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>

总结

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