JSP的分页

1. 分页在读取数据库里的数据需要用，在以后数据库肯定还会有很多数据，一个页面装不下，所以需要分页功能。数据库查询的分页语句是“SELECT * FROM emp LIMIT 0, 5;”这里0是指起始行，5是查询5行，第二页起始行就是5，每页也是查询5条数据。起始行=（页大小-1）*行数。分页查询还需要知道一共多少页（总页数=数据总数%每页条数==0?数据总数/每页条数:数据总数/每页条数+1）。

2. 代码实现

2.1创建一个emp表多添加几条数据

2.2把需要的架包添加在web下面创建一个lib的文件夹并且添加为库。还得准备工具类没有的找我

（没有的请发私信）

2.3添加emp的实体类

package com.cxyzxc.www.entity;

public class Emp {
    private int eid;
    private String ename;
    private int age;
    private double salary;

    public Emp() {
    }

    public Emp(int eid, String ename, int age, double salary) {
        this.eid = eid;
        this.ename = ename;
        this.age = age;
        this.salary = salary;
    }

    public int getEid() {
        return eid;
    }

    public void setEid(int eid) {
        this.eid = eid;
    }

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    @Override
    public String toString() {
        return "Emp{" +
                "eid=" + eid +
                ", ename='" + ename + '\'' +
                ", age=" + age +
                ", salary=" + salary +
                '}';
    }
}

2.4因为需要用到分页所以也要有个Page实体类进行运算

package com.cxyzxc.www.entity;

public class Page {
//页码
   private Integer pageIndex;
//页大小，就是每页多少条数据
   private Integer pageSize;
//总行数就是一共多少条数据
   private Integer totalCounts;
//总页数
   private Integer totalPages;
//起始行
   private Integer startRows;
//调用两参构造方法
   public Page(Integer pageIndex){
       this(pageIndex,8);
   }

    public Page(Integer pageIndex,Integer pageSize){
        this.pageIndex=pageIndex;
        this.pageSize=pageSize;
//起始行
        this.setStartRows((pageIndex-1) * pageSize);

    }

    public Integer getPageIndex() {
        return pageIndex;
    }

    public void setPageIndex(Integer pageIndex) {
        this.pageIndex = pageIndex;
    }

    public Integer getPageSize() {
        return pageSize;
    }

    public void setPageSize(Integer pageSize) {
        this.pageSize = pageSize;
    }

    public Integer getTotalCounts() {
        return totalCounts;
    }

    public void setTotalCounts(Integer totalCounts) {
        this.totalCounts = totalCounts;
//总页数用三目运算符，总行数模页大小余数为0就是总行数除以页大小，不是就是总行数除以页大小+1
        this.setTotalPages(totalCounts%pageSize==0 ? totalCounts / pageSize : totalCounts / pageSize + 1);
    }

    public Integer getTotalPages() {
        return totalPages;
    }

    public void setTotalPages(Integer totalPages) {
        this.totalPages = totalPages;
    }

    public Integer getStartRows() {
        return startRows;
    }

    public void setStartRows(Integer startRows) {
        this.startRows = startRows;
    }

    @Override
    public String toString() {
        return "Page{" +
                "pageIndex=" + pageIndex +
                ", pageSize=" + pageSize +
                ", totalCounts=" + totalCounts +
                ", totalPages=" + totalPages +
                ", startRows=" + startRows +
                '}';
    }

2.5Dao接口类

package com.cxyzxc.www.dao;

import com.cxyzxc.www.entity.Emp;
import com.cxyzxc.www.entity.Page;

import java.util.List;

public interface EmpDao1 {
//查询所有数据
   public List selectAll(Page page);
//查询行数
   public long selectCount();
}

2.6DaoImpl实现类

package com.cxyzxc.www.dao.Impl;

import com.cxyzxc.www.dao.EmpDao1;
import com.cxyzxc.www.entity.Emp;
import com.cxyzxc.www.entity.Page;
import com.cxyzxc.www.utils.Dbutils;
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 EmpDaoImpl01 implements EmpDao1 {
    private QueryRunner queryRunner = new QueryRunner();

    @Override
    public List selectAll(Page page) {
        List emps= null;
        try {
            emps = queryRunner.query(Dbutils.getConnection(),"select * from emp limit ?,?",new BeanListHandler(Emp.class),page.getStartRows(),page.getPageSize());
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
        return emps;

    }

    @Override
    public long selectCount() {
        try {
            return  queryRunner.query(Dbutils.getConnection(), "select count(*) from emp;",new ScalarHandler<>());
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return 0;
    }
}

2.7controller

package com.cxyzxc.www.controller;

import com.cxyzxc.www.dao.EmpDao1;
import com.cxyzxc.www.dao.Impl.EmpDaoImpl01;
import com.cxyzxc.www.entity.Emp;
import com.cxyzxc.www.entity.Page;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.util.List;

@WebServlet(name = "ServletAll", value = "/ServletAll")
public class ServletAll extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
   //获取页大小
 String pageIndex= request.getParameter("pageIndex");
//当页大小为空要赋值给一个1
    if (pageIndex == null) {
        pageIndex="1";
        request.setAttribute("pageIndex",pageIndex);
    }
//将页大小传进去
     Page page = new Page(Integer.valueOf(pageIndex));
        System.out.println(page);
//调用业务类查询行数
        EmpDao1 empDao1= new EmpDaoImpl01();
//总行数
        long count =empDao1.selectCount();
        page.setTotalCounts((int)count);
//查询所有数据，并将page和emp表的数据存储在作用于中并就行转发到jsp中
        List emps=empDao1.selectAll(page);
        request.setAttribute("emps",emps);
        request.setAttribute("page",page);
        request.getRequestDispatcher("/showAllEmp.jsp").forward(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doGet(request, response);
    }
}

2.8showAllEmp.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>


    


  
emp所有数据

// items="${emps}是获得存储的数据
    
        

    

        
员工编码
        
员工姓名
        
员工年龄
        
员工工资
        
操作
    

            
${emp.eid}
            
${emp.ename}
            
${emp.age}
            
${emp.salary}
            

                修改
                删除
            
        
    
    

        

//页码等于1时是首页
             ">首页
<%--            当前页码大于1--%>
            
                上一页
            
//当前页等于1时就不用跳转给个a标签
            
                上一页
            
<%--    page.pageIndex 是指当前页 ，当前页小于总页数就下一页，页码就需要加1     --%>
            
                 ">下一页 
            
//当前页等于总页数就只用a标签包着
            
                下一页
            
//尾页就是跳转到当前页调到总页数
             ">尾页