Add DeadEvent

A dead events wraps an event that was dispatched but not delivered to
any handler. The dead event is than dispatched to dedicated handlers.
pull/9/head
Kai S. K. Engelbart 2021-02-19 16:04:49 +01:00
parent 4a5b94a9b7
commit 0036dc4829
Signed by: kske
GPG Key ID: 8BEB13EC5DF7EF13
4 changed files with 90 additions and 15 deletions

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@ -0,0 +1,32 @@
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;
}
/**
* @return the event bus that originated 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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@ -73,14 +73,19 @@ public final class EventBus {
var state = dispatchState.get();
state.isDispatching = true;
for (var handler : getHandlersFor(event.getClass()))
if (state.isCancelled) {
logger.log(Level.INFO, "Cancelled dispatching event {0}", event);
state.isCancelled = false;
break;
} else {
handler.execute(event);
}
Iterator<EventHandler> handlers = getHandlersFor(event.getClass());
if (handlers.hasNext()) {
while (handlers.hasNext())
if (state.isCancelled) {
logger.log(Level.INFO, "Cancelled dispatching event {0}", event);
state.isCancelled = false;
break;
} else {
handlers.next().execute(event);
}
} else if (!(event instanceof DeadEvent)) {
dispatch(new DeadEvent(this, event));
}
// Reset dispatch state
state.isDispatching = false;
@ -89,25 +94,26 @@ 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
* @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
*/
private List<EventHandler> getHandlersFor(Class<?> eventClass) {
private Iterator<EventHandler> getHandlersFor(Class<?> eventClass) {
// 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())
if (binding.getKey().isAssignableFrom(eventClass))
for (var handler : binding.getValue())
if (handler.isPolymorphic())
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
* non-zero value based on hash codes is returned.
* <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
*/

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@ -0,0 +1,37 @@
package dev.kske.eventbus.core;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.*;
/**
* 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;
String event = "This event has no handler";
boolean deadEventHandled;
@BeforeEach
void registerListener() {
bus = new EventBus();
bus.registerListener(this);
}
@Test
void testDeadEvent() {
bus.dispatch(event);
assertTrue(deadEventHandled);
}
@Event
void onDeadEvent(DeadEvent deadEvent) {
assertEquals(bus, deadEvent.getEventBus());
assertEquals(event, deadEvent.getEvent());
deadEventHandled = true;
}
}