[WICKET-5541] NullPointerException in SubscribeAnnotationEventSubscriptionInvoker on remove of component from page

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 6.14.0
• Fix Version/s: 7.0.0-M1, 6.15.0
• Component/s: wicket-atmosphere
• Assignee: Emond Papegaaij
• Reporter: Christian Wellekötter
• Created: 24/Mar/14 14:00
• Updated: 01/Apr/14 19:24
• Resolved: 01/Apr/14 19:24

Description

Following NullPointerException occurs on atmosphere event subscription, if the component, belonging to this event was removed from page before:

java.lang.NullPointerException: null
at org.apache.wicket.atmosphere.SubscribeAnnotationEventSubscriptionInvoker.invoke(SubscribeAnnotationEventSubscriptionInvoker.java:34) ~[wicket-atmosphere-0.16.jar:0.16]
at org.apache.wicket.atmosphere.AtmosphereRequestHandler.invokeMethod(AtmosphereRequestHandler.java:104) ~[wicket-atmosphere-0.16.jar:0.16]
at org.apache.wicket.atmosphere.AtmosphereRequestHandler.executeHandlers(AtmosphereRequestHandler.java:81) ~[wicket-atmosphere-0.16.jar:0.16]
at org.apache.wicket.atmosphere.AtmosphereRequestHandler.respond(AtmosphereRequestHandler.java:70) ~[wicket-atmosphere-0.16.jar:0.16]
at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:862) ~[wicket-core-6.14.0.jar:6.14.0]
at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64) ~[wicket-request-6.14.0.jar:6.14.0]
at org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:261) [wicket-core-6.14.0.jar:6.14.0]
at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:218) [wicket-core-6.14.0.jar:6.14.0]
at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:289) [wicket-core-6.14.0.jar:6.14.0]
at org.apache.wicket.atmosphere.EventBus.post(EventBus.java:372) [wicket-atmosphere-0.16.jar:0.16]
at org.apache.wicket.atmosphere.EventBus.postToSingleResource(EventBus.java:348) [wicket-atmosphere-0.16.jar:0.16]
at org.apache.wicket.atmosphere.EventBus.post(EventBus.java:323) [wicket-atmosphere-0.16.jar:0.16]
...

If you have got a component on a page with a public method that has a "Subscribe" annotation, the component / the path to the component gets registered to the corresponding page. But if you remove the component from the page the subscription does not get removed. A following atmosphere event could invoke this exception.

As a workaround I added a null check in my own SubscribeAnnotationEventSubscriptionInvoker:

public void invoke(AjaxRequestTarget target, EventSubscription subscription, Object base, AtmosphereEvent event, AjaxRequestInitializer ajaxRequestInitializer) {
if (base != null)

{ ... }

}