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
@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。（这份阿里 Java 开发手册可以关注公众号Java核心技术，回复：手册）
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);
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
- 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
- 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; }
