How to share a configuration across multiple OSGI services in AEM

Question

In AEM, I need to configure a list of strings and share it across multiple services. What is the best way to accomplish this? The list needs to be configurable at run time.

Answer 1

You could create a dedicated configuration service that you configure and that is referenced by all other OSGi services that require one or more of the configured values.

Example configuration service

import org.apache.felix.scr.annotations.Activate;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Property;
import org.apache.felix.scr.annotations.Service;
import org.apache.sling.commons.osgi.PropertiesUtil;
import org.osgi.service.component.ComponentContext;

@Service(ConfigurationService.class)
@Component(immediate = true, metatype = true)
public class ConfigurationService {

    @Property
    private static final String CONF_VALUE1 = "configuration.value1";
    private String value1;

    @Property
    private static final String CONF_VALUE2 = "configuration.value2";
    private String value2;

    @Activate
    public void activate(final ComponentContext componentContext) {
        this.value1 = PropertiesUtil.toString(componentContext.get(CONF_VALUE1), "");
        this.value2 = PropertiesUtil.toString(componentContext.get(CONF_VALUE2), "");
    }

    public String getValue1() {
        return this.value1;
    }

    public String getValue2() {
        return this.value2;
    }
}

This is the bare minimum of such a class. But it will create a configurable OSGi service that you can configure in Apache Felix Configuration Manager ( /system/console/configMgr ).

Note: It is important to use metatype = true in the @Component annotation.

The next step is to reference this service in the "consuming" services.

import org.apache.felix.scr.annotations.Activate;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Reference;
import org.apache.felix.scr.annotations.Service;
import org.osgi.service.component.ComponentContext;

@Service(MyService.class)
@Component(immediate = true, metatype = true)
public class MyService {

    @Reference
    private ConfigurationService configurationService;

    @Activate
    public void activate(final ComponentContext componentContext) {
        this.configurationService.getValue1();
    }
}

Note: This example uses the Apache SCR annotations which can be used with AEM out of the box. You can learn more about SCR annotations used in this example ( @Service , @Component , @Property , @Reference ) in the official documentation: Apache Felix SCR Annotation Documentation