New event publishing mechanism with Consumer<T> #327

modules/global/src/com/haulmont/bali/events/EventPublisher.java

@@ -0,0 +1,157 @@
+/*
+ * Copyright (c) 2008-2018 Haulmont.
+ *
+ * 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
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.
+ */
+
+package com.haulmont.bali.events;
+
+import javax.annotation.concurrent.NotThreadSafe;
+import java.util.ArrayList;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Consumer;
+
+/**
+ * EventPublisher class implementing the event listening model with concrete event classes.
+ */
+@NotThreadSafe
+public class EventPublisher {
+    protected static final int EVENTS_MAP_EXPECTED_MAX_SIZE = 4;
+    protected static final int EVENTS_LIST_INITIAL_CAPACITY = 2;
+
+    // Map with listener classes and listener lists
+    // Lists are created on demand
+    protected Map<Class, List<Consumer>> events = null;
+
+    /**
+     * Add an event listener for events with type T.
+     *
+     * @param eventType event class
+     * @param listener  listener
+     * @param <T>       type of event
+     * @return registration object
+     */
+    public <T> Subscription subscribe(Class<T> eventType, Consumer<T> listener) {
+        if (eventType == null) {
+            throw new IllegalArgumentException("eventType cannot be null");
+        }
+        if (listener == null) {
+            throw new IllegalArgumentException("listener cannot be null");
+        }
+
+        if (events == null) {
+            events = new IdentityHashMap<>(EVENTS_MAP_EXPECTED_MAX_SIZE);
+        }
+
+        List<Consumer> listeners = events.computeIfAbsent(eventType,
+                eventClass -> new ArrayList<>(EVENTS_LIST_INITIAL_CAPACITY));
+        if (!listeners.contains(listener)) {
+            listeners.add(listener);
+        }
+
+        return new SubscriptionImpl<>(this, eventType, listener);
+    }
+
+    /**
+     * Remove an event listener for events with type T.
+     *
+     * @param eventType event class
+     * @param listener  listener
+     * @param <T>       type of event
+     * @return true if listener has been removed
+     */
+    public <T> boolean unsubscribe(Class<T> eventType, Consumer<T> listener) {
+        if (eventType == null) {
+            throw new IllegalArgumentException("eventType cannot be null");
+        }
+        if (listener == null) {
+            throw new IllegalArgumentException("listener cannot be null");
+        }
+
+        if (events != null) {
+            List<Consumer> listenersList = events.get(eventType);
+            if (listenersList != null) {
+                boolean wasRemoved = listenersList.remove(listener);
+                if (listenersList.isEmpty()) {
+                    events.remove(eventType);
+                }
+                return wasRemoved;
+            }
+            return false;
+        }
+        return false;
+    }
+
+    /**
+     * Check if there are listeners for event type T.
+     *
+     * @param eventType event class
+     * @param <T>       type of event
+     * @return true if there are one or more listeners for type T
+     */
+    public <T> boolean hasListeners(Class<T> eventType) {
+        if (eventType == null) {
+            throw new IllegalArgumentException("eventType cannot be null");
+        }
+
+        return events != null
+                && events.get(eventType) != null;
+    }
+
+    /**
+     * Fire listeners for event type T.
+     *
+     * @param eventType event class
+     * @param event     event object
+     * @param <T>       type of event
+     */
+    public <T> void publish(Class<T> eventType, T event) {
+        if (eventType == null) {
+            throw new IllegalArgumentException("eventType cannot be null");
+        }
+        if (event == null) {
+            throw new IllegalArgumentException("event cannot be null");
+        }
+
+        if (events != null) {
+            @SuppressWarnings("unchecked")
+            List<Consumer> listeners = events.get(eventType);
+            if (listeners != null) {
+                for (Object listenerEntry : listeners.toArray()) {
+                    @SuppressWarnings("unchecked")
+                    Consumer<T> listener = (Consumer<T>) listenerEntry;
+                    listener.accept(event);
+                }
+            }
+        }
+    }
+
+    protected static class SubscriptionImpl<T> implements Subscription {
+        protected EventPublisher router;
+        protected Class<T> eventClass;
+        protected Consumer<T> listener;
+
+        public SubscriptionImpl(EventPublisher router, Class<T> eventClass, Consumer<T> listener) {
+            this.router = router;
+            this.eventClass = eventClass;
+            this.listener = listener;
+        }
+
+        @Override
+        public void remove() {
+            router.unsubscribe(eventClass, listener);
+        }
+    }
+}

modules/global/src/com/haulmont/bali/events/Subscription.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2008-2018 Haulmont.
+ *
+ * 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
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.
+ */
+
+package com.haulmont.bali.events;
+
+/**
+ * A registration object for removing an event listener added to a source.
+ */
+public interface Subscription {
+    /**
+     * Removes the associated listener from the event source.
+     */
+    void remove();
+}