分页

分页的使用非常普遍，现在一步步的把分页功能实现出来，先看看已经写好的效果：

该页面的所有数据都存放在一个javaBean对象(PageBean)里，每次访问该页面时，Serlvet就会把pageBean传到该页面。

model模型

首先需要创建一个PageBean类，里面封装了所有的分页信息，页面上显示的就是pageBean里的值。

其中pageSize、currentPage是自己设置的，其余的属性都由计算得到。

pageBean:

package com.kindleheart.model;

import java.util.List;

public class PageBean<T> {

    private List<T> pageList;//分页的记录信息

    private int pageSize;//页面大小

    private int rowCount;//总记录数

    private int pageCount;//总页面数

    private int currentPage;//当前页面

    private int previousPage;//前一页的页数

    private int nextPage;//后一页的页数

    private int rowStart;//记录起始处

    private int startPage;//开始页码

    private int endPage;//结束页码

    public PageBean(int currentPage, int rowCount, int pageSize) {

        this.currentPage = currentPage;

        this.rowCount = rowCount;

        this.pageSize = pageSize;

        //总页面数

        pageCount = (rowCount+pageSize-1)/pageSize;

        //记录起始处

        rowStart = (currentPage-1)*pageSize;

        startPage = currentPage - 2;

        endPage = currentPage + 2;

        if(pageCount > 5) {

            if(startPage < 1) {

                startPage = 1;

                endPage = startPage + 4;

            }

            if(endPage > pageCount) {

                endPage = rowCount;

                startPage = endPage - 4;

            }

        } else {

            startPage = 1;

            endPage = pageCount;

        }

    }

    public List<T> getPageList() {

        return pageList;

    }

    public void setPageList(List<T> pageList) {

        this.pageList = pageList;

    }

    public int getPageSize() {

        return pageSize;

    }

    public void setPageSize(int pageSize) {

        this.pageSize = pageSize;

    }

    public int getRowCount() {

        return rowCount;

    }

    public void setRowCount(int rowCount) {

        this.rowCount = rowCount;

    }

    public int getPageCount() {

        return pageCount;

    }

    public void setPageCount(int pageCount) {

        this.pageCount = pageCount;

    }

    public int getCurrentPage() {

        return currentPage;

    }

    public void setCurrentPage(int currentPage) {

        this.currentPage = currentPage;

    }

    public int getPreviousPage() {

        previousPage = currentPage - 1;

        if(previousPage < 1) previousPage = 1;

        return previousPage;

    }

    public void setPreviousPage(int previousPage) {

        this.previousPage = previousPage;

    }

    public int getNextPage() {

        nextPage = currentPage + 1;

        if(nextPage > pageCount) nextPage = pageCount;

        return nextPage;

    }

    public void setNextPage(int nextPage) {

        this.nextPage = nextPage;

    }

    public int getRowStart() {

        return rowStart;

    }

    public void setRowStart(int rowStart) {

        this.rowStart = rowStart;

    }

    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;

    }

}

还需要创建一个存储分页的记录信息的model类，也就是Student类。

package com.kindleheart.model;

public class Student {

    private int id;

    private String scold;

    private String name;

    private String sex;

    public Student(int id, String scold, String name, String sex) {

        this.id = id;

        this.scold = scold;

        this.name = name;

        this.sex = sex;

    }

    public Student() {

    }

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getScold() {

        return scold;

    }

    public void setScold(String scold) {

        this.scold = scold;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public String getSex() {

        return sex;

    }

    public void setSex(String sex) {

        this.sex = sex;

    }

}

servlet控制层

在Servlet中有三个任务：

• 获取从网页传来的currentPage(当前页面)　　
• 把pageSize、currentPage传入到service层里的方法中，从service层获取封装好所有数据的PageBean对象
• 把得到的PageBean对象放到request域里

package com.kindleheart.servlet;

import com.kindleheart.model.PageBean;

import com.kindleheart.service.StudentService;

import com.kindleheart.service.impl.StudentServiceImpl;

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 java.io.IOException;

import java.sql.SQLException;

@WebServlet(name = "StudentServlet", urlPatterns = "/student.do")

public class StudentServlet extends HttpServlet {

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        request.setCharacterEncoding("utf-8");

        response.setContentType("text/html;charset=utf-8");

        //得到当前页面

        int currentPage = Integer.parseInt(request.getParameter("currentPage"));

        //得到封装好所有数据的PageBean对象

        StudentService studentService = new StudentServiceImpl();

        PageBean pageBean = null;

        try {

            pageBean = studentService.getStudentsWithPage(currentPage, 3);

        } catch (SQLException e) {

            e.printStackTrace();

        }

        //把pageBean对象放到request域里

        request.setAttribute("pageBean", pageBean);

        request.getRequestDispatcher("jsp/stulist.jsp").forward(request, response);

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        doPost(request, response);

    }

}

service业务逻辑层

在service层里只有一个任务，就是返回封装好所有信息的PageBean对象到Servlet中。

StudentService：

package com.kindleheart.service;

import com.kindleheart.model.PageBean;

import java.sql.SQLException;

public interface StudentService {

    PageBean getStudentsWithPage(int currentPage, int pageSize) throws SQLException;

}

StudentServiceImpl：

package com.kindleheart.service.impl;

import com.kindleheart.dao.StudentDao;

import com.kindleheart.dao.impl.StudentDaoImpl;

import com.kindleheart.model.PageBean;

import com.kindleheart.model.Student;

import com.kindleheart.service.StudentService;

import java.sql.SQLException;

import java.util.List;

public class StudentServiceImpl implements StudentService {

    private StudentDao studentDao = new StudentDaoImpl();

    @Override

    public PageBean getStudentsWithPage(int currentPage, int pageSize) throws SQLException {

        //得到总记录数

        int rowCount = studentDao.getRowCount();

        //创建pageBean对象，并传入值

        PageBean pageBean = new PageBean(currentPage, rowCount, pageSize);

        //把查到的分页信息传入到pageBean中

        List<Student> list = studentDao.getStudentsWithPage(pageBean.getRowStart(), pageSize);

        pageBean.setPageList(list);

        return pageBean;

    }

}

dao数据访问层

在dao层里有两个任务：

• 得到总记录数

• 得到分页的记录信息

StudentDao：

package com.kindleheart.dao;

import com.kindleheart.model.Student;

import java.sql.SQLException;

import java.util.List;

public interface StudentDao {

    int getRowCount() throws SQLException;

    List<Student> getStudentsWithPage(int rowStart, int pageSize) throws SQLException;

}

StudentDaoImpl：

package com.kindleheart.dao.impl;

import com.kindleheart.dao.StudentDao;

import com.kindleheart.model.Student;

import com.kindleheart.utils.JDBCUtil;

import org.apache.commons.dbutils.QueryRunner;

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

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

import java.sql.SQLException;

import java.util.List;

public class StudentDaoImpl implements StudentDao {

    @Override

    public int getRowCount() throws SQLException {

        QueryRunner queryRunner = new QueryRunner(JDBCUtil.getDataSource());

        String sql = "select count(*) from stuifo";

        Object obj = queryRunner.query(sql, new ScalarHandler<>());

        Long num = (Long)obj;

        return num.intValue();

    }

    @Override

    public List<Student> getStudentsWithPage(int rowStart, int pageSize) throws SQLException {

        QueryRunner queryRunner = new QueryRunner(JDBCUtil.getDataSource());

        String sql = "select * from stuifo limit ?,?";

        return queryRunner.query(sql, new BeanListHandler<>(Student.class), rowStart, pageSize);

    }

}

JSP页面

在JSP页面显示所有的分页信息。

stulist：

<%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %>

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<%

    String path = request.getContextPath();

    String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<html>

<head>

    <title>stulist</title>

    <base href="<%=basePath%>"/>

</head>

<body>

<div>

    <p id="p">学生信息</p>

    <table border="1px" width="500px">

        <tr>

            <td>学生id</td>

            <td>学号</td>

            <td>姓名</td>

            <td>性别</td>

        </tr>

        <c:forEach var="student" items="${pageBean.pageList}">

            <tr>

                <td>${student.id}</td>

                <td>${student.scold}</td>

                <td>${student.name}</td>

                <td>${student.sex}</td>

            </tr>

        </c:forEach>

        <tr>

            <td colspan="4">

                当前页数：[${pageBean.currentPage}/${pageBean.pageCount}]

                <a href="student.do?currentPage=1">首页</a>

                <a href="student.do?currentPage=${pageBean.nextPage}">下一页</a>

                <c:forEach begin="${pageBean.startPage}" end="${pageBean.endPage}" var="pageNum">

                    <c:if test="${pageNum == pageBean.currentPage}">

                        ${pageNum}

                    </c:if>

                    <c:if test="${pageNum != pageBean.currentPage}">

                        <a href="student.do?currentPage=${pageNum}">${pageNum}</a>

                    </c:if>

                </c:forEach>

                <a href="student.do?currentPage=${pageBean.previousPage}">上一页</a>

                <a href="student.do?currentPage=${pageBean.pageCount}">尾页</a>

            </td>

        </tr>

    </table>

</div>

</body>

</html>

静下心去理解并且实现出来，会发现并不是很难的。

分页完整项目下载(github)：点我下载