我每天凌晨5点都在尝试完成某项任务。所以我决定使用ScheduledExecutorService，但到目前为止，我已经看到了一些示例，显示了如何每隔几分钟运行一次任务。
我无法找到任何显示如何在早上的特定时间（早上5点）每天运行任务的例子，同时也考虑夏令时的事实 -
以下是我的代码，每15分钟运行一次 -
public class ScheduledTaskExample {
private final ScheduledExecutorService scheduler = Executors
.newScheduledThreadPool(1);
public void startScheduleTask() {
/**
* not using the taskHandle returned here, but it can be used to cancel
* the task, or check if it's done (for recurring tasks, that's not
* going to be very useful)
*/
final ScheduledFuture<?> taskHandle = scheduler.scheduleAtFixedRate(
new Runnable() {
public void run() {
try {
getDataFromDatabase();
}catch(Exception ex) {
ex.printStackTrace(); //or loggger would be better
}
}
}, 0, 15, TimeUnit.MINUTES);
}
private void getDataFromDatabase() {
System.out.println("getting data...");
}
public static void main(String[] args) {
ScheduledTaskExample ste = new ScheduledTaskExample();
ste.startScheduleTask();
}
}
有什么办法，考虑到夏令时这个事实，我可以安排一个任务每天凌晨5点用ScheduledExecutorService运行吗？
还有TimerTask对于这个还是ScheduledExecutorService更好？
与目前的Java SE 8发布一样，它具有java.time的优秀日期时间API，这种计算可以更容易地完成，而不是使用java.util.Calendar和java.util.Date。
现在作为使用您的用例计划任务的示例示例：
ZonedDateTime now = ZonedDateTime.now(ZoneId.of("America/Los_Angeles"));
ZonedDateTime nextRun = now.withHour(5).withMinute(0).withSecond(0);
if(now.compareTo(nextRun) > 0)
nextRun = nextRun.plusDays(1);
Duration duration = Duration.between(now, nextRun);
long initalDelay = duration.getSeconds();
ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
scheduler.scheduleAtFixedRate(new MyRunnableTask(),
initalDelay,
TimeUnit.DAYS.toSeconds(1),
TimeUnit.SECONDS);
计算initalDelay是为了要求调度程序延迟TimeUnit.SECONDS中的执行。对于此用例，单位毫秒及以下的时差问题似乎可以忽略不计。但是你仍然可以使用duration.toMillis()和TimeUnit.MILLISECONDS来处理调度计算，以毫秒为单位。
而TimerTask对于这个还是ScheduledExecutorService更好？
NO：ScheduledExecutorService似乎比TimerTask好。 StackOverflow has already an answer for you。
来自@PaddyD，
如果您希望在当地正确的时间运行，您仍然需要每年重启两次。 scheduleAtFixedRate不会削减它，除非你对全年相同的UTC时间感到满意。
事实并且@PaddyD已经给出了一个解决方法（给他+1），我提供了一个使用ScheduledExecutorService的Java8日期时间API的工作示例。 Using daemon thread is dangerous
class MyTaskExecutor
{
ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);
MyTask myTask;
volatile boolean isStopIssued;
public MyTaskExecutor(MyTask myTask$)
{
myTask = myTask$;
}
public void startExecutionAt(int targetHour, int targetMin, int targetSec)
{
Runnable taskWrapper = new Runnable(){
@Override
public void run()
{
myTask.execute();
startExecutionAt(targetHour, targetMin, targetSec);
}
};
long delay = computeNextDelay(targetHour, targetMin, targetSec);
executorService.schedule(taskWrapper, delay, TimeUnit.SECONDS);
}
private long computeNextDelay(int targetHour, int targetMin, int targetSec)
{
LocalDateTime localNow = LocalDateTime.now();
ZoneId currentZone = ZoneId.systemDefault();
ZonedDateTime zonedNow = ZonedDateTime.of(localNow, currentZone);
ZonedDateTime zonedNextTarget = zonedNow.withHour(targetHour).withMinute(targetMin).withSecond(targetSec);
if(zonedNow.compareTo(zonedNextTarget) > 0)
zonedNextTarget = zonedNextTarget.plusDays(1);
Duration duration = Duration.between(zonedNow, zonedNextTarget);
return duration.getSeconds();
}
public void stop()
{
executorService.shutdown();
try {
executorService.awaitTermination(1, TimeUnit.DAYS);
} catch (InterruptedException ex) {
Logger.getLogger(MyTaskExecutor.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
注意：
MyTask是功能execute的接口。ScheduledExecutorService时，总是在调用awaitTermination之后使用shutdown：总是有可能你的任务卡住/死锁，用户会永远等待。我之前使用Calendar的例子只是我提到的一个想法，我避免了精确的时间计算和夏令时问题。根据@PaddyD的投诉更新了解决方案
您可以使用以下课程每天特定时间安排您的任务
package interfaces;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;
import java.util.Date;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class CronDemo implements Runnable{
public static void main(String[] args) {
Long delayTime;
ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
final Long initialDelay = LocalDateTime.now().until(LocalDate.now().plusDays(1).atTime(12, 30), ChronoUnit.MINUTES);
if (initialDelay > TimeUnit.DAYS.toMinutes(1)) {
delayTime = LocalDateTime.now().until(LocalDate.now().atTime(12, 30), ChronoUnit.MINUTES);
} else {
delayTime = initialDelay;
}
scheduler.scheduleAtFixedRate(new CronDemo(), delayTime, TimeUnit.DAYS.toMinutes(1), TimeUnit.MINUTES);
}
@Override
public void run() {
System.out.println("I am your job executin at:" + new Date());
}
}
在Java 8中：
scheduler = Executors.newScheduledThreadPool(1);
//Change here for the hour you want ----------------------------------.at()
Long midnight=LocalDateTime.now().until(LocalDate.now().plusDays(1).atStartOfDay(), ChronoUnit.MINUTES);
scheduler.scheduleAtFixedRate(this, midnight, 1440, TimeUnit.MINUTES);
如果您没有能够使用Java 8的奢侈品，以下将满足您的需求：
public class DailyRunnerDaemon
{
private final Runnable dailyTask;
private final int hour;
private final int minute;
private final int second;
private final String runThreadName;
public DailyRunnerDaemon(Calendar timeOfDay, Runnable dailyTask, String runThreadName)
{
this.dailyTask = dailyTask;
this.hour = timeOfDay.get(Calendar.HOUR_OF_DAY);
this.minute = timeOfDay.get(Calendar.MINUTE);
this.second = timeOfDay.get(Calendar.SECOND);
this.runThreadName = runThreadName;
}
public void start()
{
startTimer();
}
private void startTimer();
{
new Timer(runThreadName, true).schedule(new TimerTask()
{
@Override
public void run()
{
dailyTask.run();
startTimer();
}
}, getNextRunTime());
}
private Date getNextRunTime()
{
Calendar startTime = Calendar.getInstance();
Calendar now = Calendar.getInstance();
startTime.set(Calendar.HOUR_OF_DAY, hour);
startTime.set(Calendar.MINUTE, minute);
startTime.set(Calendar.SECOND, second);
startTime.set(Calendar.MILLISECOND, 0);
if(startTime.before(now) || startTime.equals(now))
{
startTime.add(Calendar.DATE, 1);
}
return startTime.getTime();
}
}
它不需要任何外部库，并将占用夏令时。简单地传递您想要作为Calendar对象运行任务的时间，并将任务作为Runnable。例如：
Calendar timeOfDay = Calendar.getInstance();
timeOfDay.set(Calendar.HOUR_OF_DAY, 5);
timeOfDay.set(Calendar.MINUTE, 0);
timeOfDay.set(Calendar.SECOND, 0);
new DailyRunnerDaemon(timeOfDay, new Runnable()
{
@Override
public void run()
{
try
{
// call whatever your daily task is here
doHousekeeping();
}
catch(Exception e)
{
logger.error("An error occurred performing daily housekeeping", e);
}
}
}, "daily-housekeeping");
注：计时器任务在守护程序线程中运行，不建议执行任何IO。如果需要使用User线程，则需要添加另一个取消计时器的方法。
如果你必须使用ScheduledExecutorService，只需将startTimer方法更改为以下内容：
private void startTimer()
{
Executors.newSingleThreadExecutor().schedule(new Runnable()
{
Thread.currentThread().setName(runThreadName);
dailyTask.run();
startTimer();
}, getNextRunTime().getTime() - System.currentTimeMillis(),
TimeUnit.MILLISECONDS);
}
我不确定这种行为，但你可能需要一个停止方法，如果你沿着shutdownNow路线调用ScheduledExecutorService，否则当你试图阻止它时你的应用程序可能会挂起。
Java 8： 我的升级版本来自最佳答案：
/**
* Execute {@link AppWork} once per day.
* <p>
* Created by aalexeenka on 29.12.2016.
*/
public class OncePerDayAppWorkExecutor {
private static final Logger LOG = AppLoggerFactory.getScheduleLog(OncePerDayAppWorkExecutor.class);
private ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);
private final String name;
private final AppWork appWork;
private final int targetHour;
private final int targetMin;
private final int targetSec;
private volatile boolean isBusy = false;
private volatile ScheduledFuture<?> scheduledTask = null;
private AtomicInteger completedTasks = new AtomicInteger(0);
public OncePerDayAppWorkExecutor(
String name,
AppWork appWork,
int targetHour,
int targetMin,
int targetSec
) {
this.name = "Executor [" + name + "]";
this.appWork = appWork;
this.targetHour = targetHour;
this.targetMin = targetMin;
this.targetSec = targetSec;
}
public void start() {
scheduleNextTask(doTaskWork());
}
private Runnable doTaskWork() {
return () -> {
LOG.info(name + " [" + completedTasks.get() + "] start: " + minskDateTime());
try {
isBusy = true;
appWork.doWork();
LOG.info(name + " finish work in " + minskDateTime());
} catch (Exception ex) {
LOG.error(name + " throw exception in " + minskDateTime(), ex);
} finally {
isBusy = false;
}
scheduleNextTask(doTaskWork());
LOG.info(name + " [" + completedTasks.get() + "] finish: " + minskDateTime());
LOG.info(name + " completed tasks: " + completedTasks.incrementAndGet());
};
}
private void scheduleNextTask(Runnable task) {
LOG.info(name + " make schedule in " + minskDateTime());
long delay = computeNextDelay(targetHour, targetMin, targetSec);
LOG.info(name + " has delay in " + delay);
scheduledTask = executorService.schedule(task, delay, TimeUnit.SECONDS);
}
private static long computeNextDelay(int targetHour, int targetMin, int targetSec) {
ZonedDateTime zonedNow = minskDateTime();
ZonedDateTime zonedNextTarget = zonedNow.withHour(targetHour).withMinute(targetMin).withSecond(targetSec).withNano(0);
if (zonedNow.compareTo(zonedNextTarget) > 0) {
zonedNextTarget = zonedNextTarget.plusDays(1);
}
Duration duration = Duration.between(zonedNow, zonedNextTarget);
return duration.getSeconds();
}
public static ZonedDateTime minskDateTime() {
return ZonedDateTime.now(ZoneId.of("Europe/Minsk"));
}
public void stop() {
LOG.info(name + " is stopping.");
if (scheduledTask != null) {
scheduledTask.cancel(false);
}
executorService.shutdown();
LOG.info(name + " stopped.");
try {
LOG.info(name + " awaitTermination, start: isBusy [ " + isBusy + "]");
// wait one minute to termination if busy
if (isBusy) {
executorService.awaitTermination(1, TimeUnit.MINUTES);
}
} catch (InterruptedException ex) {
LOG.error(name + " awaitTermination exception", ex);
} finally {
LOG.info(name + " awaitTermination, finish");
}
}
}
你考虑过使用像Quartz Scheduler这样的东西吗？这个库有一个机制，用于使用类似cron的表达式来安排每天在设定的时间段内运行的任务（看看CronScheduleBuilder）。
一些示例代码（未测试）：
public class GetDatabaseJob implements InterruptableJob
{
public void execute(JobExecutionContext arg0) throws JobExecutionException
{
getFromDatabase();
}
}
public class Example
{
public static void main(String[] args)
{
JobDetails job = JobBuilder.newJob(GetDatabaseJob.class);
// Schedule to run at 5 AM every day
ScheduleBuilder scheduleBuilder =
CronScheduleBuilder.cronSchedule("0 0 5 * * ?");
Trigger trigger = TriggerBuilder.newTrigger().
withSchedule(scheduleBuilder).build();
Scheduler scheduler = StdSchedulerFactory.getDefaultScheduler();
scheduler.scheduleJob(job, trigger);
scheduler.start();
}
}
预先有一些工作，你可能需要重写你的工作执行代码，但它应该让你更好地控制你希望你的工作运行方式。如果需要，也可以更容易地更改计划。
我遇到了类似的问题。我不得不安排一天中应该使用ScheduledExecutorService执行的一堆任务。这是通过一个任务从凌晨3:30开始解决所有其他任务相对于他当前时间来解决的。并在第二天凌晨3:30重新安排自己。
在这种情况下，夏令时不再是问题。
您可以使用简单的日期解析，如果当天的时间是现在之前，那么我们明天就开始：
String timeToStart = "12:17:30";
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd 'at' HH:mm:ss");
SimpleDateFormat formatOnlyDay = new SimpleDateFormat("yyyy-MM-dd");
Date now = new Date();
Date dateToStart = format.parse(formatOnlyDay.format(now) + " at " + timeToStart);
long diff = dateToStart.getTime() - now.getTime();
if (diff < 0) {
// tomorrow
Date tomorrow = new Date();
Calendar c = Calendar.getInstance();
c.setTime(tomorrow);
c.add(Calendar.DATE, 1);
tomorrow = c.getTime();
dateToStart = format.parse(formatOnlyDay.format(tomorrow) + " at " + timeToStart);
diff = dateToStart.getTime() - now.getTime();
}
ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
scheduler.scheduleAtFixedRate(new MyRunnableTask(), TimeUnit.MILLISECONDS.toSeconds(diff) ,
24*60*60, TimeUnit.SECONDS);
只是加起来Victor's answer。
如果变量（在他的情况下是长midnight）高于1440，我建议添加一个检查。如果是的话，我会省略.plusDays(1)，否则任务只会在后天运行。
我这么做是这样的：
Long time;
final Long tempTime = LocalDateTime.now().until(LocalDate.now().plusDays(1).atTime(7, 0), ChronoUnit.MINUTES);
if (tempTime > 1440) {
time = LocalDateTime.now().until(LocalDate.now().atTime(7, 0), ChronoUnit.MINUTES);
} else {
time = tempTime;
}
以下示例适用于我
public class DemoScheduler {
public static void main(String[] args) {
// Create a calendar instance
Calendar calendar = Calendar.getInstance();
// Set time of execution. Here, we have to run every day 4:20 PM; so,
// setting all parameters.
calendar.set(Calendar.HOUR, 8);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.AM_PM, Calendar.AM);
Long currentTime = new Date().getTime();
// Check if current time is greater than our calendar's time. If So,
// then change date to one day plus. As the time already pass for
// execution.
if (calendar.getTime().getTime() < currentTime) {
calendar.add(Calendar.DATE, 1);
}
// Calendar is scheduled for future; so, it's time is higher than
// current time.
long startScheduler = calendar.getTime().getTime() - currentTime;
// Setting stop scheduler at 4:21 PM. Over here, we are using current
// calendar's object; so, date and AM_PM is not needed to set
calendar.set(Calendar.HOUR, 5);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.AM_PM, Calendar.PM);
// Calculation stop scheduler
long stopScheduler = calendar.getTime().getTime() - currentTime;
// Executor is Runnable. The code which you want to run periodically.
Runnable task = new Runnable() {
@Override
public void run() {
System.out.println("test");
}
};
// Get an instance of scheduler
final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
// execute scheduler at fixed time.
scheduler.scheduleAtFixedRate(task, startScheduler, stopScheduler, MILLISECONDS);
}
}
参考：https://chynten.wordpress.com/2016/06/03/java-scheduler-to-run-every-day-on-specific-time/