java stream操作案例

1、从List<Staff>筛选符合条件的List<String>：

List<Staff> staffListtemp=Lists.newArrayList();
List<String> staffIdList=staffListtemp.stream().filter(staff->deptIdSet.contains(staff.getDeptId())).map(staffId->staffId.getStaffId()).collect(Collectors.toList());

2、从List<PositionRealtime>转为Map<String,PositionRealtime>：

List<PositionRealtime> prList
Map<String,PositionRealtime> prMap=prList.stream().collect(Collectors.toMap(PositionRealtime::getStaffId, PositionRealtime->PositionRealtime));

3、从Set<String>转为拼接后的String：

Set<String> inPostStaffIds = Sets.newHashSet();
String inPostIds = inPostStaffIds.stream().reduce((a,b)->a+","+b).get();

4、从List<StaffGpsTimeDTO>通过StaffId作为分组条件分组为Map<String,List<StaffGpsTimeDTO>>对象：

List<StaffGpsTimeDTO> positionHistoryTimeList = positionHistoryManageDao.getPositionHistoryTimeList(filterPropertyMap2);
for(StaffGpsTimeDTO staffGpsTimeDTO : positionHistoryTimeList){
    List<Date> list = Lists.newArrayList();
    if(gpsMap.get(staffGpsTimeDTO.getStaffId()) != null){
        list = gpsMap.get(staffGpsTimeDTO.getStaffId());
    }
    list.add(staffGpsTimeDTO.getGpsTime());
    gpsMap.put(staffGpsTimeDTO.getStaffId(), list);
}
Map<string,List<>> aaa=positionHistoryTimeList.stream().collect(Collectors.groupingBy(StaffGpsTimeDTO::getStaffId,Collectors.mapping(StaffGpsTimeDTO::getGpsTime, Collectors.toList())));

原文地址：http://blog.51cto.com/481814/2163215