Java基础94 分页查询（以MySQL数据库为例）

1、概述

分页查询，也可叫做分批查询，基于数据库的分页语句(不同数据库是不同的)。
  本文使用的事MySql数据库。
       假设：每页显示10条数据.
       Select * from contact  limit M,N;
       M：开始记录的索引。第一条数据的索引为0 （页数）
       N：一次查询几条记录（每页显示的数据的条数）
           则：
             第一页：select * from contact limit 0,10;
             第二页：select * from contact limit 10,10
             ............
             第n页：select * from contact limit(M-1)*N,N;

在MySQL数据库中的分页查询操作：https://www.cnblogs.com/dshore123/p/10544241.html

2、实例演示

db.properties 配置文件

 url=jdbc:mysql://localhost:3306/school
 user=root
 password=123456
 driverClass=com.mysql.jdbc.Driver

JdbcUtil.java 封装文件（连接数据库）

 package com.shore.util;

 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.Properties;

 public class JdbcUtil {
     //连接数据库的URL
     private static String url=null;
     private static String user=null;//用户名
     private static String password=null;//密码
     private static String driverClass=null;
     //静态代码块中(只加载一次)
     static{
         try {
             //读取db.properties
             Properties props=new Properties();
             InputStream in=JdbcUtil.class.getResourceAsStream("/db.properties");
             //加载文件
             props.load(in);
             url=props.getProperty("url");
             user=props.getProperty("user");
             password=props.getProperty("password");
             driverClass=props.getProperty("driverClass");
             //注册驱动
             Class.forName(driverClass);
         } catch (FileNotFoundException e) {
             e.printStackTrace();
         } catch (IOException e) {
             e.printStackTrace();
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
             System.out.println("注册驱动失败");
         }
     }
     /*
       * 获取连接
       * */
     public static Connection getConnection(){
         try {
             Connection conn=DriverManager.getConnection(url, user, password);
             return conn;
         } catch (SQLException e) {
             e.printStackTrace();
             throw new RuntimeException();
         }
     }
      /*
       * 释放资源
       * */
     public static void close(Connection conn,Statement stmt,ResultSet rs){
         try {
             if(stmt!=null) stmt.close();
             if(conn!=null) conn.close();
             if(rs!=null) rs.close();
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }
 }

Page 实体类

 package com.shore.entity;

 import java.util.List;

 //封装与分页有关的所有信息
 public class Page {
     private List records;//要显示的分页记录
     private int currentPageNum;//当前页码；可由用户指定（用于输入页码，点击跳转到指定页）*
     private int pageSize = 10;//每页显示的记录条数（这里是没页显示10条数据） *
     private int totalPageNum;//总页数*
     private int prePageNum;//上一页的页码*
     private int nextPageNum;//下一页的页码*

     private int startIndex;//数据库每页开始记录的索引（比如第2页是从11开始，第三页从21开始...）*
     private int totalRecords;//总记录的条数*
     //扩展的
     private int startPage;//开始页码
     private int endPage;//结束页码

     private String url;//查询分页的请求servlet的地址

     //currentPageNum：用户要看的页码
     //totalRecords:总记录条数
     public Page(int currentPageNum,int totalRecords){
         this.currentPageNum = currentPageNum;
         this.totalRecords = totalRecords;
         //计算总页数
         totalPageNum = totalRecords%pageSize==0?totalRecords/pageSize:(totalRecords/pageSize+1);
         //计算每页开始的索引
         startIndex = (currentPageNum-1)*pageSize;
         //计算开始和结束页码:9个页码
         if(totalPageNum > 9){
             //超过9页
             startPage = currentPageNum - 4;
             endPage = currentPageNum + 4;
             if(startPage < 1){
                 startPage = 1;
                 endPage = 9;
             }
             if(endPage>totalPageNum){
                 endPage = totalPageNum;
                 startPage = endPage - 8;
             }
         }else{
             //没有9页
             startPage = 1;
             endPage = totalPageNum;
         }
     }
     public List getRecords() {
         return records;
     }
     public void setRecords(List records) {
         this.records = records;
     }
     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 getTotalPageNum() {
         return totalPageNum;
     }
     public void setTotalPageNum(int totalPageNum) {
         this.totalPageNum = totalPageNum;
     }
     //不能无限上一页（假如当前页是第1页，那么“上一页”这个按钮变为灰色，再点击，则 无反应）
     public int getPrePageNum() {
         prePageNum = currentPageNum-1;
         if(prePageNum < 1){
             prePageNum = 1;
         }
         return prePageNum;
     }
     public void setPrePageNum(int prePageNum) {
         this.prePageNum = prePageNum;
     }
     //不能无限下一页（假如当前页是最后一页，那么“下一页”这个按钮变为灰色，再点击，则 无反应）
     public int getNextPageNum() {
         nextPageNum = currentPageNum + 1;
         if(nextPageNum > totalPageNum){
         if(nextPageNum > totalPageNum){
             nextPageNum = totalPageNum;
         }
         return nextPageNum;
     }
     public void setNextPageNum(int nextPageNum) {
         this.nextPageNum = nextPageNum;
     }
     public int getStartIndex() {
         return startIndex;
     }
     public void setStartIndex(int startIndex) {
         this.startIndex = startIndex;
     }
     public int getTotalRecords() {
         return totalRecords;
     }
     public void setTotalRecords(int totalRecords) {
         this.totalRecords = totalRecords;
     }
     public int getStartPage() {
         return startPage;
     }
     public void setStartPage(int startPage) {
         this.startPage = startPage;
     }
     public int getEndPage() {
         return endPage;
     }
     public void setEndPage(int endPage) {
         this.endPage = endPage;
     }
     public String getUrl() {
         return url;
     }
     public void setUrl(String url) {
         this.url = url;
     }
 }

ContactDAOMySqlImpl 实现类

 package com.shore.dao.impl;

 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.util.ArrayList;
 import java.util.List;

 import com.shore.dao.ContactDAO;
 import com.shore.entity.Contact;
 import com.shore.util.JdbcUtil;

 public class ContactDAOMySqlImpl implements ContactDAO{

     //总记录数
     public int getTotalRecordsNum() {
         Connection conn = null;
         PreparedStatement stmt = null;
         ResultSet rs = null;
         try{
             //获取数据库的连接
             conn = JdbcUtil.getConnection();
             //准备sql
             String sql = "select count(*) from contact";
             //执行预编译的sql语句(检查语法)
             stmt = conn.prepareStatement(sql);
             //执行sql语句
             rs = stmt.executeQuery();
             if(rs.next()){//把查到的结果返回给调用者
                 return rs.getInt(1);
             }
             return 0;
         }catch(Exception e){
             throw new RuntimeException(e);
         }finally{//关闭资源
             JdbcUtil.close(conn, stmt, rs);
         }
     }

     //每页的记录数
     public List<Contact> getPageRecords(int startIndex, int offset) {
         Connection conn = null;
         PreparedStatement stmt = null;
         ResultSet rs = null;
         try{
             //获取数据库的连接
             conn = JdbcUtil.getConnection();
             //执行预编译的sql语句(检查语法)
             stmt = conn.prepareStatement("select * from contact limit ?,?");
             //设置参数
             stmt.setInt(1, startIndex);
             stmt.setInt(2, offset);
             //发送参数,执行sql
             rs = stmt.executeQuery();
             List<Contact> cs = new ArrayList<Contact>();
             while(rs.next()){
                 Contact c=new Contact();
                 c.setId(rs.getString("id"));
                 c.setName(rs.getString("name"));
                 c.setSex(rs.getString("sex"));
                 c.setAge(rs.getInt("age"));
                 c.setPhone(rs.getString("phone"));
                 c.setEmail(rs.getString("email"));
                 c.setQq(rs.getString("qq"));
                 cs.add(c);
             }
             return cs;
         }catch(Exception e){
             throw new RuntimeException(e);
         }finally{//关闭资源
             JdbcUtil.close(conn, stmt, rs);
         }
     }
 }

ContactServiceimpl 实现类

 package com.shore.service.impl;

 import java.util.List;

 import com.shore.dao.ContactDAO;
 import com.shore.dao.impl.ContactDAOMySqlImpl;
 import com.shore.entity.Page;
 import com.shore.service.ContactService;

 public class ContactServiceimpl implements ContactService{
     ContactDAO dao=new ContactDAOMySqlImpl();

     public Page findPage(String pageNum) {
         int num = 1;//用户要看的页码,默认是1
         if(pageNum!=null&&!pageNum.trim().equals("")){//解析用户要看的页码
             num = Integer.parseInt(pageNum);
         }
         int totalRecords = dao.getTotalRecordsNum();//得到总记录的条数
         Page page = new Page(num, totalRecords);//对象创建出来后,很多的参数就已经计算完毕
         //查询分页的记录（当前页显示的记录）
         List records = dao.getPageRecords(page.getStartIndex(), page.getPageSize());
         page.setRecords(records);
         return page;
     }
 }

ListContactServlet 类

 package com.shore.servlet;

 import java.io.IOException;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import com.shore.entity.Page;
 import com.shore.service.ContactService;
 import com.shore.service.impl.ContactServiceimpl;

 public class ListContactServlet extends HttpServlet {
     /*
      * 显示所有联系人的逻辑
      * */
     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         ContactService service=new ContactServiceimpl();
         String num=request.getParameter("num");
         Page page=service.findPage(num);
         page.setUrl("/ListContactServlet");
         request.setAttribute("page",page);
         request.getRequestDispatcher("/listContact.jsp").forward(request, response);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         doGet(request, response);
     }
 }

listContact.jsp 查询页面

 <%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
 <%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml">
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
 <title>查询所有联系人</title>
 <style type="text/css">
     table td{
         /*文字居中*/
         text-align:center;
     }

     /*合并表格的边框*/
     table{
         border-collapse:collapse;
     }
 </style>
 </head>

 <body>
 <center><h3>查询所有联系人</h3></center>
 <table align="center" border="1" width="700px">
     <tr>
         <th>编号</th>
         <th>姓名</th>
         <th>性别</th>
         <th>年龄</th>
         <th>电话</th>
         <th>邮箱</th>
         <th>QQ</th>
         <th>操作</th>
     </tr>
     <c:forEach items="${page.records}" var="con" varStatus="varSta">
     <tr>
         <td>${varSta.count }</td>
         <td>${con.name }</td>
         <td>${con.sex }</td>
         <td>${con.age }</td>
         <td>${con.phone }</td>
         <td>${con.email }</td>
         <td>${con.qq }</td>
         <td><a href="${pageContext.request.contextPath }/QueryContactServlet?id=${con.id}">修改</a>&nbsp;<a href="${pageContext.request.contextPath }/DeleteContactServlet?id=${con.id}">删除</a></td>
     </tr>
     </c:forEach>
     <tr>
         <td colspan="8" align="center"><a href="${pageContext.request.contextPath }/addContact.jsp">[添加联系人]</a></td>
     </tr>
 </table>
 <%@include file="/common/page.jsp"%>
 </body>
 </html>

page.jsp 被包含的页面

 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 <!-- 分页显示：开始 -->

       第${page.currentPageNum }页/共${page.totalPageNum }页&nbsp;&nbsp;
       <a href="${pageContext.request.contextPath}/ListContactServlet?num=1">首页</a>
       <a href="${pageContext.request.contextPath}/ListContactServlet?num=${page.prePageNum}">上一页</a>

       <c:forEach begin="${page.startPage}" end="${page.endPage}" var="num">
           <a href="${pageContext.request.contextPath}/ListContactServlet?num=${num}">${num}</a>
       </c:forEach>

       <a href="${pageContext.request.contextPath}/ListContactServlet?num=${page.nextPageNum}">下一页</a>
       <a href="${pageContext.request.contextPath}/ListContactServlet?num=${page.totalPageNum }">尾页</a>

       &nbsp;&nbsp;
       <input type="button" id="bt1" value="跳转到" onclick="jump()"/>&nbsp;<input type="text" size="3" id="num" name="num" />页
       &nbsp;&nbsp;
       <select name="selNum" onchange="jump1(this)">
           <c:forEach begin="1" end="${page.totalPageNum }" var="num">
               <option value="${num}" ${page.currentPageNum==num?'selected="selected"':'' } >${num}</option>
           </c:forEach>
       </select>

       <script type="text/javascript">
           function jump(){
               var numValue = document.getElementById("num").value;
               //验证
               if(!/^[1-9][0-9]*$/.test(numValue)){//验证是否是自然整数
                   alert("请输入正确的页码");
                   return;
               }
               if(numValue>${page.totalPageNum}){
                   alert("页码不能超过最大页数");
                   return;
               }
               window.location.href="${pageContext.request.contextPath}/ListContactServlet?num="+numValue;
           }

           function jump1(selectObj){
               window.location.href="${pageContext.request.contextPath}/ListContactServlet?num="+selectObj.value;
           }
       </script>

       <!-- 分页显示：结束 -->

最终效果图：

原创作者：DSHORE

作者主页：http://www.cnblogs.com/dshore123/

原文出自：https://www.cnblogs.com/dshore123/p/10597898.html

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