用pageInfo对List手工分页

因业务需要，需对List，进行分页。

List来源，多种多样，有时不能用数据库发送sql来进行limit的分页

思路：

1.对List数组来源，进行subList的截取，类似于数据库发送limit。

2.构建一个pageinfo的工具类。

List<Description> descriptionByCategoryList = descriptionService.getDescriptionByCategoryList(20);

        int fromIndex = 0;
        int toIndex = 0;
        int pageSize = 20;
        int pageIndex = pn;
        int total = descriptionByCategoryList.size(); // 取出总记录数
        if (total / pageSize == 0 && total % pageSize > 0) {
            fromIndex = 0;
            toIndex = total;
        } else {
            if (total / pageSize >= 1 && total % pageSize >= 0) {
                fromIndex = pageSize * (pageIndex - 1);
                if (pageSize * pageIndex >= total) {
                    toIndex = total;
                } else {
                    toIndex = pageSize * pageIndex;
                }
            }
        }

　　//做pn越界处理

    try {
          descriptionByCategoryList =descriptionByCategoryList.subList(fromIndex, toIndex);
     } catch (IndexOutOfBoundsException e) {
        fromIndex = 0;
        toIndex= pageSize;
        descriptionByCategoryList =descriptionByCategoryList.subList(fromIndex, toIndex);
      }catch(IllegalArgumentException e) {
         fromIndex = total-pageSize;
         toIndex =total;
      descriptionByCategoryList =descriptionByCategoryList.subList(fromIndex, toIndex);
     }

        descriptionByCategoryList = descriptionByCategoryList.subList(fromIndex, toIndex);  //进行分页  
        PageInfo<Description> page = new PageInfo<Description>(descriptionByCategoryList, 7);
        page = PageHelperTool.initPageInfoObj(pageIndex, total, pageSize, page);  //调用分页工具
        mv.addObject("pageinfo", page);

分页工具类

package cn.taotao.utils;

import com.github.pagehelper.PageInfo;

/**
  * @Title: PageHelperTool.java
 * @Package
 * @Description: 分页工具类
 */
public class PageHelperTool {
    /**
     * PageHelper中，如果当前页是最后一页，则返回的nextPage是0，即首页，而有时我们需要最后一页的nextPage是lastPage，因此写此方法
     * 
     * @param currentPage
     * @param pageObj
     * @return
     */
    public static <T> PageInfo<T> lastPageSetNextPage(int currentPage, PageInfo<T> pageObj) {
        if (currentPage == pageObj.getPages()) {
            pageObj.setNextPage(pageObj.getPages());
        }
        return pageObj;
    }

    public static <T> PageInfo<T> initPageInfoObj(int currentPage, int total, int pageSize, PageInfo<T> pageInfo) {
        pageInfo.setNextPage(currentPage < ((total + pageSize - 1) / pageSize) ? currentPage + 1 : currentPage);
        pageInfo.setTotal(total);
        pageInfo.setPageNum(currentPage);
        pageInfo.setPages((total + pageSize - 1) / pageSize);
        pageInfo.setLastPage((total + pageSize - 1) / pageSize);
        pageInfo.setPrePage(currentPage > 1 ? currentPage - 1 : currentPage);
        pageInfo.setIsFirstPage(currentPage == 1 ? true : false);
        pageInfo.setIsLastPage(currentPage == (total + pageSize - 1) / pageSize ? true : false);
        pageInfo.setHasPreviousPage(currentPage == 1 ? false : true);
        pageInfo.setHasNextPage(currentPage == (total + pageSize - 1) / pageSize ? false : true);
        return calcNavigatepageNums(pageInfo);
    }

    private static <T> PageInfo<T> calcNavigatepageNums(PageInfo<T> pageInfo) {
        // 当总页数小于或等于导航页码数时
        if (pageInfo.getPages() <= pageInfo.getNavigatePages()) {
            pageInfo.setNavigatepageNums(new int[pageInfo.getPages()]);
            for (int i = 0; i < pageInfo.getPages(); i++) {
                pageInfo.getNavigatepageNums()[i] = i + 1;
            }
        } else { // 当总页数大于导航页码数时
            pageInfo.setNavigatepageNums(new int[pageInfo.getNavigatePages()]);
            int startNum = pageInfo.getPageNum() - pageInfo.getNavigatePages() / 2;
            int endNum = pageInfo.getPageNum() + pageInfo.getNavigatePages() / 2;

            if (startNum < 1) {
                startNum = 1;
                // (最前navigatePages页
                for (int i = 0; i < pageInfo.getNavigatePages(); i++) {
                    pageInfo.getNavigatepageNums()[i] = startNum++;
                }
            } else if (endNum > pageInfo.getPages()) {
                endNum = pageInfo.getPages();
                // 最后navigatePages页
                for (int i = pageInfo.getNavigatePages() - 1; i >= 0; i--) {
                    pageInfo.getNavigatepageNums()[i] = endNum--;
                }
            } else {
                // 所有中间页
                for (int i = 0; i < pageInfo.getNavigatePages(); i++) {
                    pageInfo.getNavigatepageNums()[i] = startNum++;
                }
            }
        }
        return pageInfo;
    }

}

题外另外，需要在排序的类，重写自定义compare的规则。就是说，让他知道如何排序