重点1：PageInfo的输出结果

1、PageInfo的源代码

public class PageInfo<T> implements Serializable {
    private static final long serialVersionUID = 1L;
    //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;
    //总记录数
    private long total;
    //总页数
    private int pages;
    //结果集
    private List<T> list;

    //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) {
        if (list instanceof Page) {
            Page page = (Page) list;
            this.pageNum = page.getPageNum();
            this.pageSize = page.getPageSize();

            this.pages = page.getPages();
            this.list = page;
            this.size = page.size();
            this.total = page.getTotal();
            //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.list = list;
            this.size = list.size();
            this.total = 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();
        }
    }
}

重点2：具体的使用

 //使用分页插件
            //传入查询的页码，以及显示的条数
            PageHelper.startPage(pn, 10);
            List<Book> bookList = bookService.findBookByCategory(cId);
            //使用pageInfo包装查询后的结果，封装了详细的查询数据，其中参数5是页码导航连续显示的页数
            PageInfo pageInfo = new PageInfo(bookList,5);
            //使用model进行返回
            //model.addAttribute("pageInfo", page);
            //对于ajax返回json数据，可以使用一个Msg类，方便浏览器更方便解析
            return Msg.success().add("pageInfo", pageInfo);

可以直接返回pageInfo,可以得到如下的信息：

{“pageNum”:1,”pageSize”:10,”size”:10,”startRow”:1,”endRow”:10,”total”:64,”pages”:7,”list”:[{“bId”:2,”bName”:”java学习”,”price”:20.0,”author”:”jj”,”cId”:1,”category”:{“cId”:1,”cName”:”学习用书”}},{“bId”:12,”bName”:”dang_9_书1”,”price”:20.1,”author”:”saka1”,”cId”:1,”category”:{“cId”:1,”cName”:”学习用书”}},{“bId”:18,”bName”:”dang_15_书1”,”price”:20.1,”author”:”saka1”,”cId”:1,”category”:{“cId”:1,”cName”:”学习用书”}},{“bId”:21,”bName”:”dang_18_书1”,”price”:20.1,”author”:”saka1”,”cId”:1,”category”:{“cId”:1,”cName”:”学习用书”}},{“bId”:24,”bName”:”dang_21_书1”,”price”:20.1,”author”:”saka1”,”cId”:1,”category”:{“cId”:1,”cName”:”学习用书”}},{“bId”:27,”bName”:”dang_24_书1”,”price”:20.1,”author”:”saka1”,”cId”:1,”category”:{“cId”:1,”cName”:”学习用书”}},{“bId”:30,”bName”:”dang_27_书1”,”price”:20.1,”author”:”saka1”,”cId”:1,”category”:{“cId”:1,”cName”:”学习用书”}},{“bId”:33,”bName”:”dang_30_书1”,”price”:20.1,”author”:”saka1”,”cId”:1,”category”:{“cId”:1,”cName”:”学习用书”}},{“bId”:36,”bName”:”dang_33_书1”,”price”:20.1,”author”:”saka1”,”cId”:1,”category”:{“cId”:1,”cName”:”学习用书”}},{“bId”:39,”bName”:”dang_36_书1”,”price”:20.1,”author”:”saka1”,”cId”:1,”category”:{“cId”:1,”cName”:”学习用书”}}],”prePage”:0,”nextPage”:2,”isFirstPage”:true,”isLastPage”:false,”hasPreviousPage”:false,”hasNextPage”:true,”navigatePages”:5,”navigatepageNums”:[1,2,3,4,5],”navigateFirstPage”:1,”navigateLastPage”:5,”lastPage”:5,”firstPage”:1}

在此可以看出，list中存放的信息时在使用的第三个构造方法所传递的所查询的book的信息

再比如:

/**
     * 分页查询
     *
     * @param vo
     * @return
     */
    @Override
    public PageInfo<Article> findPageBreakByCondition(ArticleConditionVO vo) {
        PageHelper.startPage(vo.getPageNumber(), vo.getPageSize());
        List<BizArticle> list = bizArticleMapper.findPageBreakByCondition(vo);
        if (CollectionUtils.isEmpty(list)) {
            return null;
        }
        List<Long> ids = new ArrayList<>();
        for (BizArticle bizArticle : list) {
            ids.add(bizArticle.getId());
        }
        List<BizArticle> listTag = bizArticleMapper.listTagsByArticleId(ids);
        // listTag, 重新组装数据为{id: Article}
        Map<Long, BizArticle> tagMap = new LinkedHashMap<>(listTag.size());
        for (BizArticle bizArticle : listTag) {
            tagMap.put(bizArticle.getId(), bizArticle);
        }

        List<Article> boList = new LinkedList<>();
        for (BizArticle bizArticle : list) {
            BizArticle tagArticle = tagMap.get(bizArticle.getId());
            bizArticle.setTags(tagArticle.getTags());
            boList.add(new Article(bizArticle));
        }
        PageInfo bean = new PageInfo<BizArticle>(list);
        bean.setList(boList);
        return bean;
    }

再或者

package com.app.controller;

import java.util.ArrayList;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

import com.app.entity.User;
import com.app.servcie.UserService;
import com.github.pagehelper.PageHelper;
import com.github.pagehelper.PageInfo;

@Controller
public class UserController {
    @Autowired
    private UserService userService;

    @RequestMapping("/insertUser")
    @ResponseBody
    public User insertUser(User user) {
        userService.saveUser(user);
        User resultUser = userService.findUserById(user.getId());
        return resultUser;
    }

    @RequestMapping("/getAllUser")
    @ResponseBody
    public List<User> getAllUser(@RequestParam(required = false, defaultValue = "1") Integer startPage,
            @RequestParam(required = false, defaultValue = "5") Integer PageSize) {
        PageHelper.startPage(startPage, PageSize);
        List<User> users = new ArrayList<>();
        users = userService.findAllUser();
        PageInfo<User> pi = new PageInfo<>(users);
        return users;
    }
}

重点3：Page

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);
    }
}

注意：page是一个ArryaList的抽象类！

重点4：Pagehelper

public class PageHelper extends PageMethod implements Dialect {
    private PageParams pageParams;
    private PageAutoDialect autoDialect;

    @Override
    public boolean skip(MappedStatement ms, Object parameterObject, RowBounds rowBounds) {
        if(ms.getId().endsWith(MSUtils.COUNT)){
            throw new RuntimeException("在系统中发现了多个分页插件，请检查系统配置!");
        }
        Page page = pageParams.getPage(parameterObject, rowBounds);
        if (page == null) {
            return true;
        } else {
            //设置默认的 count 列
            if(StringUtil.isEmpty(page.getCountColumn())){
                page.setCountColumn(pageParams.getCountColumn());
            }
            autoDialect.initDelegateDialect(ms);
            return false;
        }
    }

    @Override
    public boolean beforeCount(MappedStatement ms, Object parameterObject, RowBounds rowBounds) {
        return autoDialect.getDelegate().beforeCount(ms, parameterObject, rowBounds);
    }

    @Override
    public String getCountSql(MappedStatement ms, BoundSql boundSql, Object parameterObject, RowBounds rowBounds, CacheKey countKey) {
        return autoDialect.getDelegate().getCountSql(ms, boundSql, parameterObject, rowBounds, countKey);
    }

    @Override
    public boolean afterCount(long count, Object parameterObject, RowBounds rowBounds) {
        return autoDialect.getDelegate().afterCount(count, parameterObject, rowBounds);
    }

    @Override
    public Object processParameterObject(MappedStatement ms, Object parameterObject, BoundSql boundSql, CacheKey pageKey) {
        return autoDialect.getDelegate().processParameterObject(ms, parameterObject, boundSql, pageKey);
    }
    .............
}

前端使用：

<#-- 分页组件 -->
<#macro pageBar>
    <#if page?exists && (page.pages > 1)>
    <nav class="pagination"
         data-url="${config.siteUrl}/${url?if_exists}"
         data-search="${(model.keywords == null || model.keywords == '')?string('false', 'true')}"
         data-total-page="${page.pages?c}"
         data-current-page="${page.pageNum?c}"
         data-pre="${page.prePage}"
         data-next="${page.nextPage}"></nav>
    </#if>
</#macro>