目錄1.問題1.1.PageHelper先開啟分頁，后對(duì)list數(shù)據(jù)操作1.2.先對(duì)list數(shù)據(jù)進(jìn)行操作，后開啟分頁2.原因3.解決方案1.問題

阿里巴巴Java開發(fā)手冊(cè)

1.1.PageHelper先開啟分頁，后對(duì)list數(shù)據(jù)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; }

可以分頁，但是數(shù)據(jù)量錯(cuò)誤，total始終等于每頁數(shù)據(jù)量，即pageSize

1.2.先對(duì)list數(shù)據(jù)進(jìn)行操作，后開啟分頁

@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; }

數(shù)據(jù)可以查詢出來，總數(shù)total也正確，但是分頁功能失效

2.原因

PageHelper中startPage開啟分頁方法只對(duì)后面的sql查詢起作用

1.1 錯(cuò)誤原因是提前開啟分頁后，對(duì)list操作，即PageInfo pageViewInfo = new PageInfo<>(hdQueryVos);

/*** 包裝Page對(duì)象** @param list*/public PageInfo(List list) {this(list, 8);}

只是把list轉(zhuǎn)為PageInfo對(duì)象，不影響前面分頁數(shù)據(jù)的操作

1.2 錯(cuò)誤原因是先對(duì)list操作后，開啟翻頁后沒有sql語句

即sql語句沒有參與分頁查詢

3.解決方案

直接對(duì)分頁后的PageInfo對(duì)象中的數(shù)據(jù)進(jìn)行操作①對(duì)list集合操作，先取出PageInfo里的list集合數(shù)據(jù)，再對(duì)數(shù)據(jù)進(jìn)行相關(guān)操作②將操作完后的list集合再次存到PageInfo里，進(jìn)行return

@Override public PageInfo<HdQueryVo> getRecordsByView(int pageNo, int pageSize) {PageInfo<HdQueryVo> source = PageHelper.startPage(pageNo, pageSize).doSelectPageInfo(()->{ actionMapper.getActionByView();});// 需要轉(zhuǎn)換的對(duì)象PageInfo<HdQueryVo> target = new PageInfo<>();// 復(fù)制分頁屬性BeanUtils.copyProperties(source, target);// 對(duì)查詢的list進(jìn)行下一步操作，比如類型轉(zhuǎn)換后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);}// 加工后的數(shù)據(jù)放入新的pageinfotarget.setList(hdQueryVos);return target; }

參考資料：

PageHelper官方文檔PageHelper分頁查詢結(jié)果后再對(duì)數(shù)據(jù)List操作的方法

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