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.gitignore vendored
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/target/
/.settings/
# Maven build directories
target/
# Dependency reduced POM from Maven Shade Plugin
dependency-reduced-pom.xml
# Eclipse settings directories
.settings/

6
.project
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<projects>
</projects>
<buildSpec>
<buildCommand>
<name>org.eclipse.jdt.core.javabuilder</name>
<arguments>
</arguments>
</buildCommand>
<buildCommand>
<name>org.eclipse.m2e.core.maven2Builder</name>
<arguments>
@ -17,7 +12,6 @@
</buildCommand>
</buildSpec>
<natures>
<nature>org.eclipse.jdt.core.javanature</nature>
<nature>org.eclipse.m2e.core.maven2Nature</nature>
</natures>
</projectDescription>

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CODE_OF_CONDUCT.md Normal file
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# Contributor Code of Conduct
This project adheres to No Code of Conduct. We are all adults. We accept anyone's contributions. Nothing else matters.
For more information please visit the [No Code of Conduct](https://nocodeofconduct.com) homepage.

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pipeline {
agent any
options {
ansiColor('xterm')
}
stages {
stage('Build') {
steps {
sh 'mvn -DskipTests clean package'
}
}
stage('Test') {
steps {
sh 'mvn test'
}
post {
always {
junit '*/target/surefire-reports/*.xml'
publishCoverage adapters: [jacocoAdapter(mergeToOneReport: true, path: '*/target/site/jacoco/jacoco.xml')]
}
}
}
stage('SonarQube Analysis') {
when {
branch 'develop'
}
steps {
withSonarQubeEnv('KSKE SonarQube') {
sh 'mvn sonar:sonar'
}
}
}
}
post {
success {
archiveArtifacts artifacts: '*/target/event-bus-*.jar'
}
}
}

26
LICENSE
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MIT License Copyright (c) 2020 Kai S. K. Engelbart
Copyright 2021 Kai S. K. Engelbart
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is furnished
to do so, subject to the following conditions:
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
The above copyright notice and this permission notice (including the next
paragraph) shall be included in all copies or substantial portions of the
Software.
https://www.apache.org/licenses/LICENSE-2.0
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF
OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

257
README.md
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# Event Bus
This library allows passing events between different objects without them having a direct reference to each other.
Any class can be made an event by implementing the `IEvent` interface.
## Introduction
Using an instance of the `EventBus` class, an instant of the event class can be dispatched.
This library allows passing events between different objects without them having a direct reference to each other.
Any object can serve as an event.
Using an instance of the `EventBus` class, an instance of the event class can be dispatched.
This means that it will be forwarded to all listeners registered for it at the event bus.
To listen to events, register event handling methods using the `Event` annotation.
For this to work, the method must have a return type of `void` and declare a single parameter of the desired event type.
Additionally, the class containing the method must implement the `EventListener` interface.
In addition, a singleton instance of the event bus is provided by the `EventBus#getInstance()` method.
Lets look at a simple example: we declare the empty class `SimpleEvent` that implements `IEvent` and can thus be used as an event.
To listen to events, register event handling methods using the `Event` annotation.
For this to work, the method must declare a single parameter of the desired event type.
Alternatively, a parameter-less event handler can be declared as shown [below](#parameter-less-event-handlers).
## A Simple Example
Lets look at a simple example: we declare the empty class `SimpleEvent` whose objects can be used as events.
```java
import dev.kske.eventbus.IEvent;
public class SimpleEvent implements IEvent {}
public class SimpleEvent {}
```
Next, an event listener for the `SimpleEvent` is declared:
```java
import dev.kske.eventbus.*;
import dev.kske.eventbus.core.*;
public class SimpleEventListener implements EventListener {
public class SimpleEventListener {
public SimpleEventListener() {
EventBus eventBus = new EventBus();
// Register this listener at the event bus
eventBus.register(this);
EventBus.getInstance().register(this);
// Dispatch a SimpleEvent
eventBus.dispatch(new SimpleEvent());
EventBus.getInstance().dispatch(new SimpleEvent());
}
@Event
@ -42,4 +45,226 @@ public class SimpleEventListener implements EventListener {
}
```
In this case, an event bus is created and used locally. In a more sophisticated example the class would acquire an external event bus that is used by multiple classes.
Note that creating static event handlers like this
```java
@Event
private static void onSimpleEvent(SimpleEvent event) { ... }
```
is technically possible, however you would still have to create an instance of the event listener to register it at an event bus.
## Installation
Event Bus is available in Maven Central.
To include it inside your project, just add the following dependency to your `pom.xml`:
```xml
<dependencies>
<dependency>
<groupId>dev.kske</groupId>
<artifactId>event-bus-core</artifactId>
<version>1.2.0</version>
</dependency>
</dependencies>
```
Then, require the Event Bus Core module in your `module-info.java`:
```java
requires dev.kske.eventbus.core;
```
If you intend to use event handlers that are inaccessible to Event Bus by means of Java language access control, make sure to allow reflective access to your package for Event Bus:
```java
opens my.package to dev.kske.eventbus.core;
```
## Polymorphic Event Handlers
On certain occasions it's practical for an event handler to accept both events of the specified type, as well as subclasses of that event.
To include subtypes for an event handler, use the `@Polymorphic` annotation in addition to `@Event`:
```java
@Event
@Polymorphic
private void onSimpleEvent(SimpleEvent event) { ... }
```
## Event Handler Execution Order
Sometimes when using multiple handlers for one event, it might be useful to define in which order they will be executed.
Event Bus assigns a priority to every handler, which is `100` by default, but can be explicitly set using the `@Priority` annotation in addition to `@Event`:
```java
@Event
@Priority(250)
private void onSimpleEvent(SimpleEvent event) { ... }
```
**Important:**
Events are dispatched to handlers in descending order of their priority.
The execution order is undefined for handlers with the same priority.
## Parameter-Less Event Handlers
In some cases an event handler is not interested in the dispatched event instance.
To avoid declaring a useless parameter just to specify the event type of the handler, there is an alternative:
```java
@Event(SimpleEvent.class)
private void onSimpleEvent() {
System.out.println("SimpleEvent received!");
}
```
Make sure that you **do not** both declare a parameter and specify the event type in the annotation, as this would be ambiguous.
## Callback listeners
While defining event handlers as annotated methods is rather simple and readable, sometimes a more flexible approach is required.
For this reason, there are callback event handlers that allow the registration of an "inline" event listener consisting of just one handler in the form of a consumer:
```java
EventBus.getInstance().registerListener(SimpleEvent.class, e -> System.out.println("Received " + e));
```
The event type has to be defined explicitly, with the priority and polymorphism parameters being optional.
If you intend to remove the listener later, remember to keep a reference to it, as you would have to clear the entire event bus if you didn't.
## Listener-Level Properties
When defining a dedicated event listener that, for example, performs pre- or post-processing, all event handlers will probably have the same non-standard priority.
Instead of defining that priority for each handler, it can be defined at the listener level by annotating the listener itself.
The same applies to polymorphism.
## Event Consumption
In some cases it might be useful to stop the propagation of an event.
Event Bus makes this possible with event consumption:
```java
@Event(SimpleEvent.class)
@Priority(100)
private void onSimpleEvent() {
EventBus.getInstance().cancel();
}
@Event(SimpleEvent.class)
@Priority(50)
private void onSimpleEvent2() {
System.out.println("Will not be printed!");
}
```
In this example, the second method will not be executed as it has a lower priority and the event will not be propagated after consumption.
This applies to all event handlers that would have been executed after the one consuming the event.
**Important:**
Avoid cancelling events while using multiple event handlers with the same priority.
As event handlers are ordered by priority, it is not defined which of them will be executed after the event has been consumed.
## System Events
To accommodate for special circumstances in an event distribution, system events have been introduced.
At the moment, there are two system events, which are explained in this section.
### Detecting Unhandled Events
When an event is dispatched but not delivered to any handler, a dead event is dispatched that wraps the original event.
You can declare a dead event handler to respond to this situation:
```java
private void onDeadEvent(DeadEvent deadEvent) { ... }
```
### Detecting Exceptions Thrown by Event Handlers
When an event handler throws an exception, an exception event is dispatched that wraps the original event.
An exception handler is declared as follows:
```java
private void onExceptionEvent(ExceptionEvent ExceptionEvent) { ... }
```
Both system events reference the event bus that caused them and a warning is logged if they are unhandled.
#### Yeeting Exceptions Out of an Event Handler
In some cases, a warning about an `Exception` that was thrown in an event handler is not enough, stays unnoticed, or an exception should be catched explicitly.
Event Bus explicitly dispatches no `ExceptionEvent` when an `ExceptionWrapper` exception is thrown and instead simply rethrows it.
`ExceptionWrapper` is an unchecked exception that (as the name says) simply wraps an exception that caused it.
This means the following is possible and results in a normal program exit:
```java
@Event(String.class)
void onString() {
throw new ExceptionWrapper(new RuntimeException("I failed!"));
}
void helloStackTrace() {
EventBus.getInstance().registerListener(this);
try {
EventBus.getInstance().dispatch("A string!");
System.exit(-1);
} catch(ExceptionWrapper e) {
e.getCause().printStackTrace();
System.exit(0);
}
}
```
### What About Endless Recursion Caused By Dead Events and Exception Events?
As one might imagine, an unhandled dead event would theoretically lead to an endless recursion.
The same applies when an exception event handler throws an exception.
To avoid this, system events never cause system events and instead just issue a warning to the logger.
## Inheritance
When a superclass or an interface of an event listener defines event handlers, they will be detected and registered by Event Bus, even if they are `private`.
If an event handler is overridden by the listener, the `@Event` annotation of the overridden method is automatically considered present on the overriding method.
If the overridden method already contains an implementation in the superclass, the superclass implementation is ignored as expected.
The `@Priority` and `@Polymorphic` annotations are inherited both on a class and on a method level.
If the priority or polymorphism has to be redefined on an inherited handler, the `@Event` annotation has to be added explicitly.
## Debugging
In more complex setups, taking a look at the event handler execution order can be helpful for debugging.
Event Bus offers a method for this purpose which can be used as follows:
```java
System.out.println(EventBus.getInstance().debugExecutionOrder(SimpleEvent.class));
```
Then, the execution order can be inspected in the console.
## Compile-Time Error Checking with Event Bus Proc
To assist you with writing event listeners, the Event Bus Proc (Annotation Processor) module enforces correct usage of the `@Event` annotation during compile time.
This reduces difficult-to-debug bugs that occur during runtime to compile-time errors which can be easily fixed.
The event annotation processor detects invalid event handlers and event type issues with more to come in future versions.
When using Maven, it can be registered using the Maven Compiler Plugin:
```xml
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<annotationProcessorPaths>
<annotationProcessorPath>
<groupId>dev.kske</groupId>
<artifactId>event-bus-proc</artifactId>
<version>1.2.0</version>
</annotationProcessorPath>
</annotationProcessorPaths>
</configuration>
</plugin>
```
Alternatively, a JAR file containing the processor is offered with each release for the use within IDEs and environments without Maven support.

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.classpath → core/.classpath
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<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
<name>event-bus-core</name>
<comment></comment>
<projects>
</projects>
<buildSpec>
<buildCommand>
<name>org.eclipse.jdt.core.javabuilder</name>
<arguments>
</arguments>
</buildCommand>
<buildCommand>
<name>org.eclipse.m2e.core.maven2Builder</name>
<arguments>
</arguments>
</buildCommand>
</buildSpec>
<natures>
<nature>org.eclipse.jdt.core.javanature</nature>
<nature>org.eclipse.m2e.core.maven2Nature</nature>
</natures>
</projectDescription>

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core/pom.xml Normal file
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<artifactId>event-bus-core</artifactId>
<name>Event Bus Core</name>
<parent>
<groupId>dev.kske</groupId>
<artifactId>event-bus</artifactId>
<version>1.2.0</version>
</parent>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<version>5.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<!-- Disable resource folder -->
<resources />
<plugins>
<!-- Run unit tests -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>3.0.0-M5</version>
<configuration>
<argLine>
${argLine}
--add-opens dev.kske.eventbus.core/dev.kske.eventbus.core=ALL-UNNAMED
--add-opens dev.kske.eventbus.core/dev.kske.eventbus.core.handler=ALL-UNNAMED
</argLine>
</configuration>
</plugin>
<!-- Generate coverage report -->
<plugin>
<groupId>org.jacoco</groupId>
<artifactId>jacoco-maven-plugin</artifactId>
<version>0.8.7</version>
<executions>
<execution>
<goals>
<goal>prepare-agent</goal>
</goals>
</execution>
<execution>
<id>report</id>
<phase>test</phase>
<goals>
<goal>report</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

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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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core/src/main/java/dev/kske/eventbus/core/Event.java Normal file
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package dev.kske.eventbus.core;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.*;
/**
* Indicates that a method is an event handler.
* <p>
* To be successfully used as such, the method has to specify the event type by either declaring one
* parameter of that type or setting the annotation value to the corresponding class.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
* @see Polymorphic
* @see Priority
*/
@Documented
@Retention(RUNTIME)
@Target(METHOD)
public @interface Event {
/**
* Defines the event type the handler listens for. If this value is set, the handler is not
* allowed to declare parameters.
* <p>
* This is useful when the event handler does not utilize the event instance.
*
* @return the event type accepted by the handler
* @since 1.0.0
*/
Class<?> value() default void.class;
}

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core/src/main/java/dev/kske/eventbus/core/EventBus.java Normal file
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package dev.kske.eventbus.core;
import java.lang.System.Logger;
import java.lang.System.Logger.Level;
import java.lang.annotation.Annotation;
import java.lang.reflect.*;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Consumer;
import dev.kske.eventbus.core.handler.*;
/**
* Event listeners can be registered at an event bus to be notified when an event is dispatched.
* <p>
* A singleton instance of this class can be lazily created and acquired using the
* {@link EventBus#getInstance()} method.
*
* @implNote This is a thread-safe implementation.
* @author Kai S. K. Engelbart
* @since 0.0.1
* @see Event
*/
public final class EventBus {
/**
* Holds the state of the dispatching process on one thread.
*
* @since 0.1.0
*/
private static final class DispatchState {
/**
* Indicates that the last event handler invoked has called {@link EventBus#cancel}. In that
* case, the event is not dispatched further.
*
* @since 0.1.0
*/
boolean isCancelled;
/**
* Is incremented when {@link EventBus#dispatch(Object)} is invoked and decremented when it
* finishes. This allows keeping track of nested dispatches.
*
* @since 1.2.0
*/
int nestingCount;
}
/**
* The priority assigned to every event handler without an explicitly defined priority.
*
* @since 1.1.0
* @see Priority
*/
public static final int DEFAULT_PRIORITY = 100;
private static final EventBus singletonInstance = new EventBus();
private static final Logger logger = System.getLogger(EventBus.class.getName());
/**
* Compares event handlers based on priority, but uses hash codes for equal priorities.
*
* @implNote As the priority comparator by itself is not consistent with equals (two handlers
* with the same priority are not necessarily equal, but would have a comparison
* result of 0), the hash code is used for the fallback comparison. This way,
* consistency with equals is restored.
* @since 1.2.0
*/
private static final Comparator<EventHandler> byPriority =
Comparator.comparingInt(EventHandler::getPriority).reversed()
.thenComparingInt(EventHandler::hashCode);
/**
* Returns the default event bus, which is a statically initialized singleton instance.
*
* @return the default event bus
* @since 0.0.2
*/
public static EventBus getInstance() {
return singletonInstance;
}
/**
* Event handler bindings (target class to handlers registered for that class), does not contain
* other (polymorphic) handlers.
*
* @since 0.0.1
*/
private final Map<Class<?>, TreeSet<EventHandler>> bindings = new ConcurrentHashMap<>();
/**
* A cache mapping an event class to all handlers the event should be dispatched to. This
* includes polymorphic handlers that don't reference the event class explicitly. If an event
* class is not contained inside this cache, the {@link #bindings} have to be traversed manually
* in search of applicable handlers.
*
* @since 1.3.0
*/
private final Map<Class<?>, TreeSet<EventHandler>> bindingCache = new ConcurrentHashMap<>();
/**
* Stores all registered event listeners (which declare event handlers) and prevents them from
* being garbage collected.
*
* @since 0.0.1
*/
private final Set<Object> registeredListeners = ConcurrentHashMap.newKeySet();
/**
* The current event dispatching state, local to each thread.
*
* @since 0.1.0
*/
private final ThreadLocal<DispatchState> dispatchState =
ThreadLocal.withInitial(DispatchState::new);
/**
* Dispatches an event to all event handlers registered for it in descending order of their
* priority.
*
* @param event the event to dispatch
* @throws EventBusException if an event handler isn't accessible or has an invalid signature
* @throws ExceptionWrapper if it is thrown by an event handler
* @throws NullPointerException if the specified event is {@code null}
* @since 0.0.1
*/
public void dispatch(Object event) {
Objects.requireNonNull(event);
logger.log(Level.INFO, "Dispatching event {0}", event);
// Look up dispatch state
var state = dispatchState.get();
// Increment nesting count (becomes > 1 during nested dispatches)
++state.nestingCount;
Iterator<EventHandler> handlers = getHandlersFor(event.getClass()).iterator();
if (handlers.hasNext()) {
while (handlers.hasNext())
if (state.isCancelled) {
logger.log(Level.INFO, "Cancelled dispatching event {0}", event);
state.isCancelled = false;
break;
} else {
try {
handlers.next().execute(event);
} catch (InvocationTargetException e) {
if (e.getCause() instanceof Error)
// Transparently pass error to the caller
throw (Error) e.getCause();
else if (e.getCause() instanceof ExceptionWrapper)
// Transparently pass exception wrapper to the caller
throw (ExceptionWrapper) e.getCause();
else if (event instanceof DeadEvent || event instanceof ExceptionEvent)
// Warn about system event not being handled
logger.log(Level.WARNING, event + " not handled due to exception", e);
else
// Dispatch exception event
dispatch(new ExceptionEvent(this, event, e.getCause()));
}
}
} else if (event instanceof DeadEvent || event instanceof ExceptionEvent) {
// Warn about the dead event not being handled
logger.log(Level.WARNING, "{0} not handled", event);
} else {
// Dispatch dead event
dispatch(new DeadEvent(this, event));
}
// Decrement nesting count (becomes 0 when all dispatches on the thread are finished)
--state.nestingCount;
logger.log(Level.DEBUG, "Finished dispatching event {0}", event);
}
/**
* Searches for the event handlers bound to an event class. This includes polymorphic handlers
* that are bound to a supertype of the event class.
*
* @implNote If the given event type was requested in the past, the handlers are retrieved from
* the {@link #bindingCache}. If not, the entire {@link #bindings} are traversed in
* search of polymorphic handlers compatible with the event type.
* @param eventType the event type to use for the search
* @return a navigable set containing the applicable handlers in descending order of priority
* @since 1.2.0
*/
private NavigableSet<EventHandler> getHandlersFor(Class<?> eventType) {
return bindingCache.computeIfAbsent(eventType, k -> {
// Get handlers defined for the event class
TreeSet<EventHandler> handlers =
bindings.getOrDefault(eventType, new TreeSet<>(byPriority));
// Get polymorphic handlers
for (var binding : bindings.entrySet())
if (binding.getKey().isAssignableFrom(eventType))
for (var handler : binding.getValue())
if (handler.isPolymorphic())
handlers.add(handler);
return handlers;
});
}
/**
* Cancels an event that is currently dispatched from inside an event handler.
*
* @throws EventBusException if the calling thread is not an active dispatching thread
* @since 0.1.0
*/
public void cancel() {
var state = dispatchState.get();
if (state.nestingCount > 0 && !state.isCancelled)
state.isCancelled = true;
else
throw new EventBusException("Calling thread not an active dispatching thread!");
}
/**
* Registers an event listener at this event bus.
*
* @param listener the listener to register
* @throws EventBusException if the listener is already registered or a declared event
* handler does not comply with the specification
* @throws NullPointerException if the specified listener is {@code null}
* @since 0.0.1
* @see Event
*/
public void registerListener(Object listener) {
Objects.requireNonNull(listener);
if (registeredListeners.contains(listener))
throw new EventBusException(listener + " already registered!");
logger.log(Level.INFO, "Registering event listener {0}", listener.getClass().getName());
boolean handlerBound = false;
// Predefined handler polymorphism
boolean polymorphic = false;
if (listener.getClass().isAnnotationPresent(Polymorphic.class))
polymorphic = listener.getClass().getAnnotation(Polymorphic.class).value();
// Predefined handler priority
int priority = DEFAULT_PRIORITY;
if (listener.getClass().isAnnotationPresent(Priority.class))
priority = listener.getClass().getAnnotation(Priority.class).value();
registeredListeners.add(listener);
for (var method : getHandlerMethods(listener.getClass())) {
Event annotation = method.getAnnotation(Event.class);
// Skip methods without annotations
if (annotation == null)
continue;
// Initialize and bind the handler
bindHandler(
new ReflectiveEventHandler(listener, method, annotation, polymorphic, priority));
handlerBound = true;
}
if (!handlerBound)
logger.log(
Level.WARNING,
"No event handlers bound for event listener {0}",
listener.getClass().getName());
}
/**
* Searches for event handling methods declared inside the inheritance hierarchy of an event
* listener.
*
* @param listenerClass the class to inspect
* @return all event handling methods defined for the given listener
* @since 1.3.0
*/
private Set<Method> getHandlerMethods(Class<?> listenerClass) {
// Get methods declared by the listener
Set<Method> methods = getMethodsAnnotatedWith(listenerClass, Event.class);
// Recursively add superclass handlers
Class<?> superClass = listenerClass.getSuperclass();
if (superClass != null && superClass != Object.class)
methods.addAll(getHandlerMethods(superClass));
// Recursively add interface handlers
for (Class<?> iClass : listenerClass.getInterfaces())
methods.addAll(getHandlerMethods(iClass));
return methods;
}
/**
* Searches for declared methods with a specific annotation inside a class.
*
* @param enclosingClass the class to inspect
* @param annotationClass the annotation to look for
* @return all methods matching the search criteria
* @since 1.3.0
*/
private Set<Method> getMethodsAnnotatedWith(Class<?> enclosingClass,
Class<? extends Annotation> annotationClass) {
var methods = new HashSet<Method>();
for (var method : enclosingClass.getDeclaredMethods())
if (method.isAnnotationPresent(annotationClass))
methods.add(method);
return methods;
}
/**
* Registers a callback listener, which is a consumer that is invoked when an event occurs. The
* listener is not polymorphic and has the {@link #DEFAULT_PRIORITY}.
*
* @param <E> the event type the listener listens for
* @param eventType the event type the listener listens for
* @param eventListener the callback that is invoked when an event occurs
* @since 1.2.0
* @see #registerListener(Class, Consumer, boolean, int)
*/
public <E> void registerListener(Class<E> eventType, Consumer<E> eventListener) {
registerListener(eventType, eventListener, false, DEFAULT_PRIORITY);
}
/**
* Registers a callback listener, which is a consumer that is invoked when an event occurs. The
* listener has the {@link #DEFAULT_PRIORITY}.
*
* @param <E> the event type the listener listens for
* @param eventType the event type the listener listens for
* @param eventListener the callback that is invoked when an event occurs
* @param polymorphic whether the listener is also invoked for subtypes of the event type
* @since 1.2.0
* @see #registerListener(Class, Consumer, boolean, int)
*/
public <E> void registerListener(Class<E> eventType, Consumer<E> eventListener,
boolean polymorphic) {
registerListener(eventType, eventListener, polymorphic, DEFAULT_PRIORITY);
}
/**
* Registers a callback listener, which is a consumer that is invoked when an event occurs. The
* listener is not polymorphic.
*
* @param <E> the event type the listener listens for
* @param eventType the event type the listener listens for
* @param eventListener the callback that is invoked when an event occurs
* @param priority the priority to assign to the listener
* @since 1.2.0
* @see #registerListener(Class, Consumer, boolean, int)
*/
public <E> void registerListener(Class<E> eventType, Consumer<E> eventListener, int priority) {
registerListener(eventType, eventListener, false, priority);
}
/**
* Registers a callback listener, which is a consumer that is invoked when an event occurs.
*
* @param <E> the event type the listener listens for
* @param eventType the event type the listener listens for
* @param eventListener the callback that is invoked when an event occurs
* @param polymorphic whether the listener is also invoked for subtypes of the event type
* @param priority the priority to assign to the listener
* @since 1.2.0
*/
public <E> void registerListener(Class<E> eventType, Consumer<E> eventListener,
boolean polymorphic,
int priority) {
Objects.requireNonNull(eventListener);
if (registeredListeners.contains(eventListener))
throw new EventBusException(eventListener + " already registered!");
logger.log(Level.INFO, "Registering callback event listener {0}",
eventListener.getClass().getName());
registeredListeners.add(eventListener);
bindHandler(new CallbackEventHandler(eventType, eventListener, polymorphic, priority));
}
/**
* Inserts a new handler into the {@link #bindings} map. Additionally, the handler is placed
* inside the {@link #bindingCache} where applicable.
*
* @param handler the handler to bind
* @since 1.2.0
*/
private void bindHandler(EventHandler handler) {
// Bind handler
logger.log(Level.DEBUG, "Binding event handler {0}", handler);
bindings.computeIfAbsent(handler.getEventType(), k -> new TreeSet<>(byPriority))
.add(handler);
// Insert handler into cache
bindingCache.computeIfAbsent(handler.getEventType(), k -> new TreeSet<>(byPriority))
.add(handler);
// Handler is polymorphic => insert where applicable
if (handler.isPolymorphic())
for (var binding : bindingCache.entrySet())
if (binding.getKey().isAssignableFrom(handler.getEventType()))
binding.getValue().add(handler);
}
/**
* Removes a specific listener from this event bus.
*
* @param listener the listener to remove
* @since 0.0.1
*/
public void removeListener(Object listener) {
Objects.requireNonNull(listener);
logger.log(Level.INFO, "Removing event listener {0}", listener.getClass().getName());
// Remove bindings from binding map
for (var binding : bindings.values()) {
var it = binding.iterator();
while (it.hasNext()) {
var handler = it.next();
if (handler.getListener().equals(listener)) {
logger.log(Level.DEBUG, "Unbinding event handler {0}", handler);
it.remove();
}
}
}
// Remove bindings from cache
for (var binding : bindingCache.values()) {
var it = binding.iterator();
while (it.hasNext()) {
var handler = it.next();
if (handler.getListener().equals(listener)) {
logger.log(Level.TRACE, "Removing event handler {0} from cache", handler);
it.remove();
}
}
}
// Remove the listener itself
registeredListeners.remove(listener);
}
/**
* Removes all event listeners from this event bus.
*
* @since 0.0.1
*/
public void clearListeners() {
logger.log(Level.INFO, "Clearing event listeners");
bindings.clear();
bindingCache.clear();
registeredListeners.clear();
}
/**
* Generates a string describing the event handlers that would be executed for a specific event
* type, in order and without actually executing them.
*
* @apiNote Using this method is only recommended for debugging purposes, as the output depends
* on implementation internals which may be subject to change.
* @implNote Nested dispatches are not accounted for, as this would require actually executing
* the handlers.
* @param eventType the event type to generate the execution order for
* @return a human-readable event handler list suitable for debugging purposes
* @since 1.2.0
*/
public String debugExecutionOrder(Class<?> eventType) {
var handlers = getHandlersFor(eventType);
var sj = new StringJoiner("\n");
// Output header line
sj.add(String.format("Event handler execution order for %s (%d handler(s)):", eventType,
handlers.size()));
sj.add(
"==========================================================================================");
// Individual handlers
for (var handler : handlers)
sj.add(handler.toString());
// Bottom line
sj.add(
"==========================================================================================");
return sj.toString();
}
/**
* Provides an unmodifiable view of the event listeners registered at this event bus.
*
* @return all registered event listeners
* @since 0.0.1
*/
public Set<Object> getRegisteredListeners() {
return Collections.unmodifiableSet(registeredListeners);
}
}

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package dev.kske.eventbus.core;
/**
* This unchecked exception is specific to the event bus and can be thrown under the following
* circumstances:
* <ul>
* <li>An event handler throws an exception (which is stored as the cause)</li>
* <li>An event listener with an invalid event handler is registered</li>
* <li>{@link EventBus#cancel()} is invoked from outside an active dispatch thread</li>
* </ul>
*
* @author Kai S. K. Engelbart
* @since 0.0.1
*/
public final class EventBusException extends RuntimeException {
private static final long serialVersionUID = 7254445250300604449L;
/**
* Creates a new event bus exception.
*
* @param message the message to display
* @param cause the cause of this exception
* @since 0.0.1
*/
public EventBusException(String message, Throwable cause) {
super(message, cause);
}
/**
* Creates a new event bus exception.
*
* @param message the message to display
* @since 0.0.1
*/
public EventBusException(String message) {
super(message);
}
}

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package dev.kske.eventbus.core;
/**
* Wraps an event that was dispatched but caused an exception in one of its handlers.
* <p>
* Handling exception events is useful as it allows the creation of a centralized exception handling
* mechanism for unexpected exceptions.
*
* @author Kai S. K. Engelbart
* @since 1.1.0
*/
public final class ExceptionEvent {
private final EventBus eventBus;
private final Object event;
private final Throwable cause;
ExceptionEvent(EventBus eventBus, Object event, Throwable cause) {
this.eventBus = eventBus;
this.event = event;
this.cause = cause;
}
@Override
public String toString() {
return String.format("ExceptionEvent[eventBus=%s, event=%s, cause=%s]", eventBus, event,
cause);
}
/**
* @return the event bus that dispatched this event
* @since 1.1.0
*/
public EventBus getEventBus() { return eventBus; }
/**
* @return the event that could not be handled because of an exception
* @since 1.1.0
*/
public Object getEvent() { return event; }
/**
* @return the exception that was thrown while handling the event
* @since 1.1.0
*/
public Throwable getCause() { return cause; }
}

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package dev.kske.eventbus.core;
/**
* This unchecked exception acts as a wrapper for an arbitrary exception to prevent an
* {@link ExceptionEvent} from being dispatched. Instead, the wrapped exception is rethrown by
* {@link EventBus#dispatch(Object)}.
*
* @author Kai S. K. Engelbart
* @since 1.2.1
*/
public final class ExceptionWrapper extends RuntimeException {
private static final long serialVersionUID = -2016681140617308788L;
/**
* Creates a new exception wrapper.
*
* @param cause the exception to wrap
* @since 1.2.1
*/
public ExceptionWrapper(Exception cause) {
super(cause);
}
}

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package dev.kske.eventbus.core;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.*;
/**
* Allows an event handler to receive events that are subtypes of the declared event type.
* <p>
* When used on a type, the value applies to all event handlers declared within that type that don't
* define a value on their own.
* <p>
* This is useful when defining an event handler for an interface or an abstract class.
*
* @author Kai S. K. Engelbart
* @since 1.0.0
* @see Event
*/
@Documented
@Inherited
@Retention(RUNTIME)
@Target({ METHOD, TYPE })
public @interface Polymorphic {
/**
* @return whether the event handler is polymorphic
* @since 1.1.0
*/
boolean value() default true;
}

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package dev.kske.eventbus.core;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.*;
/**
* Defines the priority of an event handler. Handlers are executed in descending order of their
* priority.
* <p>
* When used on a type, the value applies to all event handlers declared within that type that don't
* define a value on their own.
* <p>
* Handlers without this annotation have the default priority of 100.
* <p>
* The execution order of handlers with the same priority is undefined.
*
* @author Kai S. K. Engelbart
* @since 1.0.0
* @see Event
*/
@Documented
@Inherited
@Retention(RUNTIME)
@Target({ METHOD, TYPE })
public @interface Priority {
/**
* @return the priority of the event handler
* @since 1.0.0
*/
int value();
}

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package dev.kske.eventbus.core.handler;
import java.lang.reflect.InvocationTargetException;
import java.util.function.Consumer;
/**
* An event handler wrapping a callback method.
*
* @author Kai S. K. Engelbart
* @since 1.2.0
*/
public final class CallbackEventHandler implements EventHandler {
private final Class<?> eventType;
private final Consumer<Object> callback;
private final boolean polymorphic;
private final int priority;
/**
* Constructs a callback event handler.
*
* @param <E> the event type of the handler
* @param eventType the event type of the handler
* @param callback the callback method to execute when the handler is invoked
* @param polymorphic whether the handler is polymorphic
* @param priority the priority of the handler
* @since 1.2.0
*/
@SuppressWarnings("unchecked")
public <E> CallbackEventHandler(Class<E> eventType, Consumer<E> callback, boolean polymorphic,
int priority) {
this.eventType = eventType;
this.callback = (Consumer<Object>) callback;
this.polymorphic = polymorphic;
this.priority = priority;
}
@Override
public void execute(Object event) throws InvocationTargetException {
try {
callback.accept(event);
} catch (RuntimeException e) {
throw new InvocationTargetException(e, "Callback event handler failed!");
}
}
@Override
public String toString() {
return String.format(
"CallbackEventHandler[eventType=%s, polymorphic=%b, priority=%d]",
eventType, polymorphic, priority);
}
@Override
public Consumer<?> getListener() {
return callback;
}
@Override
public Class<?> getEventType() {
return eventType;
}
@Override
public int getPriority() {
return priority;
}
@Override
public boolean isPolymorphic() {
return polymorphic;
}
}

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core/src/main/java/dev/kske/eventbus/core/handler/EventHandler.java Normal file
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package dev.kske.eventbus.core.handler;
import java.lang.reflect.InvocationTargetException;
import dev.kske.eventbus.core.*;
/**
* Internal representation of an event handling method.
*
* @author Kai S. K. Engelbart
* @since 1.2.0
* @see EventBus
*/
public interface EventHandler {
/**
* Executes the event handler.
*
* @param event the event used as the method parameter
* @throws EventBusException if the event handler isn't accessible or has an invalid
* signature
* @throws InvocationTargetException if the handler throws an exception
* @throws EventBusException if the handler has the wrong signature or is inaccessible
* @since 1.2.0
*/
void execute(Object event) throws EventBusException, InvocationTargetException;
/**
* @return the listener containing this handler
* @since 1.2.0
*/
Object getListener();
/**
* @return the event type this handler listens for
* @since 1.2.0
*/
Class<?> getEventType();
/**
* @return the priority of this handler
* @since 1.2.0
* @see Priority
*/
int getPriority();
/**
* @return whether this handler also accepts subtypes of the event type
* @since 1.2.0
* @see Polymorphic
*/
boolean isPolymorphic();
}

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package dev.kske.eventbus.core.handler;
import java.lang.reflect.*;
import dev.kske.eventbus.core.*;
/**
* An event handler wrapping a method annotated with {@link Event} and executing it using
* reflection.
*
* @author Kai S. K. Engelbart
* @since 1.2.0
*/
public final class ReflectiveEventHandler implements EventHandler {
private final Object listener;
private final Method method;
private final Class<?> eventType;
private final boolean useParameter;
private final boolean polymorphic;
private final int priority;
/**
* Constructs a reflective event handler.
*
* @param listener the listener containing the handler
* @param method the handler method
* @param annotation the event annotation
* @param defPolymorphism the predefined polymorphism (default or listener-level)
* @param defPriority the predefined priority (default or listener-level)
* @throws EventBusException if the method or the annotation do not comply with the
* specification
* @since 1.2.0
*/
public ReflectiveEventHandler(Object listener, Method method, Event annotation,
boolean defPolymorphism, int defPriority) throws EventBusException {
this.listener = listener;
this.method = method;
useParameter = annotation.value() == void.class;
// Check handler signature
if (method.getParameterCount() == 0 && useParameter)
throw new EventBusException(method + " does not define an event type!");
if (method.getParameterCount() == 1 && !useParameter)
throw new EventBusException(method + " defines an ambiguous event type!");
if (method.getParameterCount() > 1)
throw new EventBusException(method + " defines more than one parameter!");
// Determine handler properties
eventType = useParameter ? method.getParameterTypes()[0] : annotation.value();
polymorphic = method.isAnnotationPresent(Polymorphic.class)
? method.getAnnotation(Polymorphic.class).value()
: defPolymorphism;
priority = method.isAnnotationPresent(Priority.class)
? method.getAnnotation(Priority.class).value()
: defPriority;
// Try to allow access if the method is not accessible
if (!method.canAccess(Modifier.isStatic(method.getModifiers()) ? null : listener))
method.setAccessible(true);
}
@Override
public void execute(Object event) throws EventBusException, InvocationTargetException {
try {
if (useParameter)
method.invoke(getListener(), event);
else
method.invoke(getListener());
} catch (IllegalArgumentException e) {
throw new EventBusException("Event handler rejected target / argument!", e);
} catch (IllegalAccessException e) {
throw new EventBusException("Event handler is not accessible!", e);
}
}
@Override
public String toString() {
return String.format(
"ReflectiveEventHandler[eventType=%s, polymorphic=%b, priority=%d, method=%s, useParameter=%b]",
eventType, polymorphic, priority, method, useParameter);
}
@Override
public Object getListener() {
return listener;
}
@Override
public Class<?> getEventType() {
return eventType;
}
@Override
public int getPriority() {
return priority;
}
@Override
public boolean isPolymorphic() {
return polymorphic;
}
}

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/**
* Contains the internal representation of event handling methods.
*
* @author Kai S. K. Engelbart
* @since 1.2.0
* @see dev.kske.eventbus.core.handler.EventHandler
*/
package dev.kske.eventbus.core.handler;

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/**
* Contains the public API and implementation of the Event Bus library.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
* @see dev.kske.eventbus.core.Event
* @see dev.kske.eventbus.core.EventBus
*/
package dev.kske.eventbus.core;

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/**
* Contains the public API and implementation of the Event Bus library.
*
* @author Kai S. K. Engelbart
* @since 0.0.3
* @see dev.kske.eventbus.core.Event
* @see dev.kske.eventbus.core.EventBus
*/
module dev.kske.eventbus.core {
exports dev.kske.eventbus.core;
}

54
core/src/test/java/dev/kske/eventbus/core/CancelTest.java Normal file
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package dev.kske.eventbus.core;
import static org.junit.jupiter.api.Assertions.assertEquals;
import org.junit.jupiter.api.*;
/**
* Tests the event cancellation mechanism of the event bus.
*
* @author Kai S. K. Engelbart
* @author Leon Hofmeister
* @since 0.1.0
*/
class CancelTest {
EventBus bus;
int hits;
/**
* Constructs an event bus and registers this test instance as an event listener.
*
* @since 0.1.0
*/
@BeforeEach
void registerListener() {
bus = new EventBus();
bus.registerListener(this);
}
/**
* Tests {@link EventBus#cancel()} with two event handlers, of which the first cancels the
* event.
*
* @since 0.1.0
*/
@Test
void testCancellation() {
bus.dispatch(new SimpleEvent());
assertEquals(1, hits);
}
@Event(SimpleEvent.class)
@Priority(100)
void onSimpleFirst() {
++hits;
bus.cancel();
}
@Event(SimpleEvent.class)
@Priority(50)
void onSimpleSecond() {
++hits;
}
}

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core/src/test/java/dev/kske/eventbus/core/DeadTest.java Normal file
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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 an endless recursion and should be logged instead.
*
* @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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core/src/test/java/dev/kske/eventbus/core/DispatchTest.java Normal file
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package dev.kske.eventbus.core;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.*;
/**
* Tests the dispatching mechanism of the event bus.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
*/
@Polymorphic
@Priority(150)
class DispatchTest {
EventBus bus;
/**
* Constructs an event bus and registers this test instance as an event listener.
*
* @since 0.0.1
*/
@BeforeEach
void registerListener() {
bus = new EventBus();
bus.registerListener(this);
bus.registerListener(SimpleEvent.class, e -> {
e.increment();
assertEquals(3, e.getCounter());
});
}
/**
* Tests {@link EventBus#dispatch(Object)} with multiple handler priorities, a polymorphic
* handler and a static handler.
*
* @since 0.0.1
*/
@Test
void testDispatch() {
bus.dispatch(new SimpleEventSub());
bus.dispatch(new SimpleEvent());
}
/**
* Tests {@link EventBus#debugExecutionOrder(Class)} based on the currently registered handlers.
*
* @since 1.2.0
*/
@Test
void testDebugExecutionOrder() {
assertEquals(
"Event handler execution order for class dev.kske.eventbus.core.SimpleEvent (3 handler(s)):\n"
+ "==========================================================================================\n"
+ "ReflectiveEventHandler[eventType=class dev.kske.eventbus.core.SimpleEvent, polymorphic=true, priority=200, method=void dev.kske.eventbus.core.DispatchTest.onSimpleEventFirst(dev.kske.eventbus.core.SimpleEvent), useParameter=true]\n"
+ "ReflectiveEventHandler[eventType=class dev.kske.eventbus.core.SimpleEvent, polymorphic=false, priority=150, method=static void dev.kske.eventbus.core.DispatchTest.onSimpleEventSecond(dev.kske.eventbus.core.SimpleEvent), useParameter=true]\n"
+ "CallbackEventHandler[eventType=class dev.kske.eventbus.core.SimpleEvent, polymorphic=false, priority=100]\n"
+ "==========================================================================================",
bus.debugExecutionOrder(SimpleEvent.class));
}
/**
* Tests whether the handlers bound to an event type are correct when retrieved from the binding
* cache. On the second call of {@link EventBus#debugExecutionOrder(Class)} the cache is used.
*
* @since 1.3.0
*/
@Test
void testBindingCache() {
assertEquals(bus.debugExecutionOrder(SimpleEventSub.class),
bus.debugExecutionOrder(SimpleEventSub.class));
}
@Event
@Priority(200)
void onSimpleEventFirst(SimpleEvent event) {
event.increment();
assertTrue(event.getCounter() == 1 || event.getCounter() == 2);
}
@Event
@Polymorphic(false)
static void onSimpleEventSecond(SimpleEvent event) {
event.increment();
assertEquals(2, event.getCounter());
}
}

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core/src/test/java/dev/kske/eventbus/core/ExceptionTest.java Normal file
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package dev.kske.eventbus.core;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.Test;
/**
* Tests the dispatching of an exception event if an event handler threw an exception.
*
* @author Kai S. K. Engelbart
* @since 1.1.0
*/
class ExceptionTest {
EventBus bus = new EventBus();
String event = "This event will cause an exception";
RuntimeException exception = new RuntimeException("I failed");
boolean exceptionEventHandled;
/**
* Tests exception event delivery.
*
* @since 1.1.0
*/
@Test
void testExceptionEvent() {
bus.registerListener(this);
bus.registerListener(new ExceptionListener());
bus.dispatch(event);
assertTrue(exceptionEventHandled);
bus.clearListeners();
}
/**
* Tests how the event bus reacts to an unhandled exception event. This should not lead to an
* exception or an endless recursion and should be logged instead.
*
* @since 1.1.0
*/
@Test
void testUnhandledExceptionEvent() {
bus.registerListener(this);
bus.dispatch(event);
bus.removeListener(this);
}
@Event(String.class)
void onString() {
throw exception;
}
class ExceptionListener {
@Event
void onExceptionEvent(ExceptionEvent exceptionEvent) {
assertEquals(bus, exceptionEvent.getEventBus());
assertEquals(event, exceptionEvent.getEvent());
assertEquals(exception, exceptionEvent.getCause());
exceptionEventHandled = true;
}
}
}

33
core/src/test/java/dev/kske/eventbus/core/ExceptionWrapperTest.java Normal file
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@ -0,0 +1,33 @@
package dev.kske.eventbus.core;
import static org.junit.jupiter.api.Assertions.assertThrows;
import org.junit.jupiter.api.Test;
/**
* Tests the behavior of the event bus when an {@link ExceptionWrapper} is thrown.
*
* @author Kai S. K. Engelbart
* @since 1.2.1
*/
class ExceptionWrapperTest {
EventBus bus = new EventBus();
String event = "This event will cause an exception";
/**
* Tests transparent rethrowing of an exception wrapper by {@link EventBus#dispatch(Object)}.
*
* @since 1.2.1
*/
@Test
void testExceptionWrapper() {
bus.registerListener(this);
assertThrows(ExceptionWrapper.class, () -> bus.dispatch(event));
}
@Event(String.class)
void onString() {
throw new ExceptionWrapper(new RuntimeException("I failed!"));
}
}

43
core/src/test/java/dev/kske/eventbus/core/InheritanceTest.java Normal file
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@ -0,0 +1,43 @@
package dev.kske.eventbus.core;
import static org.junit.jupiter.api.Assertions.assertSame;
import org.junit.jupiter.api.Test;
/**
* Tests whether event handlers correctly work in the context of an inheritance hierarchy. The
* effect of handler priorities is also accounted for.
*
* @author Kai S. K. Engelbart
* @since 1.3.0
*/
class InheritanceTest extends SimpleEventListenerBase implements SimpleEventListenerInterface {
EventBus bus = new EventBus();
@Test
void test() {
bus.registerListener(this);
var event = new SimpleEvent();
bus.dispatch(event);
assertSame(3, event.getCounter());
}
@Override
void onSimpleEventAbstractHandler(SimpleEvent event) {
assertSame(1, event.getCounter());
}
@Override
public void onSimpleEventInterfaceHandler(SimpleEvent event) {
event.increment();
}
@Event
@Priority(250)
private void onSimpleEventPrivate(SimpleEvent event) {
assertSame(0, event.getCounter());
event.increment();
}
}

73
core/src/test/java/dev/kske/eventbus/core/NestedTest.java Normal file
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@ -0,0 +1,73 @@
package dev.kske.eventbus.core;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.*;
/**
* Tests nested event dispatches.
*
* @author Kai S. K. Engelbart
* @since 1.2.0
*/
class NestedTest {
EventBus bus;
boolean nestedHit;
/**
* Constructs an event bus and registers this test instance as an event listener.
*
* @since 1.2.0
*/
@BeforeEach
void registerListener() {
bus = new EventBus();
bus.registerListener(this);
}
/**
* Dispatches a simple event, which should in turn cause a string to be dispatched as a nested
* event. If the corresponding handler sets {@link #nestedHit} to {@code true}, the test is
* successful.
*
* @since 1.2.0
*/
@Test
void testNestedDispatch() {
bus.dispatch(new SimpleEvent());
assertTrue(nestedHit);
}
/**
* Dispatches a string as a nested event and cancels the current dispatch afterwards.
*
* @since 1.2.0
*/
@Event(SimpleEvent.class)
void onSimpleEvent() {
bus.dispatch("Nested event");
bus.cancel();
}
/**
* Sets {@link #nestedHit} to {@code true} indicating that nested dispatches work.
*
* @since 1.2.0
*/
@Event(String.class)
void onString() {
nestedHit = true;
}
/**
* Fails the test if an exception is caused during the dispatch.
*
* @param e the event containing the exception
* @since 1.2.0
*/
@Event
void onException(ExceptionEvent e) {
fail("Exception during dispatch", e.getCause());
}
}

31
core/src/test/java/dev/kske/eventbus/core/SimpleEvent.java Normal file
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@ -0,0 +1,31 @@
package dev.kske.eventbus.core;
/**
* A simple event for testing purposes. The event contains a counter that is supposed to be
* incremented when the event is processed by a handler. That way it is possible to test whether all
* handlers that were supposed to be invoked were in fact invoked.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
*/
class SimpleEvent {
private int counter;
@Override
public String toString() {
return String.format("%s[%d]", getClass().getSimpleName(), counter);
}
void increment() {
++counter;
}
int getCounter() {
return counter;
}
void reset() {
counter = 0;
}
}

25
core/src/test/java/dev/kske/eventbus/core/SimpleEventListenerBase.java Normal file
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@ -0,0 +1,25 @@
package dev.kske.eventbus.core;
import static org.junit.jupiter.api.Assertions.*;
/**
* An abstract class defining a package-private and a private handler for {@link SimpleEvent}.
*
* @author Kai S. K. Engelbart
* @since 1.3.0
*/
@Priority(200)
abstract class SimpleEventListenerBase {
@Event
void onSimpleEventAbstractHandler(SimpleEvent event) {
fail("This handler should not be invoked");
}
@Event
@Priority(150)
private void onSimpleEventPrivate(SimpleEvent event) {
assertSame(1, event.getCounter());
event.increment();
}
}

14
core/src/test/java/dev/kske/eventbus/core/SimpleEventListenerInterface.java Normal file
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@ -0,0 +1,14 @@
package dev.kske.eventbus.core;
/**
* An interface defining a single handler for {@link SimpleEvent}.
*
* @author Kai S. K. Engelbart
* @since 1.3.0
*/
interface SimpleEventListenerInterface {
@Priority(120)
@Event
void onSimpleEventInterfaceHandler(SimpleEvent event);
}

9
core/src/test/java/dev/kske/eventbus/core/SimpleEventSub.java Normal file
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@ -0,0 +1,9 @@
package dev.kske.eventbus.core;
/**
* Subclass of {@link SimpleEvent} for testing purposes.
*
* @author Kai S. K. Engelbart
* @since 0.0.4
*/
class SimpleEventSub extends SimpleEvent {}

149
pom.xml
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@ -5,19 +5,27 @@
<groupId>dev.kske</groupId>
<artifactId>event-bus</artifactId>
<version>0.0.1</version>
<version>1.2.0</version>
<packaging>pom</packaging>
<name>Event Bus</name>
<description>An event handling framework for Java utilizing annotations.</description>
<url>https://git.kske.dev/zdm/event-bus</url>
<description>An event handling library for Java utilizing annotations.</description>
<url>https://git.kske.dev/kske/event-bus</url>
<modules>
<module>core</module>
<module>proc</module>
</modules>
<licenses>
<license>
<name>MIT License</name>
<url>http://www.opensource.org/licenses/mit-license.php</url>
<name>Apache License, Version 2.0</name>
<url>https://www.apache.org/licenses/LICENSE-2.0.txt</url>
<distribution>repo</distribution>
<comments>A business-friendly OSS license</comments>
</license>
</licenses>
<developers>
<developer>
<id>kske</id>
@ -31,10 +39,24 @@
<timezone>Europe/Berlin</timezone>
</developer>
</developers>
<contributors>
<contributor>
<name>Leon Hofmeister</name>
<email>leon@kske.dev</email>
<url>https://git.kske.dev/delvh</url>
<roles>
<role>qa</role>
<role>tester</role>
</roles>
<timezone>Europe/Berlin</timezone>
</contributor>
</contributors>
<scm>
<connection>scm:git:https://git.kske.dev/zdm/event-bus.git</connection>
<developerConnection>scm:git:ssh:git@git.kske.dev:zdm/event-bus.git</developerConnection>
<connection>scm:git:https://git.kske.dev/kske/event-bus.git</connection>
<developerConnection>scm:git:ssh://git@git.kske.dev:420/kske/event-bus.git</developerConnection>
<url>https://git.kske.dev/kske/event-bus</url>
</scm>
<properties>
@ -44,17 +66,100 @@
<maven.compiler.target>11</maven.compiler.target>
</properties>
<build>
<resources />
<testResources />
</build>
<!-- Configure deployment to OSSRH -->
<distributionManagement>
<snapshotRepository>
<id>ossrh</id>
<url>https://oss.sonatype.org/content/repositories/snapshots</url>
</snapshotRepository>
<repository>
<id>ossrh</id>
<url>https://oss.sonatype.org/service/local/staging/deploy/maven2/</url>
</repository>
</distributionManagement>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<version>5.6.2</version>
<scope>test</scope>
</dependency>
</dependencies>
</project>
<build>
<!-- Disable test resource folder -->
<testResources />
<plugins>
<!-- Support Java 9 modules -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
</plugin>
<!-- Attach sources to JAR -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-source-plugin</artifactId>
<version>3.2.1</version>
<executions>
<execution>
<id>attach-sources</id>
<goals>
<goal>jar</goal>
</goals>
</execution>
</executions>
</plugin>
<!-- Attach Javadoc to JAR -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-javadoc-plugin</artifactId>
<version>3.2.0</version>
<executions>
<execution>
<id>attach-javadocs</id>
<goals>
<goal>jar</goal>
</goals>
</execution>
</executions>
<!-- Support JDK-style Javadoc tags -->
<configuration>
<tags>
<tag>
<name>apiNote</name>
<placement>a</placement>
<head>API Note:</head>
</tag>
<tag>
<name>implSpec</name>
<placement>a</placement>
<head>Implementation Requirements:</head>
</tag>
<tag>
<name>implNote</name>
<placement>a</placement>
<head>Implementation Note:</head>
</tag>
</tags>
</configuration>
</plugin>
<!-- GPG sign JAR -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-gpg-plugin</artifactId>
<version>1.6</version>
<executions>
<execution>
<id>sign-artifacts</id>
<phase>verify</phase>
<goals>
<goal>sign</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

32
proc/.classpath Normal file
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@ -0,0 +1,32 @@
<?xml version="1.0" encoding="UTF-8"?>
<classpath>
<classpathentry kind="src" output="target/classes" path="src/main/java">
<attributes>
<attribute name="optional" value="true"/>
<attribute name="maven.pomderived" value="true"/>
</attributes>
</classpathentry>
<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-11">
<attributes>
<attribute name="maven.pomderived" value="true"/>
</attributes>
</classpathentry>
<classpathentry kind="con" path="org.eclipse.m2e.MAVEN2_CLASSPATH_CONTAINER">
<attributes>
<attribute name="maven.pomderived" value="true"/>
</attributes>
</classpathentry>
<classpathentry excluding="**" kind="src" output="target/classes" path="src/main/resources">
<attributes>
<attribute name="maven.pomderived" value="true"/>
</attributes>
</classpathentry>
<classpathentry kind="src" output="target/test-classes" path="src/test/java">
<attributes>
<attribute name="optional" value="true"/>
<attribute name="maven.pomderived" value="true"/>
<attribute name="test" value="true"/>
</attributes>
</classpathentry>
<classpathentry kind="output" path="target/classes"/>
</classpath>

23
proc/.project Normal file
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@ -0,0 +1,23 @@
<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
<name>event-bus-proc</name>
<comment></comment>
<projects>
</projects>
<buildSpec>
<buildCommand>
<name>org.eclipse.jdt.core.javabuilder</name>
<arguments>
</arguments>
</buildCommand>
<buildCommand>
<name>org.eclipse.m2e.core.maven2Builder</name>
<arguments>
</arguments>
</buildCommand>
</buildSpec>
<natures>
<nature>org.eclipse.jdt.core.javanature</nature>
<nature>org.eclipse.m2e.core.maven2Nature</nature>
</natures>
</projectDescription>

72
proc/pom.xml Normal file
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@ -0,0 +1,72 @@
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<artifactId>event-bus-proc</artifactId>
<name>Event Bus Annotation Processor</name>
<description>Annotation processor checking for errors related to the @Event annotation from Event Bus.</description>
<parent>
<groupId>dev.kske</groupId>
<artifactId>event-bus</artifactId>
<version>1.2.0</version>
</parent>
<dependencies>
<dependency>
<groupId>dev.kske</groupId>
<artifactId>event-bus-core</artifactId>
<version>${project.version}</version>
</dependency>
</dependencies>
<build>
<plugins>
<!-- Prevent annotation processing error during compilation -->
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<compilerArgument>-proc:none</compilerArgument>
</configuration>
</plugin>
<!-- Include event-bus-core classes into JAR -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>3.2.4</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<minimizeJar>true</minimizeJar>
<filters>
<filter>
<artifact>dev.kske:event-bus-core</artifact>
<excludes>
<exclude>META-INF/MANIFEST.MF</exclude>
</excludes>
</filter>
<filter>
<artifact>*:*</artifact>
<excludes>
<exclude>module-info.class</exclude>
<exclude>META-INF/maven/**</exclude>
</excludes>
</filter>
</filters>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

147
proc/src/main/java/dev/kske/eventbus/proc/EventProcessor.java Normal file
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@ -0,0 +1,147 @@
package dev.kske.eventbus.proc;
import java.util.Set;
import javax.annotation.processing.*;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.*;
import javax.lang.model.type.*;
import javax.tools.Diagnostic.Kind;
import dev.kske.eventbus.core.*;
/**
* This annotation processor checks event handlers for common mistakes which can only be detected
* during runtime otherwise.
*
* @author Kai S. K. Engelbart
* @since 1.0.0
*/
@SupportedAnnotationTypes("dev.kske.eventbus.core.Event")
@SupportedSourceVersion(SourceVersion.RELEASE_11)
public class EventProcessor extends AbstractProcessor {
@SuppressWarnings("unchecked")
@Override
public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
if (!roundEnv.errorRaised() && !roundEnv.processingOver())
processRound(
(Set<ExecutableElement>) roundEnv.getElementsAnnotatedWith(Event.class));
// Do not claim the processed annotations
return false;
}
private void processRound(Set<ExecutableElement> eventHandlers) {
for (ExecutableElement eventHandler : eventHandlers) {
Event eventAnnotation = eventHandler.getAnnotation(Event.class);
TypeMirror eventType;
// Determine the event type and how it is defined
boolean useParameter;
try {
eventAnnotation.value();
throw new EventBusException(
"Could not determine event type of handler " + eventHandler);
} catch (MirroredTypeException e) {
// Task failed successfully
eventType = e.getTypeMirror();
useParameter = eventType.getKind() == TypeKind.VOID;
}
// Check handler signature
boolean pass = false;
if (useParameter && eventHandler.getParameters().isEmpty())
error(eventHandler, "The method or the annotation must define the event type");
else if (!useParameter && eventHandler.getParameters().size() == 1)
error(eventHandler,
"Either the method or the annotation must define the event type");
else if (eventHandler.getParameters().size() > 1)
error(eventHandler, "Method must not have more than one parameter");
else
pass = true;
// Warn the user about unused return values
if (useParameter && eventHandler.getReturnType().getKind() != TypeKind.VOID)
warning(eventHandler, "Unused return value");
// Abort checking if the handler signature is incorrect
if (!pass)
continue;
// Additional checks if parameter is used
if (useParameter) {
VariableElement paramElement = eventHandler.getParameters().get(0);
eventType = paramElement.asType();
// Check if parameter is object
// Abort checking otherwise
if (eventType.getKind() != TypeKind.DECLARED) {
error(paramElement, "Event must be an object");
continue;
}
}
// Get the listener containing this handler
TypeElement listener = (TypeElement) eventHandler.getEnclosingElement();
// Default properties
boolean defPolymorphic = false;
int defPriority = 100;
// Listener-level polymorphism
Polymorphic listenerPolymorphic = listener.getAnnotation(Polymorphic.class);
boolean hasListenerPolymorphic = listenerPolymorphic != null;
// Listener-level priority
Priority listenerPriority = listener.getAnnotation(Priority.class);
boolean hasListenerPriority = listenerPriority != null;
// Effective polymorphism
boolean polymorphic =
hasListenerPolymorphic ? listenerPolymorphic.value() : defPolymorphic;
boolean hasHandlerPolymorphic = eventHandler.getAnnotation(Polymorphic.class) != null;
if (hasHandlerPolymorphic)
polymorphic = eventHandler.getAnnotation(Polymorphic.class).value();
// Effective priority
int priority =
hasListenerPriority ? listenerPriority.value() : defPriority;
boolean hasHandlerPriority = eventHandler.getAnnotation(Priority.class) != null;
if (hasHandlerPriority)
priority = eventHandler.getAnnotation(Priority.class).value();
// Detect useless polymorphism redefinition
if (hasListenerPolymorphic && hasHandlerPolymorphic
&& listenerPolymorphic.value() == polymorphic)
warning(eventHandler, "@Polymorphism is already defined at listener level");
// Detect useless priority redefinition
if (hasListenerPriority && hasHandlerPriority && listenerPriority.value() == priority)
warning(eventHandler, "@Priority is already defined at the listener level");
// Detect missing or useless @Polymorphic
Element eventElement = ((DeclaredType) eventType).asElement();
// Check for handlers for abstract types that aren't polymorphic
if (!polymorphic && (eventElement.getKind() == ElementKind.INTERFACE
|| eventElement.getModifiers().contains(Modifier.ABSTRACT)))
warning(eventHandler,
"Parameter should be instantiable or handler should use @Polymorphic");
// Check for handlers for final types that are polymorphic
else if (polymorphic && eventElement.getModifiers().contains(Modifier.FINAL))
warning(eventHandler,
"@Polymorphic should be removed as parameter cannot be subclassed");
}
}
private void warning(Element e, String msg, Object... args) {
processingEnv.getMessager().printMessage(Kind.WARNING, String.format(msg, args), e);
}
private void error(Element e, String msg, Object... args) {
processingEnv.getMessager().printMessage(Kind.ERROR, String.format(msg, args), e);
}
}

7
proc/src/main/java/dev/kske/eventbus/proc/package-info.java Normal file
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@ -0,0 +1,7 @@
/**
* Contains the Event Bus annotation processor.
*
* @author Kai S. K. Engelbart
* @since 1.0.0
*/
package dev.kske.eventbus.proc;

12
proc/src/main/java/module-info.java Normal file
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@ -0,0 +1,12 @@
/**
* Contains an annotation processor for checking for errors related to the
* {@link dev.kske.eventbus.core.Event} annotation from Event Bus.
*
* @author Kai S. K. Engelbart
* @since 1.0.0
*/
module dev.kske.eventbus.proc {
requires java.compiler;
requires dev.kske.eventbus.core;
}

1
proc/src/main/resources/META-INF/services/javax.annotation.processing.Processor Normal file
View File

@ -0,0 +1 @@
dev.kske.eventbus.proc.EventProcessor

34
src/main/java/dev/kske/eventbus/Event.java
View File

@ -1,34 +0,0 @@
package dev.kske.eventbus;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.*;
/**
* Indicates that a method is an event handler. To be successfully used as such, the method has to
* comply with the following specifications:
* <ul>
* <li>Declared inside a class that implements {@link EventListener}</li>
* <li>One parameter of a type that implements {@link IEvent}</li>
* <li>Return type of {@code void}</li>
* </ul>
*
* @author Kai S. K. Engelbart
* @since 0.0.1
*/
@Documented
@Retention(RUNTIME)
@Target(METHOD)
public @interface Event {
/**
* Defines the priority of the event handler. Handlers are executed in descending order of their
* priority.
* <p>
* The execution order of handlers with the same priority is undefined.
*
* @since 0.0.1
*/
int priority() default 100;
}

120
src/main/java/dev/kske/eventbus/EventBus.java
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@ -1,120 +0,0 @@
package dev.kske.eventbus;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
/**
* Event listeners can be registered at an event bus to be notified when an event is dispatched.
* <p>
* This is a thread-safe implementation.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
* @see Event
*/
public final class EventBus {
private final Map<Class<? extends IEvent>, Collection<EventHandler>> bindings
= new ConcurrentHashMap<>();
private final Set<EventListener> registeredListeners = ConcurrentHashMap.newKeySet();
/**
* Dispatches an event to all event handlers registered for it in descending order of their
* priority.
*
* @param event the event to dispatch
* @since 0.0.1
*/
public void dispatch(IEvent event) {
getHandlersFor(event.getClass()).forEach(handler -> handler.execute(event));
}
/**
* Searches for the event handlers bound to an event class.
*
* @param eventClass the event class to use for the search
* @return all event handlers registered for the event class
* @since 0.0.1
*/
private List<EventHandler> getHandlersFor(Class<? extends IEvent> eventClass) {
return bindings.containsKey(eventClass) ? new ArrayList<>(bindings.get(eventClass))
: new ArrayList<>();
}
/**
* Registers an event listener at this event bus.
*
* @param listener the listener to register
* @throws EventBusException if the listener is already registered or a declared event handler
* does not comply to the specification
* @since 0.0.1
* @see Event
*/
public void registerListener(EventListener listener) throws EventBusException {
if (registeredListeners.contains(listener))
throw new EventBusException(listener + " already registered!");
registeredListeners.add(listener);
for (var method : listener.getClass().getDeclaredMethods()) {
Event annotation = method.getAnnotation(Event.class);
// Skip methods without annotations
if (annotation == null)
continue;
// Check for correct method signature and return type
if (method.getParameterCount() != 1)
throw new EventBusException(method + " does not have an argument count of 1!");
if (!method.getReturnType().equals(void.class))
throw new EventBusException(method + " does not have a return type of void!");
var param = method.getParameterTypes()[0];
if (!IEvent.class.isAssignableFrom(param))
throw new EventBusException(param + " is not of type IEvent!");
@SuppressWarnings("unchecked")
var realParam = (Class<? extends IEvent>) param;
if (!bindings.containsKey(realParam))
bindings.put(realParam, new TreeSet<>());
bindings.get(realParam).add(new EventHandler(listener, method, annotation));
}
}
/**
* Removes a specific listener from this event bus.
*
* @param listener the listener to remove
* @since 0.0.1
*/
public void removeListener(EventListener listener) {
for (var binding : bindings.values()) {
var it = binding.iterator();
while (it.hasNext())
if (it.next().getListener() == listener)
it.remove();
}
registeredListeners.remove(listener);
}
/**
* Removes all event listeners from this event bus.
*
* @since 0.0.1
*/
public void clearListeners() {
bindings.clear();
registeredListeners.clear();
}
/**
* Provides an unmodifiable view of the event listeners registered at this event bus.
*
* @return all registered event listeners
* @since 0.0.1
*/
public Set<EventListener> getRegisteredListeners() {
return Collections.unmodifiableSet(registeredListeners);
}
}

21
src/main/java/dev/kske/eventbus/EventBusException.java
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@ -1,21 +0,0 @@
package dev.kske.eventbus;
/**
* This runtime exception is thrown when an event bus error occurs. This can either occur while
* registering event listeners with invalid handlers, or when an event handler throws an exception.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
*/
public class EventBusException extends RuntimeException {
private static final long serialVersionUID = 1L;
public EventBusException(String message, Throwable cause) {
super(message, cause);
}
public EventBusException(String message) {
super(message);
}
}

84
src/main/java/dev/kske/eventbus/EventHandler.java
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@ -1,84 +0,0 @@
package dev.kske.eventbus;
import java.lang.reflect.*;
/**
* Internal representation of an event handling method.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
* @see EventBus
*/
final class EventHandler implements Comparable<EventHandler> {
private final EventListener listener;
private final Method method;
private final Event annotation;
/**
* Constructs an event handler.
*
* @param listener the listener containing the handler
* @param method the handler method
* @param annotation the event annotation
* @since 0.0.1
*/
EventHandler(EventListener listener, Method method, Event annotation) {
this.listener = listener;
this.method = method;
this.annotation = annotation;
}
/**
* Compares this to another event handler based on {@link Event#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 the correct order from a tree set.
*
* @since 0.0.1
*/
@Override
public int compareTo(EventHandler other) {
int priority = other.annotation.priority() - annotation.priority();
if (priority == 0)
priority = listener.hashCode() - other.listener.hashCode();
return priority == 0 ? hashCode() - other.hashCode() : priority;
}
/**
* Executes the event handler.
*
* @param event the event used as the method parameter
* @throws EventBusException if the handler throws an exception
* @since 0.0.1
*/
void execute(IEvent event) throws EventBusException {
try {
method.invoke(listener, event);
} catch (
IllegalAccessException
| IllegalArgumentException
| InvocationTargetException e
) {
throw new EventBusException("Failed to invoke event handler!", e);
}
}
/**
* @return the listener containing this handler
* @since 0.0.1
*/
EventListener getListener() { return listener; }
/**
* @return the event annotation
* @since 0.0.1
*/
Event getAnnotation() { return annotation; }
/**
* @return the priority of the event annotation
* @since 0.0.1
*/
int getPriority() { return annotation.priority(); }
}

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src/main/java/dev/kske/eventbus/EventListener.java
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package dev.kske.eventbus;
/**
* Marker interface for event listeners. Event listeners can contain event handling methods to which
* events can be dispatched.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
* @see Event
* @see EventBus
*/
public interface EventListener {}

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src/main/java/dev/kske/eventbus/IEvent.java
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package dev.kske.eventbus;
/**
* Marker interface for event objects. Event objects can be used as event handler parameters and
* thus can be dispatched to the event bus.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
* @see Event
* @see EventBus
*/
public interface IEvent {}

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src/main/java/dev/kske/eventbus/package-info.java
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/**
* Contains the public API and implementation of the event bus library.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
* @see dev.kske.eventbus.Event
* @see dev.kske.eventbus.EventBus
*/
package dev.kske.eventbus;

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src/test/java/dev/kske/eventbus/EventBusTest.java
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package dev.kske.eventbus;
import static org.junit.jupiter.api.Assertions.assertEquals;
import org.junit.jupiter.api.*;
/**
* Tests the of the event bus library.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
*/
class EventBusTest implements EventListener {
public EventBus eventBus = new EventBus();
int hits;
@BeforeEach
public void registerListener() {
eventBus.registerListener(this);
}
@Test
void testDispatch() {
eventBus.dispatch(new SimpleEvent());
}
@Event(priority = 50)
public void onSimpleEventSecond(SimpleEvent event) {
++hits;
assertEquals(2, hits);
}
@Event(priority = 150)
public void onSimpleEventFirst(SimpleEvent event) {
++hits;
assertEquals(1, hits);
}
}

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src/test/java/dev/kske/eventbus/SimpleEvent.java
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package dev.kske.eventbus;
/**
* A simple event for testing purposes.
*
* @author Kai S. K. Engelbart
* @since 0.0.1
*/
public class SimpleEvent implements IEvent {}