JAVA 递归后台代码实现，并封装简单的分页信息

最新推荐文章于 2025-02-22 11:17:29 发布

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页面上要分页展示层级关系的数据信息，很容易就想到递归，我能想到的主要有两种做法：1 在SQL中使用递归，2 一条简单的SQL将所有要展示的信息获取，使用JAVA代码逻辑进行递归封装。

本文采用的是第二种，主要是考虑到如果数据量过大，使用SQL递归感觉查询较慢，页面等待时间过长（自我感觉，并没有实际验证），但由于是采用的第二种做法，导致无法使用PageHelper三连完成分页（此时SQL返回的是所有记录，并没有递归效果，所以此时做分页毫无意义），所以需要使用java代码逻辑实现递归完成后在进行简单的分页封装

PageHelper三连：

/**
* pageNo : 第几页
* pageSize : 每页显示多少条
*/

PageHelper.startPage(pageNo, pageSize);
Page<TestVO> pageTestList = testDao.getListById(id);
PageInfo<TestVO> pageInfo = new PageInfo<>(pageTestList);

以下是实现的简单例子，总结方便自己回顾，也希望可以给其他同学提供一点儿思路

要展示的信息的实体类：

class TeacherAndStudent {

    private Integer id;
    //姓名
    private String name;

    //上级ID
    private Integer superiorId;

    //等级 1校长 2主任 3教师 4学生
    private Integer level;

    private List<TeacherAndStudent> junior;

    public TeacherAndStudent(Integer id, String name, Integer superiorId, Integer level) 
    {
        this.id = id;
        this.name = name;
        this.superiorId = superiorId;
        this.level = level;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getSuperiorId() {
        return superiorId;
    }

    public void setSuperiorId(Integer superiorId) {
        this.superiorId = superiorId;
    }

    public Integer getLevel() {
        return level;
    }

    public void setLevel(Integer level) {
        this.level = level;
    }

    public List<TeacherAndStudent> getJunior() {
        return junior;
    }

    public void setJunior(List<TeacherAndStudent> junior) {
        this.junior = junior;
    }

    @Override
    public String toString() {
        return "TeacherAndStudent{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", superiorId=" + superiorId +
                ", level=" + level +
                ", junior=" + junior +
                '}';
    }
}

分页信息实体类（可以直接从网上扒）：

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;
    //总记录数
    private long total;
    //总页数
    private int pages;
    //结果集
    private List<T> list;
    //是否为第一页
    private boolean isFirstPage = false;
    //是否为最后一页
    private boolean isLastPage = false;


    public PageInfo() {
    }

    /**
     * 包装Page对象
     *
     * @param list
     */
    public PageInfo(List<T> list) {
        if (list instanceof Page) {
            Page page = (Page) list;
            this.pageNum = page.getPageNum();
            this.pageSize = page.getPageSize();

            this.pages = page.getPages();
            this.list = page;
            this.total = page.getTotal();
        } else if (list instanceof Collection) {
            this.pageNum = 1;
            this.pageSize = list.size();

            this.pages = 1;
            this.list = list;
            this.total = list.size();
        }
        if (list instanceof Collection) {
            //判断页面边界
            judgePageBoudary();
        }
    }

    /**
     * 判定页面边界
     */
    private void judgePageBoudary() {
        isFirstPage = pageNum == 1;
        isLastPage = 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 long getTotal() {
        return total;
    }

    public void setTotal(long total) {
        this.total = total;
    }

    public int getPages() {
        return pages;
    }

    public void setPages(int pages) {
        this.pages = pages;
    }

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

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

    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;
    }

    @Override
    public String toString() {
        final StringBuffer sb = new StringBuffer("PageInfo{");
        sb.append("pageNum=").append(pageNum);
        sb.append(", pageSize=").append(pageSize);
        sb.append(", total=").append(total);
        sb.append(", pages=").append(pages);
        sb.append(", list=").append(list);
        sb.append(", isFirstPage=").append(isFirstPage);
        sb.append(", isLastPage=").append(isLastPage);
        sb.append(", navigatepageNums=");
        sb.append('}');
        return sb.toString();
    }
}

递归核心函数：

private static List<TeacherAndStudent> treeList(List<TeacherAndStudent> list, Integer rootId) {
        List <TeacherAndStudent> newList = new ArrayList<>();

        for (TeacherAndStudent teacherAndStudentTemp : list) {
            if(teacherAndStudentTemp.getSuperiorId() == rootId.intValue()) {
                List<TeacherAndStudent> tempList = treeList(list, teacherAndStudentTemp.getId());
                teacherAndStudentTemp.setJunior(tempList);
                newList.add(teacherAndStudentTemp);
            }
        }

        return newList;
    }

主函数以及简单的分页参数：

public static void main(String[] args) {
        List<TeacherAndStudent> list = new ArrayList<>();

        list.add(new TeacherAndStudent(1, "赵校长", 0,1));

        list.add(new TeacherAndStudent(2, "赵主任", 1,2));
        list.add(new TeacherAndStudent(3, "钱主任", 1,2));

        list.add(new TeacherAndStudent(4, "赵老师", 2,3));
        list.add(new TeacherAndStudent(5, "钱老师", 2,3));
        list.add(new TeacherAndStudent(6, "孙老师", 2,3));
        list.add(new TeacherAndStudent(7, "李老师", 2,3));
        list.add(new TeacherAndStudent(8, "周老师", 3,3));
        list.add(new TeacherAndStudent(9, "吴老师", 3,3));

        list.add(new TeacherAndStudent(10, "赵同学", 4,4));
        list.add(new TeacherAndStudent(11, "钱同学", 4,4));
        list.add(new TeacherAndStudent(12, "孙同学", 4,4));
        list.add(new TeacherAndStudent(13, "李同学", 5,4));

        list.add(new TeacherAndStudent(14, "周同学", 5,4));
        list.add(new TeacherAndStudent(15, "吴同学", 6,4));

        List<TeacherAndStudent> newList = treeList(list, 1);

        System.out.println(newList);

        int pageSize = 10;
        int pageNo = 1;

        int totalCount = newList.size();
        int pages = totalCount / pageSize + (totalCount % pageSize == 0 ? 0 : 1);

        int fromIndex = (pageNo - 1 < 0 ? 0 : (pageNo - 1)) * pageSize;
        int toIndex = pageSize * pageNo > totalCount ? totalCount : (pageSize * pageNo);

        boolean isFirstPage = pageNo == 1;
        boolean isLastPage = pageNo == pages;

        PageInfo<TeacherAndStudent> pageHelperResult = new PageInfo<>();
        pageHelperResult.setList(newList.subList(fromIndex, toIndex));
        pageHelperResult.setPageNum(pageNo);
        pageHelperResult.setPageSize(pageSize);
        pageHelperResult.setTotal(totalCount);
        pageHelperResult.setPages(pages);
        pageHelperResult.setIsFirstPage(isFirstPage);
        pageHelperResult.setIsLastPage(isLastPage);

    }

递归查询的结果如下（未分页）：