JAVA的PageHelper分页 分页javaweb

分页：

分页,是一种将所有数据分段展示的技术，用户每次看到的是通过分页展示的一部分。

通过分页技术的实现，一方面充分利用和学习各种优化工具，并加深对jDBC的理解；另一方面，熟悉web开发的流程。

 

实现思路流程：

0.准备

0.1）在WEB-INF下新建lib文件夹，导入所需的jar文件，并添加到build path 中。

0.2）在src下编辑c3p0-config.xml文件

1.在util包中写JdbcUtils.java和PageBean.java

2.在entity包中写student.java（用了DbUtils组件，属性与数据库保持一致）①实体类设计

3.在dao包中写接口IStudentDao.java ②数据访问层设计

在dao.impl包中写StudentDao.java

4.在service包中写接口IStudentService.java ③业务逻辑层设计

在service.impl包中写StudentService.java

5.在servlet包中写一个servlet：IndexServlet.java ④servlet控制层开发

6.在WEB-INF下写list.jsp ⑤jsp显示数据

最终的包结构：

事先准备的测试数据库，信息如下：

 

0.准备

0.1）在WEB-INF下新建lib文件夹，导入所需的jar文件，并添加到build path 中。

0.2）在src下编辑c3p0-config.xml文件

<c3p0-config>
	<default-config>
		<property name="jdbcUrl">jdbc:mysql://localhost:3306/xiaohua
		</property>
		<property name="driverClass">com.mysql.jdbc.Driver</property>
		<property name="user">root</property>
		<property name="password">root</property>
		<property name="initialPoolSize">3</property>
		<property name="maxPoolSize">6</property>
		<property name="maxIdleTime">1000</property>
	</default-config>
	
	<named-config name="mysql_config">
		<property name="jdbcUrl">jdbc:mysql://localhost:3306/xiaohua</property>
		<property name="driverClass">com.mysql.jdbc.Driver</property>
		<property name="user">root</property>
		<property name="password">root</property>
		<property name="initialPoolSize">3</property>
		<property name="maxPoolSize">6</property>
		<property name="maxIdleTime">1000</property>
	</named-config>
</c3p0-config>

1.在util包中写JdbcUtils.java和PageBean.java

package xiaohua.utils;
import javax.sql.DataSource;

import org.apache.commons.dbutils.QueryRunner;

import com.mchange.v2.c3p0.ComboPooledDataSource;

/**
 * @author xiaohua  
 * 2018-11-12
 * 1.初始化c3p0连接池
 * 2.创建DbUtils核心工具类对象
 */
public class JdbcUtils {
	private static DataSource dataSource;
	static {
		dataSource=new ComboPooledDataSource();
	}
	
	public static QueryRunner getQueryRunner() {
		return new QueryRunner(dataSource);
	}
}

 

 

package xiaohua.utils;

import java.util.List;
//封装分页的参数
public class PageBean <T>{
	private int currentPage=1;//当前页，默认显示第一页
	private int pageCount=5;//查询返回的行数，默认每页显示5行
	private int totalCount;//总记录数
	private int totalPage;//总页数
	private List<T> pageData;//分页查询到的数据
	
	public PageBean() {
		super();
	}
	//返回总页数
	public int getTotalPage() {
		if(totalCount%pageCount==0) {
			totalPage=totalCount/pageCount;
		}else {
			totalPage=totalCount/pageCount+1;
		}
		return totalPage;
	}
	public void setTotalPage(int totalPage) {
		this.totalPage = totalPage;
	}
	public int getCurrentPage() {
		return currentPage;
	}
	public void setCurrentPage(int currentPage) {
		this.currentPage = currentPage;
	}
	public int getPageCount() {
		return pageCount;
	}
	public void setPageCount(int pageCount) {
		this.pageCount = pageCount;
	}
	public int getTotalCount() {
		return totalCount;
	}
	public void setTotalCount(int totalCount) {
		this.totalCount = totalCount;
	}
	public List<T> getPageData() {
		return pageData;
	}
	public void setPageData(List<T> pageData) {
		this.pageData = pageData;
	}
	
}

 

2.在entity包中写student.java（用了DbUtils组件，属性与数据库保持一致）

package xiaohua.entity;
//1.模拟一个实体类：Student
public class Student {
	private int id;
	private String name;
	private	int age;
	
	public Student() {
		super();
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	
}

3.在dao包中写接口IStudentDao.java
 

package xiaohua.dao;

import xiaohua.entity.Student;
import xiaohua.utils.PageBean;

//2.数据访问层设计 之  接口
public interface IStudentDao {
	//分页查询数据
	public void getAll(PageBean<Student> pb);
	//查询总记录数
	public int getTotalCount();
}

 

在dao.impl包中写StudentDao.java

package xiaohua.dao.impl;

import java.util.List;

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;

import xiaohua.dao.IStudentDao;
import xiaohua.entity.Student;
import xiaohua.utils.JdbcUtils;
import xiaohua.utils.PageBean;
//2.数据访问层   实现
public class StudentDao implements IStudentDao {
	@Override
	public void getAll(PageBean<Student> pb) {
		//将查询到的总记录数，设置到pb对象中
		int totalCount =this.getTotalCount();
		pb.setTotalCount(totalCount);
		
		/*
		 * 问题： jsp页面，如果当前页为首页，再点击上一页报错！
		 *            如果当前页为末页，再点下一页显示有问题！
		 * 解决：
		 * 	   1. 如果当前页 <= 0;       设置当前页为1;
		 * 	   2. 如果当前页 > 最大页数；  设置当前页为最大页数
		 */
		if(pb.getCurrentPage()<=0) {
			pb.setCurrentPage(1);
		}else if(pb.getCurrentPage()>pb.getTotalPage()) {
			pb.setCurrentPage(pb.getTotalPage());
		}
		
		//获取当前页，计算当前页的起始行、查询返回的行数
		int currentPage=pb.getCurrentPage();
		int index=(currentPage-1)*pb.getPageCount();
		int count=pb.getPageCount();
		//分页查询数据
		String sql="SELECT * FROM stu LIMIT ?,?";
		try {
			QueryRunner qr=JdbcUtils.getQueryRunner();
			//查询当前页数据，并设置到pb对象中
			List<Student> pageData=qr.query(sql, new BeanListHandler<Student>(Student.class), index,count);
			pb.setPageData(pageData);
			
		}catch(Exception e) {
			throw new RuntimeException(e);
		}
		
	}

	@Override
	public int getTotalCount() {
		//查询总记录数
		String sql="SELECT COUNT(*) FROM stu";
		try {
			QueryRunner qr=JdbcUtils.getQueryRunner();
			Long count=qr.query(sql,new ScalarHandler<Long>());
			return count.intValue();	
		}catch(Exception e) {
			throw new RuntimeException(e);
		}
	}
}

4.在service包中写接口IStudentService.java

package xiaohua.service;

import xiaohua.entity.Student;
import xiaohua.utils.PageBean;

//3.业务逻辑层设计之  接口
public interface IStudentService {
	//分页查询数据
	public void getAll(PageBean<Student> pb);
}

在service.impl包中写StudentService.java

 

package xiaohua.service.impl;

import xiaohua.dao.IStudentDao;
import xiaohua.dao.impl.StudentDao;
import xiaohua.entity.Student;
import xiaohua.service.IStudentService;
import xiaohua.utils.PageBean;
//3. 业务逻辑层    实现
public class StudentService implements IStudentService{
	//创建Dao实例
	private IStudentDao studentDao=new StudentDao();
	@Override
	public void getAll(PageBean<Student> pb) {
		
		try {
			studentDao.getAll(pb);
		}catch(Exception e) {
			throw new RuntimeException(e);
		}
	}
	
}

5.在servlet包中写一个servlet：IndexServlet.java

package xiaohua.servlet;

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 xiaohua.entity.Student;
import xiaohua.service.IStudentService;
import xiaohua.service.impl.StudentService;
import xiaohua.utils.PageBean;
//4.控制层开发

@WebServlet("/IndexServlet")
public class IndexServlet extends HttpServlet {
	// 创建Service实例
	private IStudentService employeeService = new StudentService();
	// 跳转资源
	private String uri;

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
		try {
			//1. 获取“当前页”参数；  (第一次访问当前页为null) 
			String currPage = request.getParameter("currentPage");
			// 判断
			if (currPage == null || "".equals(currPage.trim())){
				currPage = "1";  	// 第一次访问，设置当前页为1;
			}
			// 转换
			int currentPage = Integer.parseInt(currPage);
			
			//2. 创建PageBean对象，设置当前页参数； 传入service方法参数
			PageBean<Student> pageBean = new PageBean<Student>();
			pageBean.setCurrentPage(currentPage);
			
			//3. 调用service  
			employeeService.getAll(pageBean);  // 【pageBean已经被dao填充了数据】
	
			//4. 保存pageBean对象，到request域中
			request.setAttribute("pageBean", pageBean);
			//5. 跳转 
			uri = "/WEB-INF/list.jsp";
		} catch (Exception e) {
			//e.printStackTrace();  // 测试使用
			uri = "/error/error.jsp";
		}
		request.getRequestDispatcher(uri).forward(request, response);
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doGet(request, response);
	}
}

6.在WEB-INF下写list.jsp

 

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!-- 引入jstl核心标签库 -->
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>分页查询数据系统</title>
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->
  </head>
  
  <body>
    <table align="center" border="1" width="80%" cellpadding="5" cellspacing="0">
    	<tr>
    		<td>序号</td>
    		<td>姓名</td>
    		<td>年龄</td>
    	</tr>
    	<!-- 迭代数据 -->
    	<c:choose>
    		<c:when test="${not empty requestScope.pageBean.pageData }">
    			<c:forEach var="stu" items="${requestScope.pageBean.pageData }" varStatus="status" >
    				<tr>
    					<td>${status.count }</td>
    					<td>${stu.name }</td>
    					<td>${stu.age }</td>
    				</tr>
    			
    			</c:forEach>
    		</c:when>
    		<c:otherwise>
    			<tr>
    				<td>对不起，没有你要找的数据</td>
    			</tr>
    		</c:otherwise>
    	</c:choose>
    	<tr>
    		<td  colspan="3" align="center">
    			当前${requestScope.pageBean.currentPage }/${requestScope.pageBean.totalPage }页   
    			<a href="${pageContext.request.contextPath }/IndexServlet?currentPage=1">首页</a>
    			<a href="${pageContext.request.contextPath }/IndexServlet?currentPage=${requestScope.pageBean.currentPage-1}">上一页</a>
    			<a href="${pageContext.request.contextPath }/IndexServlet?currentPage=${requestScope.pageBean.currentPage+1}">下一页</a>
    			<a href="${pageContext.request.contextPath }/IndexServlet?currentPage=${requestScope.pageBean.totalPage}">末页</a>
    		</td>
    	</tr>
    	
    </table>
  </body>
</html>

打开浏览器访问，查看

 

点下一页，没有问题：

 

点末页，没有问题

此时再点下一页，可以看到此时   currentPage=6 

仍显示末页内容