Java8 stream 常用写法

1.取List内对象的某个字段组装成List

List dateList = groupChart.stream().map(EmpWorkEfficiencyGroupDTO::getWorkDate).collect(Collectors.toList());

// 按固定规则处理并过滤 List --> List

list = list.stream().map(StringUtils::trim).filter(e -> !e.equals("")).collect(Collectors.toList());

2.按List对象内的某个字段分组进行统计

Map result = temporaryWorkers.stream().collect(Collectors.groupingBy(TemporaryWorker::getType, Collectors.counting()));

3.List转Map，方便用某个值直接拿到对象信息

Map dbMsgMap = dbMsgList.stream().collect(Collectors.toMap(e->e.getCode() + " " + e.getDate(), Function.identity(),(v1,v2)->v2));

4.按条件过滤后取部分值返回

List> tempList = groups.stream().filter(e-> EnumConstant.StatusEnum.ENABLE.getValue().equals(e.getStatus())).map((group) -> {
    Map map = new HashMap<>();
    map.put("code", group.getCode());
    map.put("name", group.getName());
    return map;
}).collect(Collectors.toList());

5.排序

List workers = workerList.stream().sorted(Comparator.comparing(TemporaryWorker::getId).reversed()).collect(Collectors.toList());

6.转字符串

String idsStr = companyIdList.stream().map(String::valueOf).collect(Collectors.joining(","));

7.并发处理

settleLogList.parallelStream().forEach(settleLog -> {
    //处理新插入处理
    CompanyManage companyManage = manageMap.get(settleLog.getCompanyId());
    if (Objects.nonNull(companyManage)) {
        settleLog.setCompanyName(companyManage.getShortName());
    }
});

8.按多个字段分组，返回Map

Map> listMap = employeeAttendanceList.stream().collect(Collectors.groupingBy(x -> MessageFormat.format("{0}-{1}", x.getCode(), x.getWorkDate())));

9.取最大值

LocalDateTime time = logs.stream().max(Comparator.comparing(DailyAttendancevalidLog::getCheckTime)).map(DailyAttendancevalidLog::getCheckTime).orElse(null);

10.对某个字段求和

int sum = otherList.stream().mapToInt(HrEnpEntryDepartureVO::getNum).sum();