在SpringBoot或者Spring项目中实现最原始的分页功能

不得不感慨自己的写代码水平还是有很大的提升空间，甚至是我觉得很烂来形容吧，近两天一直有一个项目的分页功能很让我头疼，是一个关于SpringBoot的项目，因为可能平时实战项目做的少，由于是学生的原因吧，反正就是自己的不足，导致这个问题困扰着我，又因为忙着考研，所有最近也没时间花心思来慢慢写和整理，但是一直让我焦急万分啊，于是花了两个晚上细细斟酌别人的代码实现，然后开始啥都不看，自己手写实现全面的分页功能，到现在为止总算是小有所成吧，基本完成需求了。后面会学习PageHelper分页插件简化分页的复杂步骤，但是这种原始的写法，自己一定要随手捏来，十分锻炼水平，后面要更加努力的学习了早上再也不能睡到11点了，太颓废（小声逼逼晚上学习带玩熬夜太晚）哈哈哈！

下面是本次实现分页的代码部分：

首先需要一个关于分页的实体类来映射前后端数据，使其具有完整性，也把代码的冗余性降到了最低水准

package com.liuliu.web;

/**
 * @author yuqiliu
 * @create 2020-02-19  22:31
 */
import java.util.List;

public class Page<T> {


    private int pageNo;//当前是第几页


    private List<T> list; //当前显示的图书列表集合


    private int pageSize = 3;//页面的尺寸数


    public long getTotalItemNumber() {
        return totalItemNumber;
    }

    private long totalItemNumber;//总的条目数

    private int totalPageNumber;//总页数


    public Page(int pageNo) {
        super();
        this.pageNo = pageNo;
    }


    public int getPageNo() {
        if(pageNo < 0)
            pageNo = 1;

        if(pageNo > getTotalPageNumber()){
            pageNo = getTotalPageNumber();
        }

        return pageNo;
    }

    public Page() {
    }

    public void setPageNo(int pageNo) {
        this.pageNo = pageNo;
    }

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

    public int getPageSize() {
        return pageSize;
    }

    public void setList(List<T> list) {
        this.list = list;
    }

    public List<T> getList() {
        return list;
    }

    public void setTotalPageNumber(int totalPageNumber) {
        this.totalPageNumber = totalPageNumber;
    }

    public int getTotalPageNumber(){

        totalPageNumber = (int)totalItemNumber / pageSize;

        if(totalItemNumber % pageSize != 0){
            totalPageNumber++;
        }

        return totalPageNumber;
    }

    public void setTotalItemNumber(long totalItemNumber) {
        this.totalItemNumber = totalItemNumber;
    }

    public boolean isHasNext(){
        if(getPageNo() < getTotalPageNumber()){
            return true;
        }

        return false;
    }

    public boolean isHasPrev(){
        if(getPageNo() > 1){
            return true;
        }

        return false;
    }

    public int getPrevPage(){
        if(isHasPrev()){
            return getPageNo() - 1;
        }

        return getPageNo();
    }

    public int getNextPage(){
        if(isHasNext()){
            return getPageNo() + 1;
        }

        return getPageNo();
    }
}

下面从Dao -> Service -> Controller重新梳理一遍我的结论过程

Book.java

package com.liuliu.pojo;

import java.sql.Date;

public class Book {
	
	private Integer id;
	private String author;
	
	private String title;
	private float price;
	
	private Date publishingDate;
	private int salesAmount;
	
	private int storeNumber;
	private String remark;
	
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getAuthor() {
		return author;
	}
	public void setAuthor(String author) {
		this.author = author;
	}
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}
	public float getPrice() {
		return price;
	}
	public void setPrice(float price) {
		this.price = price;
	}
	public Date getPublishingDate() {
		return publishingDate;
	}
	public void setPublishingDate(Date publishingDate) {
		this.publishingDate = publishingDate;
	}
	public int getSalesAmount() {
		return salesAmount;
	}
	public void setSalesAmount(int salesAmount) {
		this.salesAmount = salesAmount;
	}
	public int getStoreNumber() {
		return storeNumber;
	}
	public void setStoreNumber(int storeNumber) {
		this.storeNumber = storeNumber;
	}
	public String getRemark() {
		return remark;
	}
	public void setRemark(String remark) {
		this.remark = remark;
	}
	@Override
	public String toString() {
		return "Book [id=" + id + ", author=" + author + ", title=" + title
				+ ", price=" + price + ", publishingDate=" + publishingDate
				+ ", salesAmount=" + salesAmount + ", storeNumber="
				+ storeNumber + ", remark=" + remark + "]

";
	}
	
	
		
}

BookDao.java

package com.liuliu.mapper;

import com.liuliu.pojo.Book;
import com.liuliu.web.Page;
import org.apache.ibatis.annotations.Mapper;
import org.springframework.stereotype.Repository;

import java.sql.SQLException;
import java.util.HashMap;
import java.util.List;

/**
 * @author yuqiliu
 * @create 2020-02-19  0:18
 */

@Mapper
@Repository
public interface BookDAO {



    //获取全部书籍
    public List<Book> queryAllbook();

    //分页查询操作
    public Page selectByPage(int currentPage,int pageSize,HashMap<String,Object> map)throws SQLException;

    //获取总的书籍数量
    public int totalItemNumber();

    //当页的数据
    public List<Book> selectByPageItem(HashMap<String,Object> map);


}

BookMapper.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.liuliu.mapper.BookDAO">

    <select id="queryAllbook" resultType="Book">
        select * from bookstore.mybooks
    </select>

    
    <select id="selectByPageItem" resultType="Book" parameterType="map">
        select * from bookstore.mybooks limit #{startIndex} ,#{pageSize}
    </select>


    <select id="totalItemNumber" resultType="int">
        select count(*) from bookstore.mybooks
    </select>

</mapper>

BookService.java

package com.liuliu.service;

import com.liuliu.pojo.Book;
import com.liuliu.web.Page;
import org.springframework.stereotype.Service;

import java.sql.SQLException;
import java.util.HashMap;
import java.util.List;

/**
 * @author yuqiliu
 * @create 2020-02-19  0:32
 */


@Service
public interface BookService {

    public List<Book> queryAllbook();

    public Page selectByPage(int currentPage,int pageSize,HashMap<String,Object> map)throws SQLException;
    

//---------------------------------------------------------------------------------------------------


    //获取总的书籍数量
    public int totalItemNumber();


    //当页的数据
    public List<Book> selectByPageItem(HashMap<String,Object> map);

}

BookServiceImpl.java

package com.liuliu.serviceImpl;

import com.liuliu.mapper.BookDAO;
import com.liuliu.pojo.Book;
import com.liuliu.service.BookService;
import com.liuliu.web.Page;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.sql.SQLException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author yuqiliu
 * @create 2020-02-19  0:33
 */


@Service
public class BookServiceImpl implements BookService {

    @Autowired
    private BookDAO bookDAO;

    @Override
    public List<Book> queryAllbook() {
        return null;
    }

    @Override
    public Page selectByPage(int currentPage, int pageSize,HashMap<String,Object> map) throws SQLException {
        Page<Book> page=new Page<>();
        page.setPageNo(currentPage);
        page.setPageSize(pageSize);
        page.setTotalItemNumber(totalItemNumber());
        int totalPageNumber=page.getTotalPageNumber();
        page.setTotalPageNumber(totalPageNumber);
        page.setList(selectByPageItem(map));

        return page;
    }




//-------------------------------------------------------------------------------------------------------
    @Override
    public int totalItemNumber() {
        return bookDAO.totalItemNumber();
    }

    @Override
    public List<Book> selectByPageItem(HashMap<String, Object> map) {
        return bookDAO.selectByPageItem(map);
    }



}

PageController.java

package com.liuliu.controller;

import com.liuliu.serviceImpl.BookServiceImpl;
import com.liuliu.web.Page;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

import javax.servlet.http.HttpServletRequest;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;

/**
 * @author yuqiliu
 * @create 2020-02-20  12:23
 */


@Controller
public class PageController {

    @Autowired
    private BookServiceImpl bookService;

    @GetMapping("/toPage")
    public String pageController(Integer currentPage, Integer pageSize, Model model, HttpServletRequest request) throws SQLException {


        pageSize=3;
        if(request.getParameter("currentPage")==null)
        {
            currentPage=1;
        }
        else
        {
            currentPage=Integer.parseInt(request.getParameter("currentPage"));
        }

        HashMap<String, Object> map = new HashMap<String, Object>();




        System.out.println(currentPage);
        map.put("startIndex",(currentPage-1)*pageSize);
        map.put("pageSize",pageSize);

        Page page = bookService.selectByPage(currentPage, pageSize,map);
        model.addAttribute("pageBean",page);
        return "index";
    }
}

前端使用的是 Thymeleaf 模板引擎渲染

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>图书展示首页</title>
    <style type="text/css">
        .table{
             80%;
            margin: auto;
        }
        .tableCenter{
            text-align: center;
        }
    </style>
</head>
<body>

<form th:action="@{/toPage}" th:method="get">
            <div class="tableCenter">
                <table class="table" width="700" style="table-layout: fixed;">
                    <thead>
                    <th>ID</th>
                    <th>Author</th>
                    <th>Title</th>
                    <th>Price</th>
                    <th>PublishingDate</th>
                    <th>SalesAmount</th>
                    <th>StoreNumber</th>
                    <th>Remark</th>
                    </thead>
                    <tbody>
                    <tr th:each="Book:${pageBean.list}">
                        <td th:text="${Book.id}"></td>
                        <td th:text="${Book.author}"></td>
                        <td th:text="${Book.title}"></td>
                        <td th:text="${Book.price}"></td>
                        <td th:text="${Book.publishingDate}"></td>
                        <td th:text="${Book.salesAmount}"></td>
                        <td th:text="${Book.storeNumber}"></td>
                        <td th:text="${Book.remark}"></td>
                    </tr>

                    <tr>
                        <td colspan="8">
                            第 [[${pageBean.pageNo}]] /  [[${pageBean.totalPageNumber}]]
                                每页显示[[${pageBean.pageSize}]]条  &nbsp;&nbsp;&nbsp;
                                总的记录数[[${pageBean.totalItemNumber}]] &nbsp;&nbsp;&nbsp;
                            &nbsp;&nbsp;
                                <a th:href="@{/toPage(currentPage=1)}" th:if="${pageBean.pageNo != 1 }">首页</a>
                                <a th:href="@{/toPage(currentPage=${(pageBean.pageNo)-1})}" th:if="${pageBean.pageNo != 1}">上一页</a>


                            <a th:each="i : ${#numbers.sequence(1,pageBean.totalPageNumber)}"
                               th:if="${pageBean.pageNo==i}">[[${i}]]</a>

                            <a th:each="i : ${#numbers.sequence(1,pageBean.totalPageNumber)}"
                                th:href="@{/toPage(currentPage=${i})}">[[${i}]]</a>


                                <a th:if="${pageBean.pageNo != pageBean.totalPageNumber}"
                                   th:href="@{/toPage(currentPage=${pageBean.pageNo+1})}">下一页</a>
                                <a th:if="${pageBean.pageNo != pageBean.totalPageNumber}"
                                   th:href="@{/toPage(currentPage=${pageBean.totalPageNumber})}">尾页</a>

                            转到 <input type="text" size="1" name="currentPage"/> 页
                        </td>
                    </tr>

                    </tbody>
                </table>

            </div>

</form>

</body>
</html>

注：本次分页的成功源于知乎上收藏的两篇文章，对我提供了很大的帮助，所有以后对纯手写的分页功能还有疑问的话可以去知乎上搜索回顾

奉上本次分页项目的效果图，虽然前端样式简陋，但是所有分页的功能应有尽有