Java中PageHelper分页后对list操作导致分页无效
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pageinfotarget.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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