Servlet Filter with single dispatcher causes ClassCastException

• Type: Regression Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.1.10 DXP FP9
• Fix Version/s: 7.1.10 DXP FP10, 7.1.10.2 SP2, 7.1.3 CE GA4, 7.1.X, Master
• Component/s: Core Infrastructure
• Labels:
  • ee-ts
  • liferay-dxp-71-sp2
  • liferay-fixpack-dxp-10-7110
• Branch Version/s:
  7.1.x
• Backported to Branch:
  Committed
• Story Points: 0.25
• Fix Priority: 3
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/71053

Use case

Define only a single dispatcher for a filter.

1. Start portal
2. Deploy com.liferay.support.filter-1.0.0.jar

 Expected behaviour: Filter deploys correctly
 Actual behaviour: ClassCastException as the single dispatcher as String object but a String array is expected 

Background

LPS-88047 changed how the dispatchers are retrieved from the components. Prior to LPS-88047 StringPlus.asList() method call was made on the retrieved data before setting "dispatchers" on the FilterMapping, and it converted the single String objects to a one element Array.
https://github.com/brianchandotcom/liferay-portal/pull/66080/files#diff-ffc4c52c819af6823153be5f7c2524f0L513

After LPS-88047, we expect Array of Strings without any casting which can lead to ClassCastException when only one "dispatcher" type is defined.
https://github.com/brianchandotcom/liferay-portal/pull/66080/files#diff-ffc4c52c819af6823153be5f7c2524f0R512

2019-03-12 15:56:58.289 ERROR [Framework Event Dispatcher: Equinox Container: 476fafed-7105-42cb-a7ae-10108d2d4936][org_eclipse_osgi:97] FrameworkEvent ERROR 
java.lang.ClassCastException: java.lang.String cannot be cast to [Ljava.lang.String;
 at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterHelper$FilterServiceTrackerCustomizer.addingService(InvokerFilterHelper.java:514)
 at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterHelper$FilterServiceTrackerCustomizer.addingService(InvokerFilterHelper.java:449)
 at com.liferay.registry.internal.ServiceTrackerCustomizerAdapter.addingService(ServiceTrackerCustomizerAdapter.java:35)
 at org.osgi.util.tracker.ServiceTracker$Tracked.customizerAdding(ServiceTracker.java:943)
 at org.osgi.util.tracker.ServiceTracker$Tracked.customizerAdding(ServiceTracker.java:1)
 at org.osgi.util.tracker.AbstractTracked.trackAdding(AbstractTracked.java:256)
 at org.osgi.util.tracker.AbstractTracked.track(AbstractTracked.java:229)
 at org.osgi.util.tracker.ServiceTracker$Tracked.serviceChanged(ServiceTracker.java:903)
 at org.eclipse.osgi.internal.serviceregistry.FilteredServiceListener.serviceChanged(FilteredServiceListener.java:109)
 at org.eclipse.osgi.internal.serviceregistry.ServiceRegistry.publishServiceEventPrivileged(ServiceRegistry.java:891)
 at org.eclipse.osgi.internal.serviceregistry.ServiceRegistry.publishServiceEvent(ServiceRegistry.java:804)
 at org.eclipse.osgi.internal.serviceregistry.ServiceRegistrationImpl.register(ServiceRegistrationImpl.java:127)
 at org.eclipse.osgi.internal.serviceregistry.ServiceRegistry.registerService(ServiceRegistry.java:228)
 at org.eclipse.osgi.internal.framework.BundleContextImpl.registerService(BundleContextImpl.java:469)
 at org.apache.felix.scr.impl.manager.AbstractComponentManager$3.register(AbstractComponentManager.java:906)
 at org.apache.felix.scr.impl.manager.AbstractComponentManager$3.register(AbstractComponentManager.java:892)
 at org.apache.felix.scr.impl.manager.RegistrationManager.changeRegistration(RegistrationManager.java:128)
 at org.apache.felix.scr.impl.manager.AbstractComponentManager.registerService(AbstractComponentManager.java:959)
 at org.apache.felix.scr.impl.manager.AbstractComponentManager.activateInternal(AbstractComponentManager.java:732)
 at org.apache.felix.scr.impl.manager.AbstractComponentManager.enableInternal(AbstractComponentManager.java:666)
 at org.apache.felix.scr.impl.manager.AbstractComponentManager.enable(AbstractComponentManager.java:432)
 at org.apache.felix.scr.impl.manager.ConfigurableComponentHolder.enableComponents(ConfigurableComponentHolder.java:665)
 at org.apache.felix.scr.impl.BundleComponentActivator.initialEnable(BundleComponentActivator.java:339)
 at org.apache.felix.scr.impl.Activator.loadComponents(Activator.java:381)
 at org.apache.felix.scr.impl.Activator.access$200(Activator.java:49)
 at org.apache.felix.scr.impl.Activator$ScrExtension.start(Activator.java:263)
 at org.apache.felix.scr.impl.AbstractExtender.createExtension(AbstractExtender.java:196)
 at org.apache.felix.scr.impl.AbstractExtender.modifiedBundle(AbstractExtender.java:169)
 at org.apache.felix.scr.impl.AbstractExtender.modifiedBundle(AbstractExtender.java:49)
 at org.osgi.util.tracker.BundleTracker$Tracked.customizerModified(BundleTracker.java:488)
 at org.osgi.util.tracker.BundleTracker$Tracked.customizerModified(BundleTracker.java:1)
 at org.osgi.util.tracker.AbstractTracked.track(AbstractTracked.java:232)
 at org.osgi.util.tracker.BundleTracker$Tracked.bundleChanged(BundleTracker.java:450)
 at org.eclipse.osgi.internal.framework.BundleContextImpl.dispatchEvent(BundleContextImpl.java:908)
 at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230)
 at org.eclipse.osgi.framework.eventmgr.ListenerQueue.dispatchEventSynchronous(ListenerQueue.java:148)
 at org.eclipse.osgi.internal.framework.EquinoxEventPublisher.publishBundleEventPrivileged(EquinoxEventPublisher.java:230)
 at org.eclipse.osgi.internal.framework.EquinoxEventPublisher.publishBundleEvent(EquinoxEventPublisher.java:137)
 at org.eclipse.osgi.internal.framework.EquinoxEventPublisher.publishBundleEvent(EquinoxEventPublisher.java:129)
 at org.eclipse.osgi.internal.framework.EquinoxContainerAdaptor.publishModuleEvent(EquinoxContainerAdaptor.java:191)
 at org.eclipse.osgi.container.Module.publishEvent(Module.java:476)
 at org.eclipse.osgi.container.Module.start(Module.java:467)
 at org.eclipse.osgi.framework.util.SecureAction.start(SecureAction.java:468)
 at org.eclipse.osgi.container.ModuleContainer.start(ModuleContainer.java:777)
 at org.eclipse.osgi.container.ModuleContainer.applyDelta(ModuleContainer.java:768)
 at org.eclipse.osgi.container.ModuleContainer.resolveAndApply(ModuleContainer.java:538)
 at org.eclipse.osgi.container.ModuleContainer.resolve(ModuleContainer.java:484)
 at org.eclipse.osgi.container.ModuleContainer.refresh(ModuleContainer.java:1028)
 at org.eclipse.osgi.container.ModuleContainer$ContainerWiring.dispatchEvent(ModuleContainer.java:1409)
 at org.eclipse.osgi.container.ModuleContainer$ContainerWiring.dispatchEvent(ModuleContainer.java:1)
 at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230)
 at org.eclipse.osgi.framework.eventmgr.EventManager$EventThread.run(EventManager.java:340)
2019-03-12 15:56:58.379 INFO  [Refresh Thread: Equinox Container: 476fafed-7105-42cb-a7ae-10108d2d4936][BundleStartStopLogger:39] STARTED com.liferay.support.filter_1.0.0 [959]

I've also attached my PoC sample, the behaviour can be verified with it, if we modify the component annotation and add/remove a dispatcher like:
"dispatcher=FORWARD",