Day 13: Schedulers in AEM

AEM Developer Series

• Day 00: AEM Developer Series
• Day 01: Introduction to AEM
• Day 02: AEM Architecture
• Day 03: Setting up AEM Development Environment
• Day 04: Developing First OSGi Bundle
• Day 05: Working with Sling Servlets in AEM
• Day 06: Playing with Sling Post Servlet
• Day 07: Creating your first component in AEM
• Day 08: Dueling with JavaScript Use API
• Day 09: Dueling with Java Use API
• Day 10: Getting to know Sling Models
• Day 11: Client Libraries in Action
• Day 12: Creating your custom OSGi Configuration
• Day 13: Schedulers in AEM
• Day 14: Eventing in AEM
• Day 15: Custom Workflows in AEM
• Day 16: Creating JMX Beans in AEM
• Day 17: Working with QueryBuilder API
• Day 18: Working with Granite Datasources in AEM
• Day 19: Replication API in Action
• Day 20: Working with Users and Groups in AEM

In simple terms, a scheduler is a service to schedule jobs. Thus if we want some work to happen at a particular time or at a regular interval, then Schedulers are the way to go.

In AEM, we can create scheduler in two ways -

1. Whiteboard Pattern - In this, we create a Runnable thread to perform our task. This is similar to the Java Thread concept.
2. Scheduler API - In this, we use Apache Commons' Scheduler API to perform our task. It uses open-source Quartz library.

Both of these methods can be seen here. However, from AEM 6.2 onwards Felix SCR annotations are deprecated and are replaced with OSGi R6 annotations. Therefore, in this post, we will be discussing the clean way of creating schedulers that OSGi R6 annotations provide.

Scheduler in AEM

To create a scheduler in AEM, we will follow the below steps - 

• Create an OSGi configuration to read the scheduler specific values from the user i.e. cron expression, the name of the scheduler, custom parameter etc.
• Create a sling scheduler which displays the custom parameter at an interval specified by the cron expression.

Without making further delay, let's dive into our code

Create an OSGi configuration

Follow this post to create a new OSGi configuration class and paste the following code in it.

Here we are getting configuration properties for the Sling Scheduler.

Create Scheduler

Now we are going to create a sling scheduler. Create a class named CustomScheduler and paste the following code in it.

• Let us understand the code step-by-step. First, we are registering the class as a service and implementing the Runnable interface. At the same time, using @Desginate annotation, we are linking the OSGi configuration created in the previous section with this class.
• Now, we are injecting the org.apache.sling.commons.scheduler.Scheduler dependency.
• In the activate() method, we are reading the required values. Then we are getting the schedulerId from the scheduler name.
• The modified() method recalculates the schedulerId in case the OSGi configuration is modified.
• In the addScheduler() method, we are registering the scheduler using the Scheduler API.
• The run() method will be defining our task. Here we are just printing the customParameter in the logs.

Configuring OSGi

• Go to ./system/console/configMgr and search for SlingSchedulerConfiguration and configure it like below screenshot.

OSGi Configuration

• Save the configuration.

Result

Now go to your project-specific log (my log file is - project-demoproject.log) and look for the traces, you will find like below

org.redquark.demo.core.schedulers.CustomScheduler Scheduler added

org.redquark.demo.core.schedulers.CustomScheduler Custom Scheduler is now running using the passed custom parameter, customParameter AEM Scheduler Demo

org.redquark.demo.core.schedulers.CustomScheduler Custom Scheduler is now running using the passed custom parameter, customParameter AEM Scheduler Demo

org.redquark.demo.core.schedulers.CustomScheduler Removing scheduler: -1760311957

org.redquark.demo.core.schedulers.CustomScheduler Scheduler added

org.redquark.demo.core.schedulers.CustomScheduler Custom Scheduler is now running using the passed custom parameter, customParameter AEM Scheduler Demo

org.redquark.demo.core.schedulers.CustomScheduler Custom Scheduler is now running using the passed custom parameter, customParameter AEM Scheduler Demo

Conclusion

Congratulations!! 🙋 we have successfully created a Sling Scheduler and I hope you enjoyed this post.

You can find the complete code of this project on my GitHub in this commit. Feel free to fork or open issues, if any.

I would love to hear your thoughts on this and would like to have suggestions from you to make it better. 

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Happy Coding 😃