How to i invoke a method every 24 hours

[Aditya Sirohi]

Hi Folks

I have to invoke a method after every 24 hours, how do i do it. I will get the last invoke time for this method from the repository and if the current system time is greater than 24 hours, this method will be invoked. Do i need threads or there is some other class like cron jobs in Unix i can implement?

Thanks
Adi

[Ralph Cook]

There is no cron-type scheduler in standard Java that I know of.

You can store the time the methodwas last invoked, and then compare that time to the current time; I would myself store and compare the time as a long of milliseconds, I think it just makes it easier. Then see if the difference is greater than 24*60*60*1000.

You only need thread if you have some independent bit of computing you want done while other things are going on. If you have a long-running method, for instance, and want to have something else done every 24 hours regardless of what it is doing, then you could have a thread computed how long it should have to wait from being started before it should wake up and execute, and then do a Thread.sleep() for that long, execute and repeat. So whether you need a thread depends on what else your program is doing.

rc

[Hauke Ingmar Schmidt]

If you use Quartz Scheduler you can use a cron-like trigger.

[Deep Purohit]

As per what I understood, you want to run a task every 24 hours.
If you use inbuilt java scheduling, you don't need to store the time in repository. It will automatically do the job for you.

In essence, the "java scheduler = TimerTask + Timer;"
'TimeTask' is an abstract class which you extend in the class which does the processing.
'Timer' is the class which you will use in your scheduler class.

I just made a sample example for you to check:

Processing class

 
public class ProcessingClass extends TimerTask{
	public void run() {
		System.out.println("The task is called " + new Date());
	}
}

Scheduler class

public class Scheduler {
	public static void main(String[] args) {
		Timer timer = new Timer();
		Calendar date = Calendar.getInstance();
		//Setting the date from when you want to activate scheduling
		date.set(2011, 3, 28, 21, 28);
		//execute every 3 seconds
		timer.schedule(new ProcessingClass(), date.getTime(), 3000);
	}
}

Here you can make changes in the execution from 3 seconds to 24 hours.

the other option is Quartz scheduling: An open source API for scheduling, provides more features.

[Aditya Sirohi]

Thanks Guys

[Michael Cropper]

Following on from this thread, as I am looking to do the exact same thing.

Just have one question from the information posted by Deep Purohit which is, how would this class be called?

Quartz seems like a full solution, but may be overly complex to setup for my requirements.

Thanks
Michael

[Wouter Oet]

The run method will be invoked by the Timer.

[Michael Cropper]

I have just set up the two example classes in my development environment and nothing is happening.

Not sure where I am going wrong here? As based on the explanations this should all work correctly since the class is called by the TimerTask automatically....but this doesn't seem to be working?

Edit:
What I have had to do to get the above working is to initialise and call the Scheduler class from another class that has been accessed. Which is kind of defeating the point of having a scheduler (using this method).

Based on this, am I correct in saying that the only way to create some kind of cron job (similar principal) is to use Quartz? As I want the job to run totally independent of anything else, except the system clock.

Thanks
Michael

[Wouter Oet]

Try something like this:

Timer timer = new Timer();
TimerTask task = new TimerTask() {
	@Override
	public void run() {
		System.out.println("Whoot");
	}
};
timer.schedule(task, 0, 300);

Thread.sleep(100000);

[Michael Cropper]

Not quite sure which of the two files that would go into? As it appears to be doing a similar task (from a single file though) - which would still encounter the same issue of the class having to be called in the first place.

Tried adding the script into both files (one at a time) and the only way it would work was if I called the class from another class that was being run manually, which defeats the whole point.

Thanks
Michael

[Wouter Oet]

I wrote that code before you edited your post but a different parts belong in different files.

Creating a Scheduler class is not defeating the point. That way you can hide how you implemented it.
So no creating something like a cron job isn't only possible using Quartz.

[Michael Cropper]

Can you be a little more descriptive on how this works please, as I am still not understanding how this works behind the scenes. (or point me in the direction of some reading so I will understand this more).

Incidentally I have found another solution to what I required, but I would still like to understand what has been discussed as I will no doubt need this at some point in the future.

Thanks
Michael

[Wouter Oet]

If you write a Scheduler class which allows the application to schedule events then that hides the implementation details.
Internally you could use Quartz of java.util.Timer or write something yourself. That isn't visible for the application.