JavaWeb入门教程之分页查询功能的简单实现

一、MySql实现分页查询的SQL语句

1、分页需求：

客户端通过传递pageNo(页码)，counter(每页显示的条数)两个参数去分页查询数据库表中的数据，那我们知道MySql数据库提供了分页的函数limit m,n，但是该函数的用法和我们的需求不一样，所以就需要我们根据实际情况去改写适合我们自己的分页语句，具体的分析如下：

比如：

查询第1条到第10条的数据的sql是：select * from table limit 0,10;   ->对应我们的需求就是查询第一页的数据：select * from table limit (1-1)*10,10;

查询第10条到第20条的数据的sql是：select * from table limit 10,20;  ->对应我们的需求就是查询第二页的数据：select * from table limit (2-1)*10,10;

查询第20条到第30条的数据的sql是：select * from table limit 20,30;  ->对应我们的需求就是查询第三页的数据：select * from table limit (3-1)*10,10;

2、总结

通过上面的分析，可以得出符合我们自己需求的分页sql格式是：select * from table limit (pageNo-1)*counter,counter; 其中pageNo是页码，counter是每页显示的条数。

二、JavaWeb程序

1、创建PageBeanUtils.java工具类

package com.ambow.utils;
import java.util.List;
public class PageBeanUtils<T> {
private int prePage;//上一页
private int nextPage;//下一页
private int firstPage=1;//首页
private int lastPage;//尾页
private int currentPage = 1;//当前
private int totalPage;//总页数
private int pageSize;//每页显示条数，默认显示10条
private int totalData;//数据总条数
private List<T> pageData;//数据
public PageBeanUtils(int currentPage,int pageSize, int totalData) {
this.currentPage = currentPage;
this.pageSize = pageSize;
this.totalData = totalData;

//计算获得总页数（尾页）
// this.totalPage = this.lastPage = (totalData+pageSize-1)/pageSize;
this.totalPage = this.lastPage = (int)Math.ceil((double)totalData/pageSize);
//防止当前页小于1
this.currentPage = Math.max(this.currentPage, 1);
//防止当前页大于总的页数
this.currentPage = Math.min(this.totalPage, this.currentPage);
//设置上一页，上一页不能小于1
this.prePage = Math.max(this.currentPage-1, 1);
//设置下一页，下一页不能大于总页数
this.nextPage = Math.min(this.currentPage+1, this.totalPage);

/**
* ceil
public static double ceil(double a)
返回最小的（最接近负无穷大） double 值，该值大于等于参数，并等于某个整数。特殊情况如下：
如果参数值已经等于某个整数，那么结果与该参数相同。
如果参数为 NaN、无穷大、正 0 或负 0，那么结果与参数相同。
如果参数值小于 0，但是大于 -1.0，那么结果为负 0。
注意， Math.ceil(x) 的值与 -Math.floor(-x) 的值完全相同。
参数：
a - 一个值。
返回：
最小（最接近负无穷大）浮点值，该值大于等于该参数，并等于某个整数。
*/

}

public PageBeanUtils(int prePage, int nextPage, int firstPage, int lastPage, int currentPage, int totalPage,
int pageSize, int totalData, List<T> pageData) {
super();
this.prePage = prePage;
this.nextPage = nextPage;
this.firstPage = firstPage;
this.lastPage = lastPage;
this.currentPage = currentPage;
this.totalPage = totalPage;
this.pageSize = pageSize;
this.totalData = totalData;
this.pageData = pageData;
}
public int getPrePage() {
return prePage;
}
public void setPrePage(int prePage) {
this.prePage = prePage;
}
public int getNextPage() {
return nextPage;
}
public void setNextPage(int nextPage) {
this.nextPage = nextPage;
}
public int getFirstPage() {
return firstPage;
}
public void setFirstPage(int firstPage) {
this.firstPage = firstPage;
}
public int getLastPage() {
return lastPage;
}
public void setLastPage(int lastPage) {
this.lastPage = lastPage;
}
public int getCurrentPage() {
return currentPage;
}
public void setCurrentPage(int currentPage) {
this.currentPage = currentPage;
}
public int getTotalPage() {
return totalPage;
}
public void setTotalPage(int totalPage) {
this.totalPage = totalPage;
}
public int getPageSize() {
return pageSize;
}
public void setPageSize(int pageSize) {
this.pageSize = pageSize;
}
public int getTotalData() {
return totalData;
}
public void setTotalData(int totalData) {
this.totalData = totalData;
}
public List<T> getPageData() {
return pageData;
}
public void setPageData(List<T> pageData) {
this.pageData = pageData;
}

/*
*
*
* totalPage = (totalData+pageSize-1)/pageSize;
*
*
* */
}

2、在接口里面定义分页查询的方法

package com.ambow.dao;

import java.util.List;

import com.ambow.pojo.Good;

public interface IGoodDao {
//增删改查
public void add(Good good);
public void delete(Good good);
public void update(Good good);
public void query(Good good);
public Good queryOne(Good good);
public List<Good> queryMore(Good good);
public List<Good> queryByName(String name);//根据商家名称进行模糊查询
//条件分页查询
public List<Good> queryByName(String name,int currentPage,int pageSize);
//获取满足某个条件的总记录数
public int getTotalNum(String name);
}

3、在接口的实现类里面实现方法

package com.ambow.dao.impl;

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

import com.ambow.dao.IGoodDao;
import com.ambow.pojo.Good;
import com.ambow.utils.DBUtils;

public class GoodDaoImpl implements IGoodDao {
DBUtils db = new DBUtils();
@Override
public void add(Good good) {
Connection conn = null;
PreparedStatement pstmt = null;
String sql = "insert into good (name,address,tel,dishes) values (?,?,?,?)";
try {
conn = DBUtils.getConnection();
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, good.getName());
pstmt.setString(2, good.getAddress());
pstmt.setString(3, good.getTel());
pstmt.setString(4, good.getDishes());
int isOk = pstmt.executeUpdate();
//System.out.println("add-----"+isOk);
} catch (SQLException e) {
e.printStackTrace();
}
}

@Override
public void delete(Good good) {
Connection conn = null;
PreparedStatement pstmt = null;
String sql = "delete from good where id = ?";
try {
conn = DBUtils.getConnection();
pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, good.getId());
int isOk = pstmt.executeUpdate();
System.out.println("delete-----"+isOk);
} catch (SQLException e) {
e.printStackTrace();
}

}

@Override
public void update(Good good) {
Connection conn = null;
PreparedStatement pstmt = null;
String sql = "update good set name=?,address=?,tel=?,dishes=? where id=?";
try {
conn = DBUtils.getConnection();
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, good.getName());
pstmt.setString(2, good.getAddress());
pstmt.setString(3, good.getTel());
pstmt.setString(4, good.getDishes());
pstmt.setInt(5,good.getId());
int isOk = pstmt.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
}

}

@Override
public void query(Good good) {
// TODO Auto-generated method stub

}

@Override
public Good queryOne(Good good) {
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
String sql = "select * from good where id = ?";
Good gd = null;
try {
conn = DBUtils.getConnection();
pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, good.getId());
rs = pstmt.executeQuery();
while(rs.next()){
 gd = new Good(rs.getInt(1),rs.getString(2),rs.getString(3),
 rs.getString(4),rs.getString(5));
}
} catch (SQLException e) {
e.printStackTrace();
}
return gd;

}

@Override
public List<Good> queryMore(Good good) {
// TODO Auto-generated method stub
return null;
}

@Override
public List<Good> queryByName(String name) {
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
String sql = "select * from good where name like ?";
List<Good> goodList = new ArrayList<Good>();
try {
conn = DBUtils.getConnection();
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, "％"+name+"％");
rs = pstmt.executeQuery();
while(rs.next()){
 goodList.add(new Good(rs.getInt(1),rs.getString(2),rs.getString(3),
 rs.getString(4),rs.getString(5)));
}
} catch (SQLException e) {
e.printStackTrace();
}
return goodList;
}

@Override
public List<Good> queryByName(String name, int currentPage, int pageSize) {
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
String sql = "select * from good where name like ? limit ?,?";
List<Good> goodList = new ArrayList<Good>();
try {
conn = DBUtils.getConnection();
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, "％"+name+"％");
pstmt.setInt(2,(currentPage-1)*pageSize);
pstmt.setInt(3,pageSize);
rs = pstmt.executeQuery();
while(rs.next()){
 goodList.add(new Good(rs.getInt(1),rs.getString(2),rs.getString(3),
 rs.getString(4),rs.getString(5)));
}
} catch (SQLException e) {
e.printStackTrace();
}
return goodList;

}

@Override
public int getTotalNum(String name) {
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
String sql = "select count(id) from good where name like ?";
int total = 0;
try {
conn = DBUtils.getConnection();
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, "％"+name+"％");
rs = pstmt.executeQuery();
while(rs.next()){
 total = rs.getInt(1);
}
} catch (SQLException e) {
e.printStackTrace();
}
return total;

}

}

4.在Servlet里面调用实现类里面的分页查询方法

package com.ambow.servlet;

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.ambow.dao.IGoodDao;
import com.ambow.dao.impl.GoodDaoImpl;
import com.ambow.pojo.Good;
import com.ambow.utils.PageBeanUtils;

@WebServlet("/QueryServlet")
public class QueryServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private IGoodDao goodDao = new GoodDaoImpl();
public QueryServlet() {
 super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request,response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("utf-8");
String keywords = request.getParameter("kw");
String method = request.getParameter("method");
if("add".equals(method)){
String name = request.getParameter("name");
String address = request.getParameter("address");
String tel = request.getParameter("tel");
String dishes = request.getParameter("dishes");
Good good = new Good(0,name,address,tel,dishes);
goodDao.add(good);
//调用dao的查询方法，返回一个List
List<Good> goods = goodDao.queryByName(keywords);
request.setAttribute("list", goods);
request.getRequestDispatcher("goods.jsp").forward(request, response);
}else if("search".equals(method)){
if(null==keywords) {
keywords="";
}
int currentPage = 1;
try {
currentPage=Integer.parseInt(request.getParameter("curPage"));
if(currentPage<=0) {
 currentPage = 1;
}
}catch(Exception e) {
currentPage = 1;
}
int pageSize=10;
int totalData = goodDao.getTotalNum(keywords);
int totalPage = (int)Math.ceil((double)totalData/pageSize);
if(currentPage>totalPage){
currentPage = totalPage;
}
List<Good> goods = goodDao.queryByName(keywords,currentPage,pageSize);
PageBeanUtils pg = new PageBeanUtils(currentPage,pageSize,totalData);
pg.setPageData(goods);
request.setAttribute("pg", pg);
request.getRequestDispatcher("good2.jsp").forward(request, response);
}else if("delete".equals(method)){
System.out.println(keywords);
//实现删除
String id = request.getParameter("id");
Good good = new Good();
good.setId(Integer.valueOf(id));
goodDao.delete(good);
//调用dao的查询方法，返回一个List
List<Good> goods = goodDao.queryByName(keywords);
request.setAttribute("list", goods);
request.getRequestDispatcher("goods.jsp").forward(request, response);
}else if("queryById".equals(method)){
//查询一个
String id = request.getParameter("id");
Good good = new Good();
good.setId(Integer.valueOf(id));
good = goodDao.queryOne(good);
//调用dao的查询方法，返回一个good
request.setAttribute("good", good);
request.getRequestDispatcher("update.jsp").forward(request, response);
}else if("update".equals(method)){
String id = request.getParameter("id");
String name = request.getParameter("name");
String address = request.getParameter("address");
String tel = request.getParameter("tel");
String dishes = request.getParameter("dishes");
Good good = new Good(Integer.valueOf(id),name,address,tel,dishes);
goodDao.update(good);
//调用dao的查询方法，返回一个List
List<Good> goods = goodDao.queryByName(keywords);
request.setAttribute("list", goods);
request.getRequestDispatcher("goods.jsp").forward(request, response);
}else{
//调用dao的查询方法，返回一个List
List<Good> goods = goodDao.queryByName(keywords);
request.setAttribute("list", goods);
request.getRequestDispatcher("goods.jsp").forward(request, response);
}
}

}

5.在JSP页面获取Servlet里面传过来的数据

<％@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8" import="java.util.ArrayList,com.ambow.pojo.Good,
com.ambow.pojo.User,com.ambow.utils.PageBeanUtils"％>
<％@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" ％>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>外卖系统的搜索功能</title>
</head>
<body>
<form action="QueryServlet?method=search" method="POST">
<input type="text" name="kw"/><input type="submit" value="搜索"/><a href=" ">添加商家</a >
<table border="1">
<tr><th>商家店名</th><th>商家地址</th><th>商家电话</th><th>经营菜品</th><th colspan="2">编辑</th></tr>
<c:forEach items="${pg.pageData}" var="g">
 <tr><td>${g.name}</td><td>${g.address}</td><td>${g.tel}</td><td>${g.dishes}</td>
 <td><a href="QueryServlet?method=queryById&id=${g.id}">修改</a ></td>
 <td><a href="QueryServlet?method=delete&id=${g.id}" onClick="return confirm('确认删除本条数据吗？');">删除</a ></td></tr>

</c:forEach>
</table>
<a href="QueryServlet?method=search&curPage=${pg.firstPage}">首页</a >
<a href="QueryServlet?method=search&curPage=${pg.currentPage - 1}">上一页</a >
<a href="QueryServlet?method=search&curPage=${pg.currentPage + 1}">下一页</a >
<a href="QueryServlet?method=search&curPage=${pg.lastPage}">尾页</a >
当前第${pg.currentPage}页/共${pg.totalPage}页
每页显示${pg.pageSize}条
</form>

</body>
</html>

来源：https://blog.csdn.net/kuailexiaohan/article/details/109845618