Java中PageHelper分页后对list操作导致分页无效
1.问题
阿里巴巴Java开发手册
1.1.PageHelper先开启分页,后对list数据操作
@Override public PageInfo<HdQueryVo> getRecordsByView(int pageNo, int pageSize) { PageHelper.startPage(pageNo,pageSize); List<HdQueryVo> hdQueryVosByView = actionMapper.getActionByView(); List<HdQueryVo> hdQueryVos = new ArrayList<>(); for (HdQueryVo hdQueryVo : hdQueryVosByView) { HdQueryVo hdQueryVoSingle = new HdQueryVo(); hdQueryVoSingle.setHdId(hdQueryVo.getHdId()); hdQueryVoSingle.setHdType(hdQueryVo.getHdType()); hdQueryVoSingle.setHdTitle(hdQueryVo.getHdTitle()); hdQueryVoSingle.setHdStartDate(hdQueryVo.getHdStartDate()); hdQueryVoSingle.setHdEndDate(hdQueryVo.getHdEndDate()); hdQueryVoSingle.setHdStatus(hdQueryVo.getHdStatus()); hdQueryVoSingle.setHdImage(hdQueryVo.getHdImage()); hdQueryVoSingle.setHdNumber(hdQueryVo.getHdNumber()); hdQueryVoSingle.setGmtCreate(hdQueryVo.getGmtCreate()); hdQueryVoSingle.setGmtModified(hdQueryVo.getGmtModified()); hdQueryVoSingle.setUserId(hdQueryVo.getUserId()); if (hdQueryVo.getHdType().equals(0)) { hdQueryVoSingle.setHdJoinUsers(onlineWorksMapper.getOnlineJoinUsers(hdQueryVo.getHdId())); } else { hdQueryVoSingle.setHdJoinUsers(offlineUsersMapper.getOfflineJoinUsers(hdQueryVo.getHdId())); } hdQueryVos.add(hdQueryVoSingle); } PageInfo<HdQueryVo> pageViewInfo = new PageInfo<>(hdQueryVos); return pageViewInfo; }
可以分页,但是数据量错误,total始终等于每页数据量,即pageSize
1.2.先对list数据进行操作,后开启分页
@Override public PageInfo<HdQueryVo> getRecordsByView(int pageNo, int pageSize) { List<HdQueryVo> hdQueryVosByView = actionMapper.getActionByView(); List<HdQueryVo> hdQueryVos = new ArrayList<>(); for (HdQueryVo hdQueryVo : hdQueryVosByView) { HdQueryVo hdQueryVoSingle = new HdQueryVo(); hdQueryVoSingle.setHdId(hdQueryVo.getHdId()); hdQueryVoSingle.setHdType(hdQueryVo.getHdType()); hdQueryVoSingle.setHdTitle(hdQueryVo.getHdTitle()); hdQueryVoSingle.setHdStartDate(hdQueryVo.getHdStartDate()); hdQueryVoSingle.setHdEndDate(hdQueryVo.getHdEndDate()); hdQueryVoSingle.setHdStatus(hdQueryVo.getHdStatus()); hdQueryVoSingle.setHdImage(hdQueryVo.getHdImage()); hdQueryVoSingle.setHdNumber(hdQueryVo.getHdNumber()); hdQueryVoSingle.setGmtCreate(hdQueryVo.getGmtCreate()); hdQueryVoSingle.setGmtModified(hdQueryVo.getGmtModified()); hdQueryVoSingle.setUserId(hdQueryVo.getUserId()); if (hdQueryVo.getHdType().equals(0)) { hdQueryVoSingle.setHdJoinUsers(onlineWorksMapper.getOnlineJoinUsers(hdQueryVo.getHdId())); } else { hdQueryVoSingle.setHdJoinUsers(offlineUsersMapper.getOfflineJoinUsers(hdQueryVo.getHdId())); } hdQueryVos.add(hdQueryVoSingle); } PageHelper.startPage(pageNo,pageSize); PageInfo<HdQueryVo> pageViewInfo = new PageInfo<>(hdQueryVos); return pageViewInfo; }
数据可以查询出来,总数total也正确,但是分页功能失效
2.原因
PageHelper中startPage开启分页方法只对后面的sql查询起作用
1.1 错误原因是提前开启分页后,对list操作,即PageInfo pageViewInfo = new PageInfo<>(hdQueryVos);
/** * 包装Page对象 * * @param list */ public PageInfo(List list) { this(list, 8); }
只是把list转为PageInfo对象,不影响前面分页数据的操作
1.2 错误原因是先对list操作后,开启翻页后没有sql语句
即sql语句没有参与分页查询
3.解决方案
直接对分页后的PageInfo对象中的数据进行操作
①对list集合操作,先取出PageInfo里的list集合数据,再对数据进行相关操作
②将操作完后的list集合再次存到PageInfo里,进行return
@Override public PageInfo<HdQueryVo> getRecordsByView(int pageNo, int pageSize) { PageInfo<HdQueryVo> source = PageHelper.startPage(pageNo, pageSize).doSelectPageInfo(()->{ actionMapper.getActionByView(); }); // 需要转换的对象 PageInfo<HdQueryVo> target = new PageInfo<>(); // 复制分页属性 BeanUtils.copyProperties(source, target); // 对查询的list进行下一步操作,比如类型转换后 List<HdQueryVo> collect = source.getList().stream().collect(Collectors.toList()); List<HdQueryVo> hdQueryVos = new ArrayList<>(); for (HdQueryVo hdQueryVo : collect) { HdQueryVo hdQueryVoSingle = new HdQueryVo(); hdQueryVoSingle.setHdId(hdQueryVo.getHdId()); hdQueryVoSingle.setHdType(hdQueryVo.getHdType()); hdQueryVoSingle.setHdTitle(hdQueryVo.getHdTitle()); hdQueryVoSingle.setHdStartDate(hdQueryVo.getHdStartDate()); hdQueryVoSingle.setHdEndDate(hdQueryVo.getHdEndDate()); hdQueryVoSingle.setHdStatus(hdQueryVo.getHdStatus()); hdQueryVoSingle.setHdImage(hdQueryVo.getHdImage()); hdQueryVoSingle.setHdNumber(hdQueryVo.getHdNumber()); hdQueryVoSingle.setGmtCreate(hdQueryVo.getGmtCreate()); hdQueryVoSingle.setGmtModified(hdQueryVo.getGmtModified()); hdQueryVoSingle.setUserId(hdQueryVo.getUserId()); if (hdQueryVo.getHdType().equals(0)) { hdQueryVoSingle.setHdJoinUsers(onlineWorksMapper.getOnlineJoinUsers(hdQueryVo.getHdId())); } else { hdQueryVoSingle.setHdJoinUsers(offlineUsersMapper.getOfflineJoinUsers(hdQueryVo.getHdId())); } hdQueryVos.add(hdQueryVoSingle); } // 加工后的数据放入新的pageinfo target.setList(hdQueryVos); return target; }
参考资料:
PageHelper官方文档
PageHelper分页查询结果后再对数据List操作的方法
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