Your achievements

Level 1

0% to

Level 2

Tip /
Sign in

Sign in to Community

to gain points, level up, and earn exciting badges like the new
Bedrock Mission!

Learn more

View all

Sign in to view all badges

ResourceChangeListener strange behaviour

Avatar

Level 1

Hello,

I have a simple scenario - a node in the repository that we want to 'observe' and perform some action in case this node changes. ResourceChangeListener (https://sling.apache.org/apidocs/sling9/org/apache/sling/api/resource/observation/ResourceChangeList...) looked very promising, however I ran into couple of problems.

 

1) Sample component declaration (simplified)

 

(
        service = ResourceChangeListener.class,
        immediate = true,
        property = {
                ResourceChangeListener.PATHS + "=/apps/globallink-adaptor/config/repositories/blueprint",
                ResourceChangeListener.PATHS + "=/apps/globallink-adaptor/config/repositories/blueprint-xf",
                ResourceChangeListener.CHANGES + "=ADDED",
                ResourceChangeListener.CHANGES + "=CHANGED",
                ResourceChangeListener.CHANGES + "=REMOVED",
        }
)
@ServiceDescription("Custom change listener")
public class CustomListener implements ResourceChangeListener {

 
    public void onChange(List<ResourceChange> changeList) {
        for (ResourceChange resourceChange : changeList){
            LOGGER.info("==> Caught change. Change type: {}, Change target: {}, UserID: {}", resourceChange.getType(), resourceChange.getPath(), resourceChange.getUserId() );
        }
}

 

 

2) And now the problems:

- whenever I change the 'observed' node(s) I can see the listeners triggers number of times (between 1 - 4, I haven't found any pattern), visible in the log

 

2022-07-08 16:38:39.577 INFO [obfuscated] ==> Caught change. Change type: CHANGED, Change target: /apps/globallink-adaptor/config/repositories/blueprint-xf, UserID: admin
2022-07-08 16:38:39.579 INFO [obfuscated] ==> Caught change. Change type: CHANGED, Change target: /apps/globallink-adaptor/config/repositories/blueprint-xf, UserID: admin
2022-07-08 16:38:39.581 INFO [obfuscated] ==> Caught change. Change type: CHANGED, Change target: /apps/globallink-adaptor/config/repositories/blueprint-xf, UserID: admin
2022-07-08 16:38:39.585 INFO [obfuscated] ==> Caught change. Change type: CHANGED, Change target: /apps/globallink-adaptor/config/repositories/blueprint-xf, UserID: admin

 

 - in my code I'm performing certain operations like getting ResourceResolver from service user, for some of these triggers (all caused by a single change) this seems to fail without any reason in the logs why that would be so

- if I make an update to my code and push changes to local AEM, changes are NOT always propagated into executed code (perhaps some caching?). I can see that for example when I modify the message being logged, AEM keeps on logging as per the original code. Additionally when I'm debugging via remote java app I sometimes get the warning in my IDE that source code does not match the executed code.

 

When I raised this to the Adobe support I got l was told they did not support customization (yes, very helpful). I was wondering if anyone here has run into similar behaviour?

Thanks!

6 Replies

Avatar

Level 8

Hi @user08928 Tried out the same on AEM 6.5.12 and for me it is working as designed.

shaileshbassi_0-1657297495955.png

The only difference is I am using the Annotations in a different way. You can try this and check

Code Snippet

import java.util.List;

import org.apache.sling.api.resource.observation.ResourceChange;
import org.apache.sling.api.resource.observation.ResourceChangeListener;
import org.osgi.service.component.annotations.Component;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Component(
		immediate = true,
	    service = ResourceChangeListener.class,
	    property = {
	        ResourceChangeListener.PATHS+"="+"/content/mysite/us/en",	        	       
	        ResourceChangeListener.CHANGES+"="+"ADDED",
	        ResourceChangeListener.CHANGES+"="+"REMOVED",
	        ResourceChangeListener.CHANGES+"="+"CHANGED"
	    }
)	     
public class CustomListener implements ResourceChangeListener {

	private final Logger logger = LoggerFactory.getLogger(CustomListener.class);

	@Override
	public void onChange(List<ResourceChange> changeList) {
		logger.info("starting");
		// TODO Auto-generated method stub
		for (ResourceChange resourceChange : changeList){
			logger.info("==> Caught change. Change type: {}, Change target: {}, UserID: {}", resourceChange.getType(), resourceChange.getPath(), resourceChange.getUserId() );
        }
		logger.info("end");
	}
}

 

Avatar

Level 1

The only difference I can see is that you're constructing the key:value pair slightly differently. I have tried both ways and no difference - if I check the service in the OSGi console, the config looks the same (so apparently it probably makes no difference how is the annotation constructed).

 

Also, the OSGi headers look the same (which is what AEM uses to use as service description in the OSGi console).

 

<scr:component xmlns:scr="http://www.osgi.org/xmlns/scr/v1.3.0" name="dhl.logistics.tools.tdcblueprintcopy.listeners.TDCConfigUpdateListener" immediate="true">
  <property name="service.description" type="String" value="TDC blueprint change listener"/>
  <property name="resource.change.types" type="String">ADDED
REMOVED
CHANGED</property>
  <property name="resource.paths" type="String">/apps/globallink-adaptor/config/repositories/blueprint
/apps/globallink-adaptor/config/repositories/blueprint-xf</property>

Avatar

Level 4

Hi @user08928 

There are two major problems in your question. 

  1.  Your Listner is calling more than once for a simple change.
  2. Your IDE code & Code installed in OSGI is different.

Let's see first problem now, Only way a listener is called more than once is its getting multiple requests from same node. This happens when you have any dependencies on that node value.

 

Try to implement a workflow via Launcher & see if you have same problem there.

 

Second Problem: Your code in IDE is updated as per you, but when you do 

mvn clean install -PautoInstallPackage

the new jar file will be deployed in OSGI, however since your new jar file & old jar file has same POM versions, sometimes OSGI don't just install new jar. So it's our responsibility to check the installation time on the OSGI console for our bundles.

 

Please check for the below value every time you install a new jar.

 

 

Screen Shot 2022-07-08 at 1.18.29 PM.png

 

~Aditya.Ch

Avatar

Level 1

Thank you for your response. I'm dealing with snapshot versions only (where AEM behaviour is different than with 'release' versions) and this is a behaviour I have not yet observed before (where jar file wouldn't have been updated correctly). It seems to only happen with this particular functionality (it's not the only thing going on in the bundle of course).

 

It's a good tip to check the bundle installation date though, thanks for that!

Avatar

Level 4

Hi @user08928 ,  did you find out what is happening with that bundle..? Is this thing resolved?

Please let me know what you have done about it.!

Avatar

Level 1

Sadly, no. I have spoken to Adobe consultant our project uses, but he wasn't sure either, however he did not think it was an environmental issue.