CronScheduler

Basic cron scheduler which can be used in different cases.

Purpose

Kafka connect usually works by using streams or when it's not possible, it tries to poll at a very short interval.

In some cases we would like to not start the replication right away and have a little space between each runs. Either because the process is CPU intensive, the other system has a rate limit, or we're paying per request to the other system.

This library helps us to solve these problems.

Diagram

Cron expression

Take care, all expressions must be declared as Quartz expressions.

The following example expression allows an execution every five minutes.

0 0/5 * * * ?

Implementation

This is a very basic implementation example.

// Create scheduler
final CronScheduler scheduler = new CronScheduler("0 0/5 * * * ?");

// will be executed very often
public List<Object> poll() {
    if(scheduler.checkIfExecutionIsAllowed()) {
        final List<Object> data = getData();
        
        if(data.isEmpty()) {
            scheduler.moveToNextTimeSlot();
            return emptyList();
        }

        return data;
    }

    scheduler.waitUntilNextExecutionIsAllowed();
    return emptyList();
}

public void stop() {
    scheduler.stop();
}

Development and testing

To build and test this lib run: