃61;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&＃61;currentPageNum&＃43;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&＃61;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 &＃61; currentPageNum;}public int getPageSize() {return pageSize;}public void setPageSize(int pageSize) {this.pageSize &＃61; pageSize;}public int getTotalSize() {return totalSize;}public void setTotalSize(int totalSize) {this.totalSize &＃61; totalSize;}public int getStartIndex() {return startIndex;}public void setStartIndex(int startIndex) {this.startIndex &＃61; startIndex;}public int getTotalPageNum() {return totalPageNum;}public void setTotalPageNum(int totalPageNum) {this.totalPageNum &＃61; totalPageNum;}public List getRecords() {return records;}public void setRecords(List records) {this.records &＃61; records;}public void setPrePageNum(int prePageNum) {this.prePageNum &＃61; prePageNum;}public void setNextPageNum(int nextPageNum) {this.nextPageNum &＃61; nextPageNum;}public String getUrl() {return url;}public void setUrl(String url) {this.url &＃61; url;}&＃64;Overridepublic String toString() {return "PageUtil [currentPageNum&＃61;" &＃43; currentPageNum &＃43; ", pageSize&＃61;" &＃43; pageSize &＃43; ", totalSize&＃61;" &＃43; totalSize&＃43; ", startIndex&＃61;" &＃43; startIndex &＃43; ", totalPageNum&＃61;" &＃43; totalPageNum &＃43; ", 上一页&＃61;" &＃43; prePageNum&＃43; ", 下一页&＃61;" &＃43; nextPageNum &＃43; ", records&＃61;" &＃43; records &＃43; ", startPageNum&＃61;" &＃43; startPageNum&＃43; ", endPageNum&＃61;" &＃43; endPageNum &＃43; ", url&＃61;" &＃43; url &＃43; "]";}}


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;&＃64;WebServlet("/servlet/UserServlet")
public class UserServlet extends HttpServlet{Userservice userservice&＃61;new UserserviceImpl();/*** */private static final long serialVersionUID &＃61; 1L;&＃64;Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubSystem.out.println("首先进入doget");String para&＃61;req.getParameter("method");System.out.println("方法参数&＃xff1a;"&＃43;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&＃61;req.getParameter("num");//第一次传递 num为空System.out.println("num的值是&＃xff1a;"&＃43;num);if(null&＃61;&＃61;num) {num&＃61;"1";}PageUtil page&＃61;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);}&＃64;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&＃xff1a;

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 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&＃61;new Userdaoimpl();public PageUtil getAllusers(String num) {// TODO Auto-generated method stubint currentPageNum&＃61;1;//如果当前页不为空&＃xff0c;当前页等于numif(num!&＃61;null&&!num.trim().equals("")) {currentPageNum&＃61;Integer.parseInt(num);}//查询总行数方法int totalPageNum&＃61;dao.getTotalSize();System.out.println("查询总行数&＃xff1a;"&＃43;totalPageNum);//当前页 和 总行数PageUtil pageUtil&＃61;new PageUtil(currentPageNum, totalPageNum);//根据开始下标和行数查询出来每页的数据List list&＃61;dao.getAllusers(pageUtil.getStartIndex(), pageUtil.getPageSize());for(User u:list) {System.out.println(u);}pageUtil.setRecords(list);return pageUtil;}public List getAllperson() {List lists&＃61;dao.getAllperson();return lists;}}


dao层和实现类&＃xff1a;

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 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 getAllperson();
}-----------------------dao实现类------------------------
package com.thit.daoimpl;public class Userdaoimpl extends BaseDao implements Userdao {Dbtools dbtools&＃61;new Dbtools();//手写查询分页public List getAllusers(int startIndex, int pagesize) {// TODO Auto-generated method stubString sql &＃61; "select * from t_user limit ?,?";List lists &＃61; new ArrayList();try {//通过工具类jdbc连接数据库Connection connection &＃61; getConnection();PreparedStatement pStatement &＃61; connection.prepareStatement(sql);pStatement.setInt(1, startIndex);pStatement.setInt(2, pagesize);ResultSet re &＃61; pStatement.executeQuery();while (re.next()) {int id &＃61; re.getInt("id");String username &＃61; re.getString("username");String password &＃61; re.getString("password");String address &＃61; re.getString("address");User user &＃61; 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&＃61;0;try {String sql &＃61; "select count(*) as num from t_user";Connection connection &＃61; getConnection();PreparedStatement pStatement &＃61; connection.prepareStatement(sql);ResultSet re &＃61; pStatement.executeQuery();while (re.next()) {count&＃61; re.getInt("num");}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}return count;}//pagehelper分页public List getAllperson() {// mybatis查询SqlSession sqlsession &＃61; dbtools.getSession();PersonMapper personMapper&＃61;sqlsession.getMapper(PersonMapper.class);List lists&＃61;personMapper.getAllPersons();return lists;}}

最后的页面展示代码jsp如下&＃xff1a;

<%&＃64; page language&＃61;"java" import&＃61;"java.util.*" pageEncoding&＃61;"utf-8"%>
<%&＃64; taglib uri&＃61;"http://java.sun.com/jsp/jstl/core" prefix&＃61;"c"%>
<%String path &＃61; request.getContextPath();String basePath &＃61; request.getScheme() &＃43; "://" &＃43; request.getServerName() &＃43; ":" &＃43; request.getServerPort()&＃43; path &＃43; "/";System.out.println("path:"&＃43;path);System.out.println("basePath:"&＃43;basePath);%>


">






分页展示数据

手动分页结果显示如下&＃xff1a;

pegeHelper插件分页只是几个部分

第一&＃xff1a;需要的mybatis的配置文件中配置插件

第二&＃xff1a;在servlect中使用PageHelper的startPage方法

第三&＃xff1a;PageHelper拦截器会拦截查询方法&＃xff0c;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&＃xff1a;将PageInfo这个类存放分页的各种属性信息&＃xff0c;核心代码就这三行&＃xff0c;num的值由页面传递过来

         Page page&＃61;PageHelper.startPage(Integer.valueOf(num), 10)&＃xff1b;
         List persons&＃61;userservice.getAllperson();
         PageInfo pageHepler&＃61;page.toPageInfo();

需要添加mybatis配置文件和mapper


PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">

---------------------下边的为PersonMapper配置文件-----------------


select * from person

然后servlet如下&＃xff1a;

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;&＃64;WebServlet("/servlet/UserServlet2")
public class UserServlet2 extends HttpServlet{Userservice userservice&＃61;new UserserviceImpl();/*** */private static final long serialVersionUID &＃61; 1L;&＃64;Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubSystem.out.println("首先进入doget");String para&＃61;req.getParameter("method");System.out.println("方法参数&＃xff1a;"&＃43;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&＃61;req.getParameter("num");//第一次传递num为页数 num为空System.out.println("num的值是&＃xff1a;"&＃43;num);if(null&＃61;&＃61;num) {num&＃61;"1";}//第二种&＃xff0c;Mapper接口方式的调用&＃xff0c;页数和页面显示条数Page page&＃61;PageHelper.startPage(Integer.valueOf(num), 10);List persons&＃61;userservice.getAllperson();PageInfo pageHepler&＃61;page.toPageInfo();req.setAttribute("persons", persons);req.setAttribute("pagehelper", pageHepler);//转发到新的页面req.getRequestDispatcher("/persons.jsp").forward(req, resp);}&＃64;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&＃xff1a;

<%&＃64; page language&＃61;"java" import&＃61;"java.util.*" pageEncoding&＃61;"utf-8"%>
<%&＃64; taglib uri&＃61;"http://java.sun.com/jsp/jstl/core" prefix&＃61;"c"%>
<%
String path &＃61; request.getContextPath();
String basePath &＃61; request.getScheme()&＃43;"://"&＃43;request.getServerName()&＃43;":"&＃43;request.getServerPort()&＃43;path&＃43;"/";
%>
">

最后的展示效果如下&＃xff1a;