Java Web(十) 分页功能

1、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。

2、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。

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;
    }
}

PageBean

　　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;
    }


}

Student

3、servlet控制层

　　在Servlet中有三个任务：

　　①获取从网页传来的currentPage(当前页面)

　　②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

　　③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");
        //得到当前页面数
        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);
    }
}

4、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;
    }
}

5、dao数据访问层

　　在dao层里有两个任务：

　　①得到总记录数

　　②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);
    }

}

六、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。