Merge pull request 'Add DeadEvent' (#9) from f/dead-event into develop

Reviewed-on: https://git.kske.dev/kske/event-bus/pulls/9
Reviewed-by: delvh <leon@kske.dev>
Reviewed-by: DieGurke <maxi@kske.dev>
This commit is contained in:
Kai S. K. Engelbart 2021-02-21 09:16:32 +01:00
commit 0f9b64be48
Signed by: Käfer & Engelbart Git
GPG Key ID: 70F2F9206EDC1FCE
5 changed files with 115 additions and 17 deletions

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@ -0,0 +1,37 @@
package dev.kske.eventbus.core;
/**
* Wraps an event that was dispatched but for which no handler has been bound.
* <p>
* Handling dead events is useful as it can identify a poorly configured event distribution.
*
* @author Kai S. K. Engelbart
* @since 1.1.0
*/
public final class DeadEvent {
private final EventBus eventBus;
private final Object event;
DeadEvent(EventBus eventBus, Object event) {
this.eventBus = eventBus;
this.event = event;
}
@Override
public String toString() {
return String.format("DeadEvent[eventBus=%s, event=%s]", eventBus, event);
}
/**
* @return the event bus that dispatched this event
* @since 1.1.0
*/
public EventBus getEventBus() { return eventBus; }
/**
* @return the event that could not be delivered
* @since 1.1.0
*/
public Object getEvent() { return event; }
}

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@ -73,13 +73,24 @@ public final class EventBus {
var state = dispatchState.get(); var state = dispatchState.get();
state.isDispatching = true; state.isDispatching = true;
for (var handler : getHandlersFor(event.getClass())) Iterator<EventHandler> handlers = getHandlersFor(event.getClass());
if (handlers.hasNext()) {
while (handlers.hasNext())
if (state.isCancelled) { if (state.isCancelled) {
logger.log(Level.INFO, "Cancelled dispatching event {0}", event); logger.log(Level.INFO, "Cancelled dispatching event {0}", event);
state.isCancelled = false; state.isCancelled = false;
break; break;
} else { } else {
handler.execute(event); handlers.next().execute(event);
}
} else if (!(event instanceof DeadEvent)) {
// Dispatch dead event
dispatch(new DeadEvent(this, event));
} else {
// Warn about the dead event not being handled
logger.log(Level.WARNING, "{0} not handled", event);
} }
// Reset dispatch state // Reset dispatch state
@ -89,25 +100,26 @@ public final class EventBus {
} }
/** /**
* Searches for the event handlers bound to an event class. * Searches for the event handlers bound to an event class. This includes polymorphic handlers
* that are bound to a supertype of the event class.
* *
* @param eventClass the event class to use for the search * @param eventClass the event class to use for the search
* @return all event handlers registered for the event class * @return an iterator over the applicable handlers in descending order of priority
* @since 0.0.1 * @since 0.0.1
*/ */
private List<EventHandler> getHandlersFor(Class<?> eventClass) { private Iterator<EventHandler> getHandlersFor(Class<?> eventClass) {
// Get handlers defined for the event class // Get handlers defined for the event class
Set<EventHandler> handlers = bindings.getOrDefault(eventClass, new TreeSet<>()); TreeSet<EventHandler> handlers = bindings.getOrDefault(eventClass, new TreeSet<>());
// Get subtype handlers // Get polymorphic handlers
for (var binding : bindings.entrySet()) for (var binding : bindings.entrySet())
if (binding.getKey().isAssignableFrom(eventClass)) if (binding.getKey().isAssignableFrom(eventClass))
for (var handler : binding.getValue()) for (var handler : binding.getValue())
if (handler.isPolymorphic()) if (handler.isPolymorphic())
handlers.add(handler); handlers.add(handler);
return new ArrayList<>(handlers); return handlers.iterator();
} }
/** /**

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@ -68,7 +68,7 @@ final class EventHandler implements Comparable<EventHandler> {
* Compares this to another event handler based on priority. In case of equal priority a * Compares this to another event handler based on priority. In case of equal priority a
* non-zero value based on hash codes is returned. * non-zero value based on hash codes is returned.
* <p> * <p>
* This is used to retrieve event handlers in order of descending priority from a tree set. * This is used to retrieve event handlers in descending order of priority from a tree set.
* *
* @since 0.0.1 * @since 0.0.1
*/ */

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@ -0,0 +1,49 @@
package dev.kske.eventbus.core;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.Test;
/**
* Tests the dispatching of a dead event if an event could not be delivered.
*
* @author Kai S. K. Engelbart
* @since 1.1.0
*/
class DeadTest {
EventBus bus = new EventBus();
String event = "This event has no handler";
boolean deadEventHandled;
/**
* Tests dead event delivery.
*
* @since 1.1.0
*/
@Test
void testDeadEvent() {
bus.registerListener(this);
bus.dispatch(event);
assertTrue(deadEventHandled);
bus.removeListener(this);
}
/**
* Tests how the event bus reacts to an unhandled dead event. This should not lead to an
* exception or endless recursion and instead be logged.
*
* @since 1.1.0
*/
@Test
void testUnhandledDeadEvent() {
bus.dispatch(event);
}
@Event
void onDeadEvent(DeadEvent deadEvent) {
assertEquals(bus, deadEvent.getEventBus());
assertEquals(event, deadEvent.getEvent());
deadEventHandled = true;
}
}

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@ -27,8 +27,8 @@ class DispatchTest {
} }
/** /**
* Tests {@link EventBus#dispatch(Object)} with multiple handler priorities, a subtype handler * Tests {@link EventBus#dispatch(Object)} with multiple handler priorities, a polymorphic
* and a static handler. * handler and a static handler.
* *
* @since 0.0.1 * @since 0.0.1
*/ */