Set OSGi Component properties dynamically using OCD - Use case with Sling ResourceChangeListener

This post demonstrates the use of Object Class Definition(OCD) in setting the OSGi component properties.


In general, per OSGi R6 annotations and above, we can set OSGi component properties via

  • property attribute of @Component annotation (Static values) or
  • Dynamically using @ObjectClassDefinition together with @AttributeDefinition  (property amends in run time via Config Admin or /system/console/configMgr)
    • AttributeDefinition should be framed such that it evaluates to the property name correctly (underscores are converted to dots/period)
    • Association of OCD with OSGi component happens via annotation named @Designate

Example : Component properties like service.ranking and in case of specific implementations like say WorkflowProcess, we set property named process.label and for EventHandler, it is EventConstants.EVENT_TOPIC and examples add on in a similar fashion for any OSGi Component for that matter.  

OSGi Component Properties
In order to illustrate this, I would like to consider Sling ResourceChangeListener which expects the PATHS (mandatory property) to which it should listen to and optional CHANGES (added/removed/changed) and PROPERTY_NAMES_HINT (property name on the resource)

For static property values, we would write an Implementation for Listener like below. Sling ResourceChangeListener

Now for amending properties dynamically via Config Admin, we can create OCD in a separate file or within the same OSGi component.
In this case, ResourceChangeListener.PATHS is a field for the constant value - resource.paths. Hence @AttributeDefinition would be resource_paths(). Same way for other two properties.

Complete code snippet : 


On a long run, if we are to move to AEM as a Cloud service, this use case of dynamically amending properties via Config Admin/run time changes will not be applicable. However, if there is a situation of run mode specific OSGi component properties needs, then we can create OSGi config like we usually do for custom properties. (code level changes/ no run time)

Using the same example, 
  • Generic config listens for change of jcr:lastModified property on specified Asset resource. 
  • Author listens for change of cq:lastModified property on specified Page resource

OSGi Config - ResourceChangeListener


OSGi Config - ResourceChangeListener


I had a chance to respond to similar query in the Community, sharing the respective thread for reference -  https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/multiple-paths-handling-in-eventhandler-not-working/m-p/426921

Comments

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  3. varshakushNovember 28, 2024 at 3:29 AM

    "This is a very insightful post! Understanding how to use OCD dynamically with OSGi components makes customization much easier."
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  4. abhayNovember 28, 2024 at 3:34 AM

    "Thanks for explaining the process with such clarity. Sling ResourceChangeListener integration is a great example!"
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  5. amanNovember 28, 2024 at 3:36 AM

    "I was looking for a practical use case of dynamically setting OSGi properties—this article is perfect!"
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  6. Techno worldsNovember 28, 2024 at 3:38 AM

    "Great article! Can you also elaborate on how this approach compares to using static configurations?"
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  7. ShinetowineNovember 28, 2024 at 3:40 AM

    "Dynamic property setting in OSGi opens up so many possibilities. Thanks for sharing this example!"
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  8. gautamNovember 28, 2024 at 3:41 AM

    "The step-by-step breakdown is very helpful. It simplifies an otherwise complex topic."
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  9. getindustrialproductsNovember 28, 2024 at 3:42 AM

    "Would love to see more real-world examples of where this method can be applied."
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  10. karishmaNovember 28, 2024 at 3:45 AM

    "This post clarified a lot of confusion I had about OSGi Component configurations. Thanks!"
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  11. muskanNovember 28, 2024 at 3:47 AM

    "Amazing write-up! Can this method also be applied to non-Sling-related OSGi components?"
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  12. NainaNovember 28, 2024 at 3:48 AM

    "Dynamic OCD settings are a game-changer for developers. Thanks for highlighting this use case."
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  13. Nishi8171November 28, 2024 at 3:49 AM

    "I appreciate the detailed explanation. Could you add a section on common pitfalls and how to avoid them?"
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    "Very well written! The example with Sling ResourceChangeListener made the concept clear."
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  15. prachiNovember 28, 2024 at 3:52 AM

    "This is exactly what I needed for my project. Thank you for such a clear and concise guide!"
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  16. RahulNovember 28, 2024 at 3:53 AM

    "Fantastic post! How does this impact performance in large-scale applications?"
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  17. shivaniwebdesigningNovember 28, 2024 at 3:55 AM

    "I learned something new today. Thank you for making dynamic OSGi properties so accessible."
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