Moved event classes to envoy-common

src/main/java/envoy/data/TextMessage.java

@@ -41,7 +41,7 @@ public class TextMessage extends Message {
 				getId(),
 				getSender(),
 				getRecipient(),
-				new SimpleDateFormat("dd.MM.yyyy hh:mm:ss").format(getDate()),
+				new SimpleDateFormat("dd.MM.yyyy HH:mm:ss").format(getDate()),
 				getStatus(),
 				content);
 	}

src/main/java/envoy/event/Event.java

@@ -0,0 +1,19 @@
+package envoy.event;
+
+/**
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>Event.java</strong><br>
+ * Created: <strong>04.12.2019</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @param <T> the type of the Event
+ * @since Envoy v0.2-alpha
+ */
+public interface Event<T> {
+
+	/**
+	 * @return the data associated with this event
+	 */
+	T get();
+}
+

src/main/java/envoy/event/EventBus.java

@@ -0,0 +1,81 @@
+package envoy.event;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * This class handles events by allowing {@link EventHandler} object to register
+ * themselves and then be notified about certain events dispatched by the event
+ * bus.<br>
+ * <br>
+ * The event bus is a singleton and can be used across the entire application to
+ * guarantee the propagation of events.<br>
+ *
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>EventBus.java</strong><br>
+ * Created: <strong>04.12.2019</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy v0.2-alpha
+ */
+public class EventBus {
+
+	/**
+	 * Contains all {@link EventHandler} instances registered at this
+	 * {@link EventBus} as values mapped to by their supported {@link Event}
+	 * classes.
+	 */
+	private Map<Class<? extends Event<?>>, List<EventHandler>> handlers = new HashMap<>();
+
+	/**
+	 * The singleton instance of this {@link EventBus} that is used across the
+	 * entire application.
+	 */
+	private static EventBus eventBus = new EventBus();
+
+	/**
+	 * This constructor is not accessible from outside this class because a
+	 * singleton instance of it is provided by the {@link EventBus#getInstance()}
+	 * method.
+	 */
+	private EventBus() {}
+
+	/**
+	 * @return the singleton instance of the {@link EventBus}
+	 * @since Envoy v0.2-alpha
+	 */
+	public static EventBus getInstance() { return eventBus; }
+
+	/**
+	 * Registers an {@link EventHandler} to be notified when a
+	 * {@link Event} of a certain type is dispatched.
+	 *
+	 * @param eventClass the class which the {@link EventHandler} is subscribed to
+	 * @param handler    the {@link EventHandler} to register
+	 * @since Envoy v0.2-alpha
+	 */
+	public void register(Class<? extends Event<?>> eventClass, EventHandler handler) {
+		if (!handlers.containsKey(eventClass)) handlers.put(eventClass, new ArrayList<>());
+		handlers.get(eventClass).add(handler);
+	}
+
+	/**
+	 * Dispatches a {@link Event} to every {@link EventHandler} subscribed to it.
+	 *
+	 * @param event the {@link Event} to dispatch
+	 * @since Envoy v0.2-alpha
+	 */
+	public void dispatch(Event<?> event) {
+		handlers.keySet().stream().filter(event.getClass()::isAssignableFrom).map(handlers::get).flatMap(List::stream).forEach(h -> h.handle(event));
+	}
+
+	/**
+	 * @return a map of all {@link EventHandler} instances currently registered at
+	 *         this {@link EventBus} with the {@link Event} classes they are
+	 *         subscribed to as keys
+	 * @since Envoy v0.2-alpha
+	 */
+	public Map<Class<? extends Event<?>>, List<EventHandler>> getHandlers() { return handlers; }
+}

src/main/java/envoy/event/EventHandler.java

@@ -0,0 +1,18 @@
+package envoy.event;
+
+/**
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>EventHandler.java</strong><br>
+ * Created: <strong>04.12.2019</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ */
+public interface EventHandler {
+
+	/**
+	 * Consumes an event dispatched by the event bus.
+	 *
+	 * @param event The event dispatched by the event bus, only of supported type
+	 */
+	void handle(Event<?> event);
+}

src/main/java/envoy/event/MessageEvent.java

@@ -0,0 +1,27 @@
+package envoy.event;
+
+import envoy.data.Message;
+
+/**
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>MessageCreationEvent.java</strong><br>
+ * Created: <strong>4 Dec 2019</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ */
+public class MessageEvent implements Event<Message> {
+
+	protected final Message message;
+
+	/**
+	 * Initializes a {@link MessageEvent} conveying information about a
+	 * {@link Message} object.
+	 *
+	 * @param message the {@link Message} object to attach to this event
+	 * @since Envoy v0.2-alpha
+	 */
+	public MessageEvent(Message message) { this.message = message; }
+
+	@Override
+	public Message get() { return message; }
+}