Develop Reference

how to calculate initialDelay for ScheduledExecutorService#scheduleAtFixedRate

I want to run a task at a specific time say at 7.11pm everyday.
I have tried the following piece of code but it is not working.
import java.util.Calendar;
import java.util.Date;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class Task3 {
public static void main(String[] args) {
Runnable runnable = new Runnable() {
public void run() {
System.out.println(new Date());
System.out.println("Hello !!");
}
};
Calendar calendar = Calendar.getInstance();
long now = calendar.getTimeInMillis();
calendar.set(Calendar.HOUR, 18);
calendar.set(Calendar.MINUTE, 11);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);
ScheduledExecutorService service = Executors.newSingleThreadScheduledExecutor();
service.scheduleAtFixedRate(runnable, calendar.getTimeInMillis(), 5, TimeUnit.SECONDS);
}
}
In the above code, I have tried to run the schedule task starting from 7:11pm everyday with an interval of 5 seconds. But it is not behaving as I expected to be. And also If I want to do the same with another condition that the task should be executed only on specific days let's say every Tuesday and Wednesday.
Am I making some kind of mistake in calculating the initialDelay parameter of the method or something else?

Side comment: it would probably be simpler to use an ad hoc library (such as quartz).
The initialDelay parameter gives the number of time unit to wait before running the task. In your case, you need to calculate the time left to 7:11.
So it could look like:
long nextRun = calendar.getTimeInMillis();
long initialDelayMillis = nextRun - now;
long oneDayMillis = 1000L * 60 * 60 * 24;
service.scheduleAtFixedRate(runnable, initialDelayMillis, oneDayMillis, TimeUnit.MILLISECONDS);
but this will only handle basic situations. In particular it won't handle clock adjustments or DST at all. And it won't be easy to say "only on Tuesdays and Wendesdays".
An alternative would be to only schedule the next run and reschedule it at the end of the runnable. That way you can have a finer control on the execution. But bottom line is: see my initial comment.

Preferable would be the scheduledExecutorService.
But maybe timer could be used too. For swing the other timer.
Here an example (the timer and timerTask could be stoped with cancel/purge).
import java.util.Calendar;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
public class TimeScheduleTest {
Timer timer = new Timer();
public static void main(String[] args) {
new TimeScheduleTest().startApp();
}
private void startApp() {
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.DAY_OF_WEEK,Calendar.TUESDAY);
calendar.set(Calendar.HOUR_OF_DAY, 7);
calendar.set(Calendar.MINUTE, 11);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);
timer.scheduleAtFixedRate(new StartTimer(), calendar.getTime(), 5000);
}
class StartTimer extends TimerTask {
public void run() {
System.out.println(new Date());
System.out.println("Hello !!");
}
}
}

Java TimerTask - Run a task at XX:MM hours everyday

Using Timer and TimerTask.
Not able to understand why is this configuration starting the task immediately on deployment (using this in a web based Spring app). It should be started at today.getTime and then must repeat every day.
Calendar today = Calendar.getInstance();
today.set(Calendar.HOUR_OF_DAY, 3);
today.set(Calendar.MINUTE, 0);
today.set(Calendar.SECOND, 0);
MyTask task = new MyTask();
Timer timerJob = new Timer();
timerJob.schedule(task, today.getTime(),
TimeUnit.MILLISECONDS.convert(1, TimeUnit.DAYS));

I think, it would be better to use CronTrigger or Trigger with 24hours repeat interval.
Example of CronTrigger:
public class CronTriggerRunner {
public static void main(String args[]) throws SchedulerException, Exception {
SchedulerFactory schedulerFactory = new StdSchedulerFactory();
Scheduler scheduler = schedulerFactory.getScheduler();
JobDetail job = JobBuilder.newJob(ClassToRun.class).withIdentity("jobName", "group").build();
// Starting CronTrigger
String exp = "0 0 9 * * ?"; //trigger format, everyday at 9:00 am
Trigger trigger = TriggerBuilder.newTrigger()
.startNow()
.withSchedule(
CronScheduleBuilder.cronSchedule(exp))
.build();
// Planning job detail
scheduler.scheduleJob(job, trigger);
// starting scheduler
scheduler.start();
}
}
ClassToRun.java
public class ClassToRun implements Job {
#Override
public void execute(JobExecutionContext context) throws JobExecutionException {
try{
//doSomething
}
catch(Exception e){
e.printStackTrace(System.out);
}
}
}
Everyday at 9:00 am, public void execute() function will doSomething :D
Hope this will help. Please let me know.
EDIT: You need to download and add 2 jar files. 1) quartz-2.2.1.jar 2) slf4j-api-1.6.6.jar

How to set the time?

suppose i want to start the execution of the thread at some specific time,at time which i want,how can i set the time in below code so that i can start the thread at specific time and after that same thread will keep executing after given interval of time.
(in sample code ,suppose i want to start the beeper at midnight,how can i do that?
class BeeperControl {
private final ScheduledExecutorService scheduler =
Executors.newScheduledThreadPool(1);
public void beepForAnHour() {
final Runnable beeper = new Runnable() {
public void run() { System.out.println("beep"); }
};
final ScheduledFuture<?> beeperHandle =
scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
scheduler.schedule(new Runnable() {
public void run() { beeperHandle.cancel(true); }
}, 60 * 60, SECONDS);
}
}
Thanks in advance.

Look into Timer and TimerTask classes.
For advanced scheduling needs, look into Quartz job scheduler.

If you want to run the beeper after midnight, you need to change the initialDelay that you pass into the scheduler. Work out how much delay you need by subtracting the current time from midnight. This is shown below:
private static Date getMidnight(){
Calendar cal = new GregorianCalendar();
cal.add(Calendar.DAY_OF_MONTH,1);
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);
return cal.getTime();
}
long initialDelay = (getMidnight().getTime() - System.currentTimeMillis())/1000;
final ScheduledFuture<?> beeperHandle = scheduler.scheduleAtFixedRate(beeper, initialDelay, 10, SECONDS);

Initially schedule it by checking the difference between the current time and when you want to run the task. Then use the scheduleAtFixedRate..
However be warned, the thread need not be scheduled at the exact time you need it..

Java Timer

I'm trying to use a timer to schedule a recurring event in an application. However, I want to be able to adjust the period at which the event fires in real time (according to the users input).
For example:
public class HelperTimer extends TimerTask
{
private Timer timer;
//Default of 15 second between updates
private int secondsToDelay = 15;
public void setPeriod(int seconds)
{
this.secondsToDelay = seconds;
long delay = 1000; // 1 second
long period = 1000*secondsToDelay; // seconds
if (timer != null)
{
timer.cancel();
}
System.out.println(timer);
timer = new Timer();
System.out.println(timer);
timer.schedule(this, delay, period);
}
public int getPeriod()
{
return this.secondsToDelay;
}
}
I then start a new instance of this class and call its set period function. However, when I do that, I get an Illegal state exception. You can see the System.out.println(timer); in there because I'm checking, and yep sure enough, they are two different timers... so why am I getting an IllegalStateException when I try to run a schedule call on a brand new Timer instance!?!?!?!
java.util.Timer#c55e36
java.util.Timer#9664a1
Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException: Task already scheduled or cancelled
at java.util.Timer.sched(Unknown Source)
at java.util.Timer.schedule(Unknown Source)
at HelperTimer.setPeriod(HelperTimer.java:38)

You can't reuse a TimerTask as you're doing here.
Relevant porition of Timer:
private void sched(TimerTask task, long time, long period) {
if (time < 0)
throw new IllegalArgumentException("Illegal execution time.");
synchronized(queue) {
if (!thread.newTasksMayBeScheduled)
throw new IllegalStateException("Timer already cancelled.");
synchronized(task.lock) {
//Right here's your problem.
// state is package-private, declared in TimerTask
if (task.state != TimerTask.VIRGIN)
throw new IllegalStateException(
"Task already scheduled or cancelled");
task.nextExecutionTime = time;
task.period = period;
task.state = TimerTask.SCHEDULED;
}
queue.add(task);
if (queue.getMin() == task)
queue.notify();
}
}
You'll need to refactor your code so that you create a new TimerTask, rather than re-using one.

It seems odd to me to have a TimerTask with its own Timer inside it. Bad design. I'd totally separate the two and have the TimerTask implementation be handed off to a Timer, and put all that logic about fiddling with the period inside another class that provides an interface for doing so. Let that class instantiate the Timer and TimerTask and send them off to do their work.

You can use ScheduledExecutorService, which allows you to schedule the same task multiple times without using scheduleAtFixedRate. Here's a quick example:
ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);
Runnable timerTask = new Runnable() {
#Override
public void run() {
// Do something
System.out.println("Task run!");
// Schedule again
executorService.schedule(this, 15, TimeUnit.SECONDS);
}
};
// Schedule
executorService.schedule(timerTask, 15, TimeUnit.SECONDS);

In this exmaple, "Executed...." will be printed after 4 seconds of delay. After that, it will be printed continuously every 3 seconds:
import java.util.*;
class TimeSetting {
public static void main(String[] args) {
Timer t = new Timer();
TimerTask time = new TimerTask() {
public void run() {
System.out.println("Executed......");
}
};
t.scheduleAtFixedRate(time, 4000, 3000);
/*
* The task will be started after 4 secs and
* for every 3 seconds the task will be continuously
* executed.....
*/
}
}

Resettable Java Timer

I'd like to have a java.utils.Timer with a resettable time in java.I need to set a once off event to occur in X seconds. If nothing happens in between the time the timer was created and X seconds, then the event occurs as normal.
If, however, before X seconds has elapsed, I decide that the event should occur after Y seconds instead, then I want to be able to tell the timer to reset its time so that the event occurs in Y seconds.
E.g. the timer should be able to do something like:
Timer timer = new Timer();
timer.schedule(timerTask, 5000); //Timer starts in 5000 ms (X)
//At some point between 0 and 5000 ms...
setNewTime(timer, 8000); //timerTask will fire in 8000ms from NOW (Y).
I don't see a way to do this using the utils timer, as if you call cancel() you cannot schedule it again.
The only way I've come close to replicating this behavior is by using javax.swing.Timer and involves stopping the origional timer, and creating a new one. i.e.:
timer.stop();
timer = new Timer(8000, ActionListener);
timer.start();
Is there an easier way??

According to the Timer documentation, in Java 1.5 onwards, you should prefer the ScheduledThreadPoolExecutor instead. (You may like to create this executor using Executors.newSingleThreadScheduledExecutor() for ease of use; it creates something much like a Timer.)
The cool thing is, when you schedule a task (by calling schedule()), it returns a ScheduledFuture object. You can use this to cancel the scheduled task. You're then free to submit a new task with a different triggering time.
ETA: The Timer documentation linked to doesn't say anything about ScheduledThreadPoolExecutor, however the OpenJDK version had this to say:
Java 5.0 introduced the java.util.concurrent package and
one of the concurrency utilities therein is the
ScheduledThreadPoolExecutor which is a thread pool for repeatedly
executing tasks at a given rate or delay. It is effectively a more
versatile replacement for the Timer/TimerTask
combination, as it allows multiple service threads, accepts various
time units, and doesn't require subclassing TimerTask (just
implement Runnable). Configuring
ScheduledThreadPoolExecutor with one thread makes it equivalent to
Timer.

If your Timer is only ever going to have one task to execute then I would suggest subclassing it:
import java.util.Timer;
import java.util.TimerTask;
public class ReschedulableTimer extends Timer
{
private Runnable task;
private TimerTask timerTask;
public void schedule(Runnable runnable, long delay)
{
task = runnable;
timerTask = new TimerTask()
{
#Override
public void run()
{
task.run();
}
};
this.schedule(timerTask, delay);
}
public void reschedule(long delay)
{
timerTask.cancel();
timerTask = new TimerTask()
{
#Override
public void run()
{
task.run();
}
};
this.schedule(timerTask, delay);
}
}
You will need to work on the code to add checks for mis-use, but it should achieve what you want. The ScheduledThreadPoolExecutor does not seem to have built in support for rescheduling existing tasks either, but a similar approach should work there as well.

The whole Code snippet goes like this .... I hope it will be help full
{
Runnable r = new ScheduleTask();
ReschedulableTimer rescheduleTimer = new ReschedulableTimer();
rescheduleTimer.schedule(r, 10*1000);
public class ScheduleTask implements Runnable {
public void run() {
//Do schecule task
}
}
class ReschedulableTimer extends Timer {
private Runnable task;
private TimerTask timerTask;
public void schedule(Runnable runnable, long delay) {
task = runnable;
timerTask = new TimerTask() {
public void run() {
task.run();
}
};
timer.schedule(timerTask, delay);
}
public void reschedule(long delay) {
System.out.println("rescheduling after seconds "+delay);
timerTask.cancel();
timerTask = new TimerTask() {
public void run() {
task.run();
}
};
timer.schedule(timerTask, delay);
}
}
}

Do you need to schedule a recurring task? In that case I recommend you consider using Quartz.

I don't think it's possible to do it with Timer/TimerTask, but depending on what exactly you want to achieve you might be happy with using java.util.concurrent.ScheduledThreadPoolExecutor.

this is what I'm trying out. I have a class that polls a database every 60 seconds using a TimerTask.
in my main class, I keep the instance of the Timer, and an instance of my local subclass of TimerTask. the main class has a method to set the polling interval (say going from 60 to 30). in it, i cancel my TimerTask (which is my subclass, where I overwrote the cancel() method to do some cleanup, but that shouldn't matter) and then make it null. i recreate a new instance of it, and schedule the new instance at the new interval in the existing Timer.
since the Timer itself isn't canceled, the thread it was using stays active (and so would any other TimerTasks inside it), and the old TimerTask is replaced with a new one, which happens to be the same, but VIRGIN (since the old one would have been executed or scheduled, it is no longer VIRGIN, as required for scheduling).
when i want to shutdown the entire timer, i cancel and null the TimerTask (same as i did when changing the timing, again, for cleaning up resources in my subclass of TimerTask), and then i cancel and null the Timer itself.

Here is the example for Resetable Timer . Try to change it for your convinence...
package com.tps.ProjectTasks.TimeThread;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
/**
* Simple demo that uses java.util.Timer to schedule a task to execute
* every 5 seconds and have a delay if you give any input in console.
*/
public class DateThreadSheduler extends Thread {
Timer timer;
BufferedReader br ;
String data = null;
Date dNow ;
SimpleDateFormat ft;
public DateThreadSheduler() {
timer = new Timer();
timer.schedule(new RemindTask(), 0, 5*1000);
br = new BufferedReader(new InputStreamReader(System.in));
start();
}
public void run(){
while(true){
try {
data =br.readLine();
if(data != null && !data.trim().equals("") ){
timer.cancel();
timer = new Timer();
dNow = new Date( );
ft = new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz");
System.out.println("Modified Current Date ------> " + ft.format(dNow));
timer.schedule(new RemindTask(), 5*1000 , 5*1000);
}
}catch (IOException e) {
e.printStackTrace();
}
}
}
public static void main(String args[]) {
System.out.format("Printint the time and date was started...\n");
new DateThreadSheduler();
}
}
class RemindTask extends TimerTask {
Date dNow ;
SimpleDateFormat ft;
public void run() {
dNow = new Date();
ft = new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz");
System.out.println("Current Date: " + ft.format(dNow));
}
}
This example prints the current date and time for every 5 seconds...But if you give any input in console the timer will be delayed to perform the given input task...

I made an own timer class for a similar purpose; feel free to use it:
public class ReschedulableTimer extends Timer {
private Runnable mTask;
private TimerTask mTimerTask;
public ReschedulableTimer(Runnable runnable) {
this.mTask = runnable;
}
public void schedule(long delay) {
if (mTimerTask != null)
mTimerTask.cancel();
mTimerTask = new TimerTask() {
#Override
public void run() {
mTask.run();
}
};
this.schedule(mTimerTask, delay);
}
}