Waiting on Lifecycle Events

Liferay registers lifecycle events like portal and database initialization into the OSGi service registry. Your OSGi Component or non-component class can listen for these events by way of their service registrations. The ModuleServiceLifecycle interface defines these names for the lifecycle event services:

• DATABASE_INITIALIZED
• PORTAL_INITIALIZED
• SPRING_INITIALIZED

Here you’ll learn how to wait on lifecycle event services to act on them from within a component or non-component class.

Taking action from a component

Declarative Services (DS) facilitates waiting for OSGi services and acting on them once they’re available.

Here’s a component whose doSomething method is invoked once the ModuleServiceLifecycle.PORTAL_INITIALIZED lifecycle event service and other services are available.

@Component
public class MyXyz implements XyzApi {

    // Plain old OSGi service
    @Reference
    private SomeOsgiService _someOsgiService;

    // Service Builder generated service
    @Reference
    private DDMStructureLocalService _ddmStructureLocalService;

    // Liferay lifecycle service
    @Reference(target = ModuleServiceLifecycle.PORTAL_INITIALIZED)
    private ModuleServiceLifecycle _portalInitialized;

    @Activate
    public void doSomething() {
        // `@Activate` method is only executed once all of
        // `_someOsgiService`,
        // `_ddmStructureLocalService` and
        // `_portalInitialized`
        // are set.
    }
}

Here’s how to act on services in your component:

1. For each lifecycle event service and OSGi service your component uses, add a field of that service type and add an @Reference annotation to that field. The OSGi framework binds the services to your fields. This field, for example, binds to a standard OSGi service.

   @Reference
   SomeOsgiService _someOsgiService;
   

2. To bind to a particular lifecycle event service, target its name as the ModuleServiceLifecycle interface defines. This field, for example, targets database initialization.

   @Reference(target = ModuleServiceLifecycle.DATABASE_INITIALIZED)
   ModuleServiceLifecycle _dataInitialized;
   

3. Create a method that’s triggered on the event(s) and add the @Activate annotation to that method. It’s invoked when all the service objects are bound to the component’s fields.

Your component fires (via its @Activate method) after all its service dependencies resolve. DS components are the easiest way to act on lifecycle event services.

Taking action from a non-component class

Classes that aren’t DS components can use a org.osgi.util.tracker.ServiceTracker or org.osgi.util.tracker.ServiceTrackerCustomizer as a service callback handler for the lifecycle event. If you depend on multiple services, add logic to your ServiceTracker or ServiceTrackerCustomizer to coordinate taking action when all the services are available.

To target a lifecycle event service, create a service tracker that filters on that service. Use org.osgi.framework.FrameworkUtil to create an org.osgi.framework.Filter that specifies the service. Then pass that filter as a parameter to the service tracker constructor. For example, this service tracker filters on the lifecycle service ModuleServiceLifecycle.PORTAL_INITIALIZED.

import org.osgi.framework.Filter;
import org.osgi.framework.FrameworkUtil;

Filter filter = FrameworkUtil.createFilter(
    String.format(
        "(&(objectClass=%s)%s)",
        ModuleServiceLifecycle.class.getName(),
        ModuleServiceLifecycle.PORTAL_INITIALIZED));

new ServiceTracker<>(bundleContext, filter, null);

Acting on lifecycle event services in this way requires service callback handling and some boilerplate code. Using DS components is easier and more elegant, but at least service trackers provide a way to work with lifecycle events outside of DS components.

Related Topics

Service Trackers