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前言：上一讲博客已经基本上开发好了查看客户的功能，但我们并不满足于此，在这一讲博客中，我们将实现分页显示。

数据库分页

分页结构

完成WEB页面的分页显示，需要：

• 先获得需分页显示的记录总数，然后在WEB页面中显示页码；
• 根据页码，从数据库中查询相应的记录显示在WEB页面中。

要实现分页查询，我们一定要弄清楚如下分页设计结构图：

实现客户关系管理系统的分页查询

创建实现分页显示的三个对象

首先在cn.liayun.domain包下创建QueryInfo类，用于封装用户的请求参数。该类的具体代码如下：

package cn.liayun.domain;/** * 封装查询信息的实体 * @author liayun * */public class QueryInfo {
   	private int currentpage = 1;//用户当前看的页	private int pagesize = 5;//记住用户想看的页面大小	private int startindex;//记住用户看的页的数据在数据库的起始位置		public int getCurrentpage() {
   		return currentpage;	}	public void setCurrentpage(int currentpage) {
   		this.currentpage = currentpage;	}	public int getPagesize() {
   		return pagesize;	}	public void setPagesize(int pagesize) {
   		this.pagesize = pagesize;	}	public int getStartindex() {
   		this.startindex = (this.currentpage - 1) * this.pagesize;		return startindex;	}}

然后在cn.liayun.domain包下创建QueryResult类，用于封装查询结果。该类的具体代码如下：

package cn.liayun.domain;import java.util.List;/** * 用来封装查询结果的实体 * @author liayun * */public class QueryResult {
   	private List list;//记住用户看的页的数据	private int totalrecord;//记住总记录数		public List getList() {
   		return list;	}	public void setList(List list) {
   		this.list = list;	}	public int getTotalrecord() {
   		return totalrecord;	}	public void setTotalrecord(int totalrecord) {
   		this.totalrecord = totalrecord;	}}

最后，在cn.liayun.domain包下创建PageBean类。该类用于将QueryResult对象中封装的查询结果，生成显示分页数据的PageBean对象。

package cn.liayun.domain;import java.util.List;/** * 封装页面显示需要的信息 * @author liayun * */public class PageBean {
   	private List list;	private int totalrecord;	private int pagesize;	private int totalpage;	private int currentpage;	private int previouspage;	private int nextpage;	private int[] pagebar;		public List getList() {
   		return list;	}	public void setList(List list) {
   		this.list = list;	}	public int getTotalrecord() {
   		return totalrecord;	}	public void setTotalrecord(int totalrecord) {
   		this.totalrecord = totalrecord;	}	public int getPagesize() {
   		return pagesize;	}	public void setPagesize(int pagesize) {
   		this.pagesize = pagesize;	}	public int getTotalpage() {
   		//根据总记录数和页面大小算出来的		//100	5	20		//101	5	21		//99	5	20		if (this.totalrecord % this.pagesize == 0) {
   			this.totalpage = this.totalrecord / this.pagesize;		} else {
   			this.totalpage = this.totalrecord / this.pagesize + 1;		}		return totalpage;	}		public int getCurrentpage() {
   		return currentpage;	}	public void setCurrentpage(int currentpage) {
   		this.currentpage = currentpage;	}	public int getPreviouspage() {
   		if (this.currentpage - 1 < 1) {
   			this.previouspage = 1;		} else {
   			this.previouspage = this.currentpage - 1;		}				return previouspage;	}	public int getNextpage() {
   		if (this.currentpage + 1 >= this.totalpage) {
   			this.nextpage = this.totalpage;		} else {
   			this.nextpage = this.currentpage + 1;		}		return nextpage;	}	public int[] getPagebar() {
   		/*		int[] pagebar = new int[this.totalpage];		for (int i = 1; i <= this.totalpage; i++) {			pagebar[i - 1] = i;		}		this.pagebar = pagebar;		return pagebar;		*/				int startpage;//起始页码		int endpage;//结束页码		int[] pagebar = null;		if (this.totalpage <= 10) {
   			pagebar = new int[this.totalpage];			startpage = 1;			endpage = this.totalpage;		} else {
   			pagebar = new int[10];			startpage = this.currentpage - 4;			endpage = this.currentpage + 5;						//总页数=30		3		-1			//总页数=30		29		34			// 总页数=30，假设看的是第3页，则startpage=-1            // 总页数=30，假设看的是第29页，则endpage=34			if (startpage < 1) {
   				startpage = 1;				endpage = 10;			}						if (endpage > this.totalpage) {
   				endpage = this.totalpage;				startpage = this.totalpage - 9;			}		}				int index = 0;		for (int i = startpage; i <= endpage; i++) {
   			pagebar[index++] = i;		}		this.pagebar = pagebar;		return this.pagebar;	}}

修改数据访问层(dao、dao.impl)

首先，将CustomerDao接口的代码修改为：

package cn.liayun.dao;import java.util.List;import cn.liayun.domain.Customer;import cn.liayun.domain.QueryResult;public interface CustomerDao {
   	void add(Customer c);	void update(Customer c);	void delete(String id);	Customer find(String id);	List
   
     getAll();		//获取到页面数据和页面大小	public QueryResult pageQuery(int startindex, int pagesize);}
   

然后修改CustomerDao接口的CustomerDaoImpl实现类的代码为：

package cn.liayun.dao.impl;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.util.ArrayList;import java.util.List;import cn.liayun.dao.CustomerDao;import cn.liayun.domain.Customer;import cn.liayun.domain.QueryResult;import cn.liayun.exception.DaoException;import cn.liayun.utils.JdbcUtils;public class CustomerDaoImpl implements CustomerDao {
   		@Override	public void add(Customer c) {
   		Connection conn = null;		PreparedStatement st = null;		ResultSet rs = null;				try {
   			conn = JdbcUtils.getConnection();			String sql = "insert into customer(id,name,gender,birthday,cellphone,email,preference,type,description) values(?,?,?,?,?,?,?,?,?)";			st = conn.prepareStatement(sql);			st.setString(1, c.getId());			st.setString(2, c.getName());			st.setString(3, c.getGender());			st.setDate(4, new java.sql.Date(c.getBirthday().getTime()));			st.setString(5, c.getCellphone());			st.setString(6, c.getEmail());			st.setString(7, c.getPreference());			st.setString(8, c.getType());			st.setString(9, c.getDescription());						st.executeUpdate();		} catch (Exception e) {
   			throw new DaoException(e);		} finally {
   			JdbcUtils.release(conn, st, rs);		}	}		@Override	public void update(Customer c) {
   		Connection conn = null;		PreparedStatement st = null;		ResultSet rs = null;				try {
   			conn = JdbcUtils.getConnection();			String sql = "update customer set name=?,gender=?,birthday=?,cellphone=?,email=?,preference=?,type=?,description=? where id=?";			st = conn.prepareStatement(sql);			st.setString(1, c.getName());			st.setString(2, c.getGender());			st.setDate(3, new java.sql.Date(c.getBirthday().getTime()));			st.setString(4, c.getCellphone());			st.setString(5, c.getEmail());			st.setString(6, c.getPreference());			st.setString(7, c.getType());			st.setString(8, c.getDescription());			st.setString(9, c.getId());			st.executeUpdate();		} catch (Exception e) {
   			throw new DaoException(e);		} finally {
   			JdbcUtils.release(conn, st, rs);		}	}		@Override	public void delete(String id) {
   		Connection conn = null;		PreparedStatement st = null;		ResultSet rs = null;				try {
   			conn = JdbcUtils.getConnection();			String sql = "delete from customer where id=?";			st = conn.prepareStatement(sql);			st.setString(1, id);			st.executeUpdate();		} catch (Exception e) {
   			throw new DaoException(e);		} finally {
   			JdbcUtils.release(conn, st, rs);		}	}		@Override	public Customer find(String id) {
   		Connection conn = null;		PreparedStatement st = null;		ResultSet rs = null;				try {
   			conn = JdbcUtils.getConnection();			String sql = "select * from customer where id=?";			st = conn.prepareStatement(sql);			st.setString(1, id);			rs = st.executeQuery();			if (rs.next()) {
   				Customer c = new Customer();				c.setBirthday(rs.getDate("birthday"));				c.setCellphone(rs.getString("cellphone"));				c.setDescription(rs.getString("description"));				c.setEmail(rs.getString("email"));				c.setGender(rs.getString("gender"));				c.setId(rs.getString("id"));				c.setName(rs.getString("name"));				c.setPreference(rs.getString("preference"));				c.setType(rs.getString("type"));				return c;			}			return null;		} catch (Exception e) {
   			throw new DaoException(e);		} finally {
   			JdbcUtils.release(conn, st, rs);		}	}		@Override	public List
   
     getAll() {
   		Connection conn = null;		PreparedStatement st = null;		ResultSet rs = null;				try {
   			conn = JdbcUtils.getConnection();			String sql = "select * from customer";			st = conn.prepareStatement(sql);			rs = st.executeQuery();			List
    
      list = new ArrayList
     
      ();			while (rs.next()) {
   				Customer c = new Customer();				c.setBirthday(rs.getDate("birthday"));				c.setCellphone(rs.getString("cellphone"));				c.setDescription(rs.getString("description"));				c.setEmail(rs.getString("email"));				c.setGender(rs.getString("gender"));				c.setId(rs.getString("id"));				c.setName(rs.getString("name"));				c.setPreference(rs.getString("preference"));				c.setType(rs.getString("type"));				list.add(c);			}			return list;		} catch (Exception e) {
   			throw new DaoException(e);		} finally {
   			JdbcUtils.release(conn, st, rs);		}	}		//获取到页面数据以及总记录数	public QueryResult pageQuery(int startindex, int pagesize) {
   		Connection conn = null;		PreparedStatement st = null;		ResultSet rs = null;				QueryResult qr = new QueryResult();		try {
   			conn = JdbcUtils.getConnection();			String sql = "select * from customer limit ?,?";			st = conn.prepareStatement(sql);			st.setInt(1, startindex);			st.setInt(2, pagesize);			rs = st.executeQuery();			List
      
        list = new ArrayList
       
        ();			while (rs.next()) {
   				Customer c = new Customer();				c.setBirthday(rs.getDate("birthday"));				c.setCellphone(rs.getString("cellphone"));				c.setDescription(rs.getString("description"));				c.setEmail(rs.getString("email"));				c.setGender(rs.getString("gender"));				c.setId(rs.getString("id"));				c.setName(rs.getString("name"));				c.setPreference(rs.getString("preference"));				c.setType(rs.getString("type"));				list.add(c);			}			qr.setList(list);						// 还要进行一次查询，查询出总记录数			sql = "select count(*) from customer";			st = conn.prepareStatement(sql);			rs = st.executeQuery();			if (rs.next()) {
   				qr.setTotalrecord(rs.getInt(1));			}			return qr;		} catch (Exception e) {
   			throw new DaoException(e);		} finally {
   			JdbcUtils.release(conn, st, rs);		}	}	}
       
      
     
    
   

修改service层(service层对web层提供所有的业务服务)

首先，修改BusinessService接口的代码为：

package cn.liayun.service;import java.util.List;import cn.liayun.domain.Customer;import cn.liayun.domain.PageBean;import cn.liayun.domain.QueryInfo;//业务类，统一对Web层提供所有服务public interface BusinessService {
   	void addCustomer(Customer c);	void updateCustomer(Customer c);	void deleteCustomer(String id);	Customer findCustomer(String id);	List
   
     getAllCustomer();		public PageBean pageQuery(QueryInfo queryInfo);}
   

然后修改BusinessService接口的BusinessServiceImpl实现类的代码为：

package cn.liayun.service.impl;import java.util.List;import cn.liayun.dao.CustomerDao;import cn.liayun.dao.impl.CustomerDaoImpl;import cn.liayun.domain.Customer;import cn.liayun.domain.PageBean;import cn.liayun.domain.QueryInfo;import cn.liayun.domain.QueryResult;import cn.liayun.service.BusinessService;//此业务层代码很少，所以称为薄薄的业务层public class BusinessServiceImpl implements BusinessService {
   	private CustomerDao dao = new CustomerDaoImpl();		@Override	public void addCustomer(Customer c) {
   		dao.add(c);	}		@Override	public void updateCustomer(Customer c) {
   		dao.update(c);	}		@Override	public void deleteCustomer(String id) {
   		dao.delete(id);	}		@Override	public Customer findCustomer(String id) {
   		return dao.find(id);	}		@Override	public List
   
     getAllCustomer() {
   		return dao.getAll();	}		public PageBean pageQuery(QueryInfo queryInfo) {
   		//调用Dao获取到页面数据		QueryResult qr = dao.pageQuery(queryInfo.getStartindex(), queryInfo.getPagesize());				//根据Dao的查询结果，生成页面显示需要的PageBean		PageBean bean = new PageBean();		bean.setCurrentpage(queryInfo.getCurrentpage());		bean.setList(qr.getList());		bean.setPagesize(queryInfo.getPagesize());		bean.setTotalrecord(qr.getTotalrecord());		return bean;	}}
   

修改web层

修改ListCustomerServlet，用于处理用户分页查询请求。ListCustomerServlet的具体代码如下：

package cn.liayun.web.controller;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 cn.liayun.domain.PageBean;import cn.liayun.domain.QueryInfo;import cn.liayun.service.BusinessService;import cn.liayun.service.impl.BusinessServiceImpl;import cn.liayun.utils.WebUtils;//处理用户的分页请求@WebServlet("/ListCustomerServlet")public class ListCustomerServlet extends HttpServlet {
   		protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
   			try {
   			/*             * 如果用户带查询条件过来，就将查询条件封装到QueryInfo里面去。             * 如果用户没有带查询条件过来，也即第一次查询，也要生成一个QueryInfo，使用默认查询条件，即从第1页查看5条记录。             */			QueryInfo info = WebUtils.request2Bean(request, QueryInfo.class);			BusinessService service = new BusinessServiceImpl();			PageBean pagebean = service.pageQuery(info);			request.setAttribute("pagebean", pagebean);			request.getRequestDispatcher("/WEB-INF/jsp/listcustomer.jsp").forward(request, response);		} catch (Exception e) {
   			// TODO: handle exception			e.printStackTrace();			request.setAttribute("message", "查看用户失败！！！");			request.getRequestDispatcher("message.jsp").forward(request, response);		}			}	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
   		doGet(request, response);	}}

接下来就要修改客户显示界面(listcustomer.jsp)了，分页显示这一块，有很多细节需要我们注意，比如：

• 当我们浏览第一页的数据时，上一页超链接就不能显示出来；当我们浏览尾页的数据时，下一页超链接也不能显示出来；
• 当我们浏览到某一页时，页码条中的这一页就应该显示为普通文字，而不是超链接，即该页是无法点击再次查看的；
• 除了点击上一页和下一页，我们还应可自由跳转到任何页面；
• 我们还应可自由控制每页可显示的记录数。

下面我们就按照以上细节来修改客户显示界面(listcustomer.jsp)，修改后的listcustomer.jsp页面代码为：

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"%><%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %><%@ taglib uri="/liayun" prefix="liayun" %>
   	
   			
   
   
		    
     
			      
客户姓名
			      
性别
			      
生日
			      
手机
			      
邮箱
			      
爱好
 			      
类型
 			      
备注
			      
操作
		     
				     
				      
${c.name }
				      
${c.gender }
				      
${c.birthday }
				      
${c.cellphone }
				      
${c.email }
				      
${liayun:sub(c.preference) }
				      
${c.type }
				      
${liayun:sub(c.description) }
				      
					修改					删除				
			     
					    
   
	
					共[${pagebean.totalrecord }]条记录，	每页条，	共[${pagebean.totalpage }]页，	当前第[${pagebean.currentpage }]页，	   	
   		
    上一页	
   		
   		
    			
     ${pagenum }		
    		
    			
     ${pagenum }		
    	
   		
   		
    下一页	
   		

至此，客户关系管理系统的分页查询就完成了，测试结果如下：

转载地址：https://liayun.blog.csdn.net/article/details/52300613 如侵犯您的版权，请留言回复原文章的地址，我们会给您删除此文章，给您带来不便请您谅解！