分页代码编写

public class PageVO<T> implements Iterable<T>, Serializable {

    private List<T> content = new ArrayList<T>();
    private long total;
    private int pageNo;
    private int pageSize;

    public PageVO() {
    }

    public PageVO(List<T> content, long total, int pageNo, int pageSize) {
        this.content = content;
        this.total = total;
        this.pageNo = pageNo;
        this.pageSize = pageSize;
    }

    /**
     * Returns if there is a previous page.
     *
     * @return if there is a previous page.
     */
    public boolean hasPrevious() {
        return getPageNo() > 0;
    }

    /**
     * Returns if there is a next page.
     *
     * @return if there is a next page.
     */
    public boolean hasNext() {
        return getPageNo() + 1 < getTotalPage();
    }

    /**
     * Returns whether the current page is the first one.
     *
     * @return whether the current page is the first one.
     */
    public boolean isFirst() {
        return !hasPrevious();
    }

    /**
     * Returns whether the current  page is the last one.
     *
     * @return whether the current  page is the last one.
     */
    boolean isLast() {
        return !hasNext();
    }

    /**
     * Returns the total amount of elements of all pages.
     *
     * @return the total amount of elements of all pages.
     */
    public long getTotal() {
        return total;
    }

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

    /**
     * Returns the number of total pages.
     *
     * @return the number of total pages
     */
    public int getTotalPage() {
        return getPageSize() == 0 ? 1 : (int) Math.ceil((double) total / (double) getPageSize());
    }

    /**
     * Returns the page content as unmodifiable {@link List}.
     *
     * @return Returns the page content as unmodifiable {@link List}
     */
    public List<T> getContent() {
        return Collections.unmodifiableList(content);
    }

    public void setContent(List<T> content) {
        this.content = content;
    }

    /**
     * Returns whether the current page has content.
     *
     * @return whether the current page has content.
     */
    public boolean hasContent() {
        return getContentSize() > 0;
    }

    /**
     * Returns the number of elements on current page.
     *
     * @return the number of elements on current page.
     */
    public int getContentSize() {
        return content.size();
    }

    /**
     * Returns the number of items of each page.
     *
     * @return the number of items of each page
     */
    public int getPageSize() {
        return pageSize;
    }

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

    /**
     * Returns the number of current page. (Zero-based numbering.)
     *
     * @return the number of current page.
     */
    public int getPageNo() {
        return pageNo;
    }

    /**
     * Set the number of current page. (Zero-based numbering.)
     */
    public void setPageNo(int pageNo) {
        this.pageNo = pageNo;
    }

    public Iterator<T> iterator() {
        return getContent().iterator();
    }
}

public PageVO<ProjectDTO> queryProjectsByQueryDTO(ProjectQueryDTO projectQueryDTO, String order, Integer pageNo, Integer pageSize, String sortBy) {
        // 条件构造器
        QueryWrapper<Project> queryWrapper = new QueryWrapper();
        //...业务条件..
        
        // 构造分页对象
        Page<Project> page = new Page<>(pageNo, pageSize);
        // 处理排序 order值: desc 或者 asc
        if (StringUtils.isNotBlank(order) && StringUtils.isNotBlank(sortBy)) {
            if (order.toLowerCase().equals("asc")) {
                queryWrapper.orderByAsc(sortBy);
            } else if (order.toLowerCase().equals("desc")) {
                queryWrapper.orderByDesc(sortBy);
            }
        } else {
        //默认按发标时间倒序排序
queryWrapper.lambda().orderByDesc(Project::getCreateDate);
        }
        // 执行查询
        IPage<Project> projectIPage = page(page, queryWrapper);
        // ENTITY转换为DTO, 不向外部暴露ENTITY
        List<ProjectDTO> dtoList = convertProjectEntityListToDTOList(projectIPage.getRecords());
        // 封装结果集
        return new PageVO<>(dtoList, projectIPage.getTotal(), pageNo, pageSize);
    }


private List<ProjectDTO> convertProjectEntityListToDTOList(List<Project> projectList) {
        if (projectList == null) {
            return null;
        }
        List<ProjectDTO> dtoList = new ArrayList<>();
        projectList.forEach(project -> {
            ProjectDTO projectDTO = new ProjectDTO();
            BeanUtils.copyProperties(project, projectDTO);
            dtoList.add(projectDTO);
        });
        return dtoList;
    }