说明：
（1） 为什么写本篇博客？：
● 在【SpringBoot电商项目商品分类模块后台的分类列表平铺接口】中，实现分页功能时，使用到了PageHelper分页插件；
● 但是，在【SpringBoot电商项目商品分类模块后台的分类列表平铺接口】中，我们使用的是PageHelper中的PageInfo对象；
● 而，在【MyBatis进阶五：PageHelper分页插件；】中，我们第一次遇到PageHelper时候，使用的是PageHelper中的Page对象；
● 所以，本篇博客，就分析一下：PageHelper分页插件中的：Page和PageInfo的区别；
（2） 本篇博客参考的博客有：
●【Page和PageInfo】，该文的作者是【程序员^晓洋】；
一：Page和PageInfo；（这儿，归纳了两个对象的属性，总结的不错；）
这儿的内容，完全照抄自【Page和PageInfo】，该文的作者是【程序员^晓洋】；
1. Page和PageInfo简介；
两者都能获取到数据，
Page是一个ArrayListList。
PageInfo是一个对象，能获取到的数据比Page多；
2.Page和PageInfo，具体属性分析；
Page对象：
private int pageNum; //当前页码
private int pageSize; //每页数据的数量
private int startRow; //始页首行行号
private int endRow; //尾页尾行行号
private long total; //总记录数
private int pages; //总页数
private Boolean reasonable; //分页合理化
private Boolean pageSizeZero;
//当设置为true的时候，如果pagesize设置为0（或RowBounds的limit=0），就不执行分页，返回全部结果PageInfo对象：
private int pageNum; //当前页
private int pageSize; //每页显示数据条数
private int size; //当前页的数量
private int startRow; //始页首行行号
private int endRow; //尾页尾行行号
private long total; //总记录数
private int pages; //总页数
private List<T list; //查询结果的数据
private int firstPage; //首页
private int prePage; //上一页
private int nextPage; // 下一页
private int lastPage; //最后一页
private boolean isFirstPage; //是不是第一页
private boolean isLastPage; //是不是最后一页
private boolean hasPreviousPage;//有没有上一页
private boolean hasNextPage; //有没有下一页
private int navigatePages; //所有导航页号
private int[] navigatepageNums; //导航页码数
二：Page和PageInfo：源码；（这部分，仅供参考，爱看不看）
1.Page源码；
/*
* The MIT License (MIT)
*
* Copyright (c) 2014-2017 [email protected]
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.github.pagehelper;
import java.io.Closeable;
import java.util.ArrayList;
import java.util.List;
/**
* Mybatis - 分页对象
*
* @author liuzh/abel533/isea533
* @version 3.6.0
* 项目地址 : http://git.oschina.net/free/Mybatis_PageHelper
*/
public class Page<E> extends ArrayList<E> implements Closeable {
private static final long serialVersionUID = 1L;
/**
* 页码，从1开始
*/
private int pageNum;
/**
* 页面大小
*/
private int pageSize;
/**
* 起始行
*/
private int startRow;
/**
* 末行
*/
private int endRow;
/**
* 总数
*/
private long total;
/**
* 总页数
*/
private int pages;
/**
* 包含count查询
*/
private boolean count = true;
/**
* 分页合理化
*/
private Boolean reasonable;
/**
* 当设置为true的时候，如果pagesize设置为0（或RowBounds的limit=0），就不执行分页，返回全部结果
*/
private Boolean pageSizeZero;
/**
* 进行count查询的列名
*/
private String countColumn;
/**
* 排序
*/
private String orderBy;
/**
* 只增加排序
*/
private boolean orderByOnly;
public Page() {
super();
}
public Page(int pageNum, int pageSize) {
this(pageNum, pageSize, true, null);
}
public Page(int pageNum, int pageSize, boolean count) {
this(pageNum, pageSize, count, null);
}
private Page(int pageNum, int pageSize, boolean count, Boolean reasonable) {
super(0);
if (pageNum == 1 && pageSize == Integer.MAX_VALUE) {
pageSizeZero = true;
pageSize = 0;
}
this.pageNum = pageNum;
this.pageSize = pageSize;
this.count = count;
calculateStartAndEndRow();
setReasonable(reasonable);
}
/**
* int[] rowBounds
* 0 : offset
* 1 : limit
*/
public Page(int[] rowBounds, boolean count) {
super(0);
if (rowBounds[0] == 0 && rowBounds[1] == Integer.MAX_VALUE) {
pageSizeZero = true;
this.pageSize = 0;
} else {
this.pageSize = rowBounds[1];
this.pageNum = rowBounds[1] != 0 ? (int) (Math.ceil(((double) rowBounds[0] + rowBounds[1]) / rowBounds[1])) : 0;
}
this.startRow = rowBounds[0];
this.count = count;
this.endRow = this.startRow + rowBounds[1];
}
public List<E> getResult() {
return this;
}
public int getPages() {
return pages;
}
public Page<E> setPages(int pages) {
this.pages = pages;
return this;
}
public int getEndRow() {
return endRow;
}
public Page<E> setEndRow(int endRow) {
this.endRow = endRow;
return this;
}
public int getPageNum() {
return pageNum;
}
public Page<E> setPageNum(int pageNum) {
//分页合理化，针对不合理的页码自动处理
this.pageNum = ((reasonable != null && reasonable) && pageNum <= 0) ? 1 : pageNum;
return this;
}
public int getPageSize() {
return pageSize;
}
public Page<E> setPageSize(int pageSize) {
this.pageSize = pageSize;
return this;
}
public int getStartRow() {
return startRow;
}
public Page<E> setStartRow(int startRow) {
this.startRow = startRow;
return this;
}
public long getTotal() {
return total;
}
public void setTotal(long total) {
this.total = total;
if (total == -1) {
pages = 1;
return;
}
if (pageSize > 0) {
pages = (int) (total / pageSize + ((total % pageSize == 0) ? 0 : 1));
} else {
pages = 0;
}
//分页合理化，针对不合理的页码自动处理
if ((reasonable != null && reasonable) && pageNum > pages) {
if(pages!=0){
pageNum = pages;
}
calculateStartAndEndRow();
}
}
public Boolean getReasonable() {
return reasonable;
}
public Page<E> setReasonable(Boolean reasonable) {
if (reasonable == null) {
return this;
}
this.reasonable = reasonable;
//分页合理化，针对不合理的页码自动处理
if (this.reasonable && this.pageNum <= 0) {
this.pageNum = 1;
calculateStartAndEndRow();
}
return this;
}
public Boolean getPageSizeZero() {
return pageSizeZero;
}
public Page<E> setPageSizeZero(Boolean pageSizeZero) {
if (pageSizeZero != null) {
this.pageSizeZero = pageSizeZero;
}
return this;
}
public String getOrderBy() {
return orderBy;
}
public <E> Page<E> setOrderBy(String orderBy) {
this.orderBy = orderBy;
return (Page<E>) this;
}
public boolean isOrderByOnly() {
return orderByOnly;
}
public void setOrderByOnly(boolean orderByOnly) {
this.orderByOnly = orderByOnly;
}
/**
* 计算起止行号
*/
private void calculateStartAndEndRow() {
this.startRow = this.pageNum > 0 ? (this.pageNum - 1) * this.pageSize : 0;
this.endRow = this.startRow + this.pageSize * (this.pageNum > 0 ? 1 : 0);
}
public boolean isCount() {
return this.count;
}
public Page<E> setCount(boolean count) {
this.count = count;
return this;
}
/**
* 设置页码
*
* @param pageNum
* @return
*/
public Page<E> pageNum(int pageNum) {
//分页合理化，针对不合理的页码自动处理
this.pageNum = ((reasonable != null && reasonable) && pageNum <= 0) ? 1 : pageNum;
return this;
}
/**
* 设置页面大小
*
* @param pageSize
* @return
*/
public Page<E> pageSize(int pageSize) {
this.pageSize = pageSize;
calculateStartAndEndRow();
return this;
}
/**
* 是否执行count查询
*
* @param count
* @return
*/
public Page<E> count(Boolean count) {
this.count = count;
return this;
}
/**
* 设置合理化
*
* @param reasonable
* @return
*/
public Page<E> reasonable(Boolean reasonable) {
setReasonable(reasonable);
return this;
}
/**
* 当设置为true的时候，如果pagesize设置为0（或RowBounds的limit=0），就不执行分页，返回全部结果
*
* @param pageSizeZero
* @return
*/
public Page<E> pageSizeZero(Boolean pageSizeZero) {
setPageSizeZero(pageSizeZero);
return this;
}
/**
* 指定 count 查询列
*
* @param columnName
* @return
*/
public Page<E> countColumn(String columnName) {
this.countColumn = columnName;
return this;
}
public PageInfo<E> toPageInfo() {
PageInfo<E> pageInfo = new PageInfo<E>(this);
return pageInfo;
}
public PageSerializable<E> toPageSerializable() {
PageSerializable<E> serializable = new PageSerializable<E>(this);
return serializable;
}
public <E> Page<E> doSelectPage(ISelect select) {
select.doSelect();
return (Page<E>) this;
}
public <E> PageInfo<E> doSelectPageInfo(ISelect select) {
select.doSelect();
return (PageInfo<E>) this.toPageInfo();
}
public <E> PageSerializable<E> doSelectPageSerializable(ISelect select) {
select.doSelect();
return (PageSerializable<E>) this.toPageSerializable();
}
public long doCount(ISelect select) {
this.pageSizeZero = true;
this.pageSize = 0;
select.doSelect();
return this.total;
}
public String getCountColumn() {
return countColumn;
}
public void setCountColumn(String countColumn) {
this.countColumn = countColumn;
}
@Override
public String toString() {
return "Page{" +
"count=" + count +
", pageNum=" + pageNum +
", pageSize=" + pageSize +
", startRow=" + startRow +
", endRow=" + endRow +
", total=" + total +
", pages=" + pages +
", reasonable=" + reasonable +
", pageSizeZero=" + pageSizeZero +
'}' + super.toString();
}
@Override
public void close() {
PageHelper.clearPage();
}
}2.PageInfo源码；
/*
* The MIT License (MIT)
*
* Copyright (c) 2014-2017 [email protected]
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.github.pagehelper;
import java.util.Collection;
import java.util.List;
/**
* 对Page<E>结果进行包装
* <p/>
* 新增分页的多项属性，主要参考:http://bbs.csdn.net/topics/360010907
*
* @author liuzh/abel533/isea533
* @version 3.3.0
* @since 3.2.2
* 项目地址 : http://git.oschina.net/free/Mybatis_PageHelper
*/
@SuppressWarnings({"rawtypes", "unchecked"})
public class PageInfo<T> extends PageSerializable<T> {
//当前页
private int pageNum;
//每页的数量
private int pageSize;
//当前页的数量
private int size;
//由于startRow和endRow不常用，这里说个具体的用法
//可以在页面中"显示startRow到endRow 共size条数据"
//当前页面第一个元素在数据库中的行号
private int startRow;
//当前页面最后一个元素在数据库中的行号
private int endRow;
//总页数
private int pages;
//前一页
private int prePage;
//下一页
private int nextPage;
//是否为第一页
private boolean isFirstPage = false;
//是否为最后一页
private boolean isLastPage = false;
//是否有前一页
private boolean hasPreviousPage = false;
//是否有下一页
private boolean hasNextPage = false;
//导航页码数
private int navigatePages;
//所有导航页号
private int[] navigatepageNums;
//导航条上的第一页
private int navigateFirstPage;
//导航条上的最后一页
private int navigateLastPage;
public PageInfo() {
}
/**
* 包装Page对象
*
* @param list
*/
public PageInfo(List<T> list) {
this(list, 8);
}
/**
* 包装Page对象
*
* @param list page结果
* @param navigatePages 页码数量
*/
public PageInfo(List<T> list, int navigatePages) {
super(list);
if (list instanceof Page) {
Page page = (Page) list;
this.pageNum = page.getPageNum();
this.pageSize = page.getPageSize();
this.pages = page.getPages();
this.size = page.size();
//由于结果是>startRow的，所以实际的需要+1
if (this.size == 0) {
this.startRow = 0;
this.endRow = 0;
} else {
this.startRow = page.getStartRow() + 1;
//计算实际的endRow（最后一页的时候特殊）
this.endRow = this.startRow - 1 + this.size;
}
} else if (list instanceof Collection) {
this.pageNum = 1;
this.pageSize = list.size();
this.pages = this.pageSize > 0 ? 1 : 0;
this.size = list.size();
this.startRow = 0;
this.endRow = list.size() > 0 ? list.size() - 1 : 0;
}
if (list instanceof Collection) {
this.navigatePages = navigatePages;
//计算导航页
calcNavigatepageNums();
//计算前后页，第一页，最后一页
calcPage();
//判断页面边界
judgePageBoudary();
}
}
public static <T> PageInfo<T> of(List<T> list) {
return new PageInfo<T>(list);
}
public static <T> PageInfo<T> of(List<T> list, int navigatePages) {
return new PageInfo<T>(list, navigatePages);
}
/**
* 计算导航页
*/
private void calcNavigatepageNums() {
//当总页数小于或等于导航页码数时
if (pages <= navigatePages) {
navigatepageNums = new int[pages];
for (int i = 0; i < pages; i++) {
navigatepageNums[i] = i + 1;
}
} else { //当总页数大于导航页码数时
navigatepageNums = new int[navigatePages];
int startNum = pageNum - navigatePages / 2;
int endNum = pageNum + navigatePages / 2;
if (startNum < 1) {
startNum = 1;
//(最前navigatePages页
for (int i = 0; i < navigatePages; i++) {
navigatepageNums[i] = startNum++;
}
} else if (endNum > pages) {
endNum = pages;
//最后navigatePages页
for (int i = navigatePages - 1; i >= 0; i--) {
navigatepageNums[i] = endNum--;
}
} else {
//所有中间页
for (int i = 0; i < navigatePages; i++) {
navigatepageNums[i] = startNum++;
}
}
}
}
/**
* 计算前后页，第一页，最后一页
*/
private void calcPage() {
if (navigatepageNums != null && navigatepageNums.length > 0) {
navigateFirstPage = navigatepageNums[0];
navigateLastPage = navigatepageNums[navigatepageNums.length - 1];
if (pageNum > 1) {
prePage = pageNum - 1;
}
if (pageNum < pages) {
nextPage = pageNum + 1;
}
}
}
/**
* 判定页面边界
*/
private void judgePageBoudary() {
isFirstPage = pageNum == 1;
isLastPage = pageNum == pages || pages == 0;
hasPreviousPage = pageNum > 1;
hasNextPage = pageNum < pages;
}
public int getPageNum() {
return pageNum;
}
public void setPageNum(int pageNum) {
this.pageNum = pageNum;
}
public int getPageSize() {
return pageSize;
}
public void setPageSize(int pageSize) {
this.pageSize = pageSize;
}
public int getSize() {
return size;
}
public void setSize(int size) {
this.size = size;
}
public int getStartRow() {
return startRow;
}
public void setStartRow(int startRow) {
this.startRow = startRow;
}
public int getEndRow() {
return endRow;
}
public void setEndRow(int endRow) {
this.endRow = endRow;
}
public int getPages() {
return pages;
}
public void setPages(int pages) {
this.pages = pages;
}
public int getPrePage() {
return prePage;
}
public void setPrePage(int prePage) {
this.prePage = prePage;
}
public int getNextPage() {
return nextPage;
}
public void setNextPage(int nextPage) {
this.nextPage = nextPage;
}
public boolean isIsFirstPage() {
return isFirstPage;
}
public void setIsFirstPage(boolean isFirstPage) {
this.isFirstPage = isFirstPage;
}
public boolean isIsLastPage() {
return isLastPage;
}
public void setIsLastPage(boolean isLastPage) {
this.isLastPage = isLastPage;
}
public boolean isHasPreviousPage() {
return hasPreviousPage;
}
public void setHasPreviousPage(boolean hasPreviousPage) {
this.hasPreviousPage = hasPreviousPage;
}
public boolean isHasNextPage() {
return hasNextPage;
}
public void setHasNextPage(boolean hasNextPage) {
this.hasNextPage = hasNextPage;
}
public int getNavigatePages() {
return navigatePages;
}
public void setNavigatePages(int navigatePages) {
this.navigatePages = navigatePages;
}
public int[] getNavigatepageNums() {
return navigatepageNums;
}
public void setNavigatepageNums(int[] navigatepageNums) {
this.navigatepageNums = navigatepageNums;
}
public int getNavigateFirstPage() {
return navigateFirstPage;
}
public int getNavigateLastPage() {
return navigateLastPage;
}
public void setNavigateFirstPage(int navigateFirstPage) {
this.navigateFirstPage = navigateFirstPage;
}
public void setNavigateLastPage(int navigateLastPage) {
this.navigateLastPage = navigateLastPage;
}
@Override
public String toString() {
final StringBuilder sb = new StringBuilder("PageInfo{");
sb.append("pageNum=").append(pageNum);
sb.append(", pageSize=").append(pageSize);
sb.append(", size=").append(size);
sb.append(", startRow=").append(startRow);
sb.append(", endRow=").append(endRow);
sb.append(", total=").append(total);
sb.append(", pages=").append(pages);
sb.append(", list=").append(list);
sb.append(", prePage=").append(prePage);
sb.append(", nextPage=").append(nextPage);
sb.append(", isFirstPage=").append(isFirstPage);
sb.append(", isLastPage=").append(isLastPage);
sb.append(", hasPreviousPage=").append(hasPreviousPage);
sb.append(", hasNextPage=").append(hasNextPage);
sb.append(", navigatePages=").append(navigatePages);
sb.append(", navigateFirstPage=").append(navigateFirstPage);
sb.append(", navigateLastPage=").append(navigateLastPage);
sb.append(", navigatepageNums=");
if (navigatepageNums == null) {
sb.append("null");
} else {
sb.append('[');
for (int i = 0; i < navigatepageNums.length; ++i) {
sb.append(i == 0 ? "" : ", ").append(navigatepageNums[i]);
}
sb.append(']');
}
sb.append('}');
return sb.toString();
}
}三：Page和PageInfo：使用；（重要！）
（1）首先，就是开启分页，设置【pageNum：当前页】和【pageSize：每页记录数】；
（2）然后，我们会利用Mybatis，根据上面设置的分页条件，去查询数据库，得到查询结果；
（3）然后，可以根据前端对分页数据格式的要求，可以把（3）中查到的分页数据，包装成Page对象；
（4）或者，包装成PageInfo对象；
（5）使用Page对象还是使用PageInfo对象？
● 目前的个人理解：使用Page对象还是PageInfo对象，需要根据前端的要求，或者说是根据接口对返回数据的格式的要求；
● 比如，在【[Spring Boot电商项目29：商品分类模块八：后台的【分类列表（平铺）】接口；](https://blog.csdn.net/csucsgoat/article/details/123159442】的接口文档要求，接口的返回是：
所以，对于这样的接口要求，很自然就是使用PageInfo对象；