How to convert CRON string to ScheduleExpression i

Question

I got this problem:

I have a text field,

There should be a CRON expression written, and later on saved.

Now I need a method to convert the CRON string (here are some random examples: http://www.quartz-scheduler.org/documentation/quartz-2.x/tutorials/crontrigger.html) to java ScheduleExpression (http://docs.oracle.com/javaee/6/api/javax/ejb/ScheduleExpression.html)

But, I have no idea how to do it...

I have a timer based execution system, that run only on days, weeks and months, but now I need to implement the CRON models, so that the executions can be run on a specific period of time...

here is a little code, just to back me up:

@Resource
private TimerService timerService;


@Timeout
public void execute(Timer timer) {
    Script s = (Script) timer.getInfo();
    execute(s, true);
    System.out.println("Timer Service : " + s.getScriptId());
    System.out.println("Current Time : " + new Date());
    System.out.println("Next Timeout : " + timer.getNextTimeout());
    System.out.println("Time Remaining : " + timer.getTimeRemaining());
    System.out.println("____________________________________________");
    Date today = new Date();
    if (s.getTimerSetup().getEndDate() <= today.getTime()) {
        stopTimer(s);
    }
}


@Override
public void startTimer(Script s) {
    if (s.getTimerSetup().getTimerRepeat().equals("0")) {
        return;
    }
    s.setStatus(true);
    em.merge(s);
    em.flush();
    if (s.getTimerSetup().getEndDate() > System.currentTimeMillis()) {
        long timeOut = 1L;
        String timerRepeat = s.getTimerSetup().getTimerRepeat();

        if (timerRepeat.equals("1")) {// day
            timeOut = 1000L * 60L * 60L * 24L;
        } else if (timerRepeat.equals("2")) {// week
            timeOut = 1000L * 60L * 60L * 24L * 7L;
        } else if (timerRepeat.equals("3")) {// month
            timeOut = 1000L * 60L * 60L * 24L * 30L;
        } else {
            return; //Here is the part where the cron string is detected
        }

        long initialTimeOut = s.getTimerSetup().getStartDate() - System.currentTimeMillis();

        if (initialTimeOut < 0) {
            long initCheck = initialTimeOut * -1;
            while (initCheck > timeOut) {
                initCheck -= timeOut;
            }
            initialTimeOut = timeOut - initCheck;
        }

        Boolean found = false;
        if (timerService.getAllTimers().size() == 0) {
            System.out.println("Started the timer for the script: " + s.getFileName());
            timerService.createTimer(initialTimeOut, timeOut, s);
        } else {
            for (Timer timer : timerService.getAllTimers()) {
                if (((Script) timer.getInfo()).getScriptId() == s.getScriptId()) {
                    System.out.println("This script's timer was already started!");
                    found = true;
                }
            }

            if (!found) {
                System.out.println("Started the timer for the script: " + s.getFileName());
                timerService.createTimer(initialTimeOut, timeOut, s);
                found = true;
            }
        }
    } else {
        System.out.println("The script's end date has expired");
    }
}

I marked the place where the cron string is detected (in the if statement) And I need now to transform the string to a ScheduleExpression.

And after that to run it with the normal timers. (but that comes later :))

Please help. Thanks in advance.

Answer 1

I found the answer, but forgot to answer it, here is the code that worked for me:

private ScheduleExpression parseCronExpressionToScheduleExpression(String cronExpression) {

    if ("never".equals(cronExpression)) {
        return null;
    }

    // parsing it more or less like cron does, at least supporting same fields (+ seconds)

    final String[] parts = cronExpression.split(" ");
    final ScheduleExpression scheduleExpression;

    if (parts.length != 6 && parts.length != 5) {
        scheduleExpression = scheduleAliases.get(cronExpression);
        if (scheduleExpression == null) {
            throw new IllegalArgumentException(cronExpression + " doesn't have 5 or 6 segments as excepted");
        }
        return scheduleExpression;
    } else if (parts.length == 6) { // enriched cron with seconds
        return new ScheduleExpression()
                .second(parts[0])
                .minute(parts[1])
                .hour(parts[2])
                .dayOfMonth(parts[3])
                .month(parts[4])
                .dayOfWeek(parts[5]);
    }

    // cron
    return new ScheduleExpression()
            .minute(parts[0])
            .hour(parts[1])
            .dayOfMonth(parts[2])
            .month(parts[3])
            .dayOfWeek(parts[4]);
}

So, if you send the cron expression to the function, it will make a shedule expression out of it, but it does not work 100% on all cron expressions but on most

Here is what worked for the individual positions in the cron expression

*    works 
-    works
,    works
/    works
last works (only in the part Day Of Month)

What does not work are the letters, such as L, and the others, at least not when I last checked.

Hope this will help the next guy :)