Java中PageHelper分頁后對list操作導致分頁無效

目錄1.問題1.1.PageHelper先開啟分頁，后對list數據操作1.2.先對list數據進行操作，后開啟分頁2.原因3.解決方案1.問題

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1.1.PageHelper先開啟分頁，后對list數據操作

@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，但是數據量錯誤，total始終等于每頁數據量，即pageSize

1.2.先對list數據進行操作，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; }

數據可以查詢出來，總數total也正確，但是分頁功能失效

2.原因

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

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

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

只是把list轉為PageInfo對象，不影響前面分頁數據的操作

1.2 錯誤原因是先對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

直接對分頁后的PageInfo對象中的數據進行操作①對list集合操作，先取出PageInfo里的list集合數據，再對數據進行相關操作②將操作完后的list集合再次存到PageInfo里，進行return

@Override public PageInfo<HdQueryVo> getRecordsByView(int pageNo, int pageSize) {PageInfo<HdQueryVo> source = PageHelper.startPage(pageNo, pageSize).doSelectPageInfo(()->{ actionMapper.getActionByView();});// 需要轉換的對象PageInfo<HdQueryVo> target = new PageInfo<>();// 復制分頁屬性BeanUtils.copyProperties(source, target);// 對查詢的list進行下一步操作，比如類型轉換后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);}// 加工后的數據放入新的pageinfotarget.setList(hdQueryVos);return target; }

參考資料：

PageHelper官方文檔PageHelper分頁查詢結果后再對數據List操作的方法

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