[WICKET-5466] ListenerInterfaceRequestHandler#respond throws ComponentNotFoundException as a side-effect

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 6.12.0
• Fix Version/s: 6.14.0, 7.0.0-M1
• Component/s: wicket
• Assignee: Sven Meier
• Reporter: Christoph Läubrich
• Created: 08/Jan/14 19:25
• Updated: 14/Jan/14 16:01
• Resolved: 14/Jan/14 16:01

Description

The following exception occurs instead of a generic WicketRuntimeException:

16:27:56.181 WARN (RequestCycle.java:343) Handling the following exception [qtp9826071-207]
org.apache.wicket.core.request.handler.ComponentNotFoundException: Could not find component 'xyz' on page 'class MyPage’
at org.apache.wicket.core.request.handler.PageAndComponentProvider.getComponent(PageAndComponentProvider.java:182) ~[org.apache.wicket.core_6.12.0.jar:6.12.0]
at org.apache.wicket.core.request.handler.ListenerInterfaceRequestHandler.getComponent(ListenerInterfaceRequestHandler.java:90) ~[org.apache.wicket.core_6.12.0.jar:6.12.0]
at org.apache.wicket.core.request.handler.ListenerInterfaceRequestHandler.respond(ListenerInterfaceRequestHandler.java:231) ~[org.apache.wicket.core_6.12.0.jar:6.12.0]
at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:861) ~[org.apache.wicket.core_6.12.0.jar:6.12.0]
at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64) ~[org.apache.wicket.request_6.12.0.jar:6.12.0]
at org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:261) [org.apache.wicket.core_6.12.0.jar:6.12.0]
at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:218) [org.apache.wicket.core_6.12.0.jar:6.12.0]
at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:289) [org.apache.wicket.core_6.12.0.jar:6.12.0]
at org.apache.wicket.protocol.http.WicketFilter.processRequestCycle(WicketFilter.java:259) [org.apache.wicket.core_6.12.0.jar:6.12.0]

in fact, this is a side effect, if you look at the code:

@Override
public void respond(final IRequestCycle requestCycle)
{
final IRequestablePage page = getPage();
final boolean freshPage = pageComponentProvider.isPageInstanceFresh();
final boolean isAjax = ((WebRequest)requestCycle.getRequest()).isAjax();
IRequestableComponent component = null;
try

{ component = getComponent(); }

catch (ComponentNotFoundException e)

{ // either the page is stateless and the component we are looking for is not added in the // constructor // or the page is stateful+stale and a new instances was created by pageprovider // we denote this by setting component to null component = null; }

if ((component == null && freshPage) ||

(component != null && getComponent().getPage() == page))

{ [....] }

else

{ throw new WicketRuntimeException("Component " + getComponent() + " has been removed from page."); }

}

You see that getComponent() is called twice.

1) Once guarded by a catch

• and -
  2) once unguarded

So if the component can't be found AND freshPage is false, as a sideeffect instead of the WicketRuntimeException with the removed message a componentnotfound exception is raised as a side effect.

I see two possible solutions for this

a) either it is intentional that a ComponentNotFoundException is thrown, then it should be thrown from the catch block like

catch (ComponentNotFoundException e)
{
if (!freshPage)

{ throw e; }

}

b) if it is unintentionall in the else case ther should be a simple check like this

if (component == null)

{ throw new WicketRuntimeException("Component for path " + getPath() + " and page "+page.getClass().getName()+" has been removed from page."); }

else

{ throw new WicketRuntimeException("Component " + component + " has been removed from page."); }

Beside this: it would be a good idea to mention at least the page class in either case.