ResourceChangeListener

Question

I'm writing a ResourceChangeListener to check for changes in a particular property ( for ex : "cq:lastReplicated") But the listener gets triggered for any kind of change, I want it to listen only to the property specified in the "ResourceChangeListener.PROPERTY_NAMES_HINT" I don't want to use EventListener because I need to listen to multiple changes at onceHere is my example code package com.demo.core.jobs;

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;
import org.osgi.framework.Constants;

/**
 * ResourceChangeListener
 */
@Component(service = ResourceChangeListener.class, property = {
        Constants.SERVICE_DESCRIPTION + "=Demo to listen on changes in the replication",
        ResourceChangeListener.PATHS + "=" + "/content/dam",
        ResourceChangeListener.CHANGES + "=" + "CHANGED",
        ResourceChangeListener.PROPERTY_NAMES_HINT + "=" + "cq:lastReplicated"
})
public class ResourceListenerTest implements ResourceChangeListener {

/**
     * logger for logging.
     */
    private final Logger logger = LoggerFactory.getLogger(getClass());

/**
     * Override
     */
    
    public final void onChange(final List<ResourceChange> changes) {

for (ResourceChange change : changes) {
            String path = change.getPath();
            logger.info("Handling resource change at: {}", path);
        }

}

}   Any suggestion on how to make this work would be appreciated. Thanks

aanchal-sikka · Accepted Answer

Hi @aanchal-sikka

I want to know the name of the property that has been changed, path isn't of much use in my case

@hiteshra3

If my memory serves me right, following combination of path regex and getPath returns path till property.

@Component(service = ResourceChangeListener.class,
        immediate = true,
        property = {
                ResourceChangeListener.PATHS + "=glob:/content/techrevelaemsite/us/**/products/**",
                ResourceChangeListener.CHANGES + "=" + "ADDED",
                ResourceChangeListener.CHANGES + "=" + "CHANGED",
                ResourceChangeListener.CHANGES + "=" + "REMOVED"
        }
)
public class SimpleResourceListener implements ResourceChangeListener {
    private final Logger logger = LoggerFactory.getLogger(getClass());

    @Override
    public void onChange(List<ResourceChange> changes) 
        changes.forEach(change -> {
            logger.info("Resource event: {} at: {}", change.getType(), change.getPath());
        });
    }
}

Source: https://techrevel.blog/2017/03/15/resourcechangelistener/

Jineet_Vora · Answer

@hiteshra3 - From the Apache documentation mentioned here https://sling.apache.org/apidocs/sling9/org/apache/sling/api/resource/observation/ResourceChangeListener.html#PROPERTY_NAMES_HINT, its states below:

An optional hint indicating to the underlying implementation that for changes regarding properties (added/removed/changed) the listener is only interested in those property names listed inhere. If the underlying implementation supports this, events for property names that are not enlisted here will not be delivered, however events concerning resources are not affected by this hint. This is only a hint, a change listener registering with this property must be prepared that the underlying implementation is not able to filter based on this property. In this case the listener gets all events as defined with the other properties.

Hope this helps!

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