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