001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.commons.configuration2.event; 018 019import java.util.Collections; 020import java.util.HashMap; 021import java.util.Iterator; 022import java.util.LinkedList; 023import java.util.List; 024import java.util.Map; 025import java.util.NoSuchElementException; 026import java.util.Set; 027import java.util.concurrent.CopyOnWriteArrayList; 028 029/** 030 * <p> 031 * A class for managing event listeners for an event source. 032 * </p> 033 * <p> 034 * This class allows registering an arbitrary number of event listeners for specific event types. Event types are 035 * specified using the {@link EventType} class. Due to the type parameters in method signatures, it is guaranteed that 036 * registered listeners are compatible with the event types they are interested in. 037 * </p> 038 * <p> 039 * There are also methods for firing events. Here all registered listeners are determined - based on the event type 040 * specified at registration time - which should receive the event to be fired. So basically, the event type at listener 041 * registration serves as a filter criterion. Because of the hierarchical nature of event types it can be determined in 042 * a fine-grained way which events are propagated to which listeners. It is also possible to register a listener 043 * multiple times for different event types. 044 * </p> 045 * <p> 046 * Implementation note: This class is thread-safe. 047 * </p> 048 * 049 * @since 2.0 050 */ 051public class EventListenerList { 052 /** A list with the listeners added to this object. */ 053 private final List<EventListenerRegistrationData<?>> listeners; 054 055 /** 056 * Creates a new instance of {@code EventListenerList}. 057 */ 058 public EventListenerList() { 059 listeners = new CopyOnWriteArrayList<>(); 060 } 061 062 /** 063 * Adds an event listener for the specified event type. This listener is notified about events of this type and all its 064 * sub types. 065 * 066 * @param type the event type (must not be <b>null</b>) 067 * @param listener the listener to be registered (must not be <b>null</b>) 068 * @param <T> the type of events processed by this listener 069 * @throws IllegalArgumentException if a required parameter is <b>null</b> 070 */ 071 public <T extends Event> void addEventListener(final EventType<T> type, final EventListener<? super T> listener) { 072 listeners.add(new EventListenerRegistrationData<>(type, listener)); 073 } 074 075 /** 076 * Adds the specified listener registration data object to the internal list of event listeners. This is an alternative 077 * registration method; the event type and the listener are passed as a single data object. 078 * 079 * @param regData the registration data object (must not be <b>null</b>) 080 * @param <T> the type of events processed by this listener 081 * @throws IllegalArgumentException if the registration data object is <b>null</b> 082 */ 083 public <T extends Event> void addEventListener(final EventListenerRegistrationData<T> regData) { 084 if (regData == null) { 085 throw new IllegalArgumentException("EventListenerRegistrationData must not be null!"); 086 } 087 listeners.add(regData); 088 } 089 090 /** 091 * Removes the event listener registration for the given event type and listener. An event listener instance may be 092 * registered multiple times for different event types. Therefore, when removing a listener the event type of the 093 * registration in question has to be specified. The return value indicates whether a registration was removed. A value 094 * of <b>false</b> means that no such combination of event type and listener was found. 095 * 096 * @param eventType the event type 097 * @param listener the event listener to be removed 098 * @param <T> the type of events processed by this listener 099 * @return a flag whether a listener registration was removed 100 */ 101 public <T extends Event> boolean removeEventListener(final EventType<T> eventType, final EventListener<? super T> listener) { 102 return !(listener == null || eventType == null) && removeEventListener(new EventListenerRegistrationData<>(eventType, listener)); 103 } 104 105 /** 106 * Removes the event listener registration defined by the passed in data object. This is an alternative method for 107 * removing a listener which expects the event type and the listener in a single data object. 108 * 109 * @param regData the registration data object 110 * @param <T> the type of events processed by this listener 111 * @return a flag whether a listener registration was removed 112 * @see #removeEventListener(EventType, EventListener) 113 */ 114 public <T extends Event> boolean removeEventListener(final EventListenerRegistrationData<T> regData) { 115 return listeners.remove(regData); 116 } 117 118 /** 119 * Fires an event to all registered listeners matching the event type. 120 * 121 * @param event the event to be fired (must not be <b>null</b>) 122 * @throws IllegalArgumentException if the event is <b>null</b> 123 */ 124 public void fire(final Event event) { 125 if (event == null) { 126 throw new IllegalArgumentException("Event to be fired must not be null!"); 127 } 128 129 for (final EventListenerIterator<? extends Event> iterator = getEventListenerIterator(event.getEventType()); iterator.hasNext();) { 130 iterator.invokeNextListenerUnchecked(event); 131 } 132 } 133 134 /** 135 * Gets an {@code Iterable} allowing access to all event listeners stored in this list which are compatible with the 136 * specified event type. 137 * 138 * @param eventType the event type object 139 * @param <T> the event type 140 * @return an {@code Iterable} with the selected event listeners 141 */ 142 public <T extends Event> Iterable<EventListener<? super T>> getEventListeners(final EventType<T> eventType) { 143 return () -> getEventListenerIterator(eventType); 144 } 145 146 /** 147 * Gets a specialized iterator for obtaining all event listeners stored in this list which are compatible with the 148 * specified event type. 149 * 150 * @param eventType the event type object 151 * @param <T> the event type 152 * @return an {@code Iterator} with the selected event listeners 153 */ 154 public <T extends Event> EventListenerIterator<T> getEventListenerIterator(final EventType<T> eventType) { 155 return new EventListenerIterator<>(listeners.iterator(), eventType); 156 } 157 158 /** 159 * Gets an (unmodifiable) list with registration information about all event listeners registered at this object. 160 * 161 * @return a list with event listener registration information 162 */ 163 public List<EventListenerRegistrationData<?>> getRegistrations() { 164 return Collections.unmodifiableList(listeners); 165 } 166 167 /** 168 * Gets a list with {@code EventListenerRegistrationData} objects for all event listener registrations of the 169 * specified event type or an event type having this type as super type (directly or indirectly). Note that this is the 170 * opposite direction than querying event types for firing events: in this case event listener registrations are 171 * searched which are super event types from a given type. This method in contrast returns event listener registrations 172 * for listeners that extend a given super type. 173 * 174 * @param eventType the event type object 175 * @param <T> the event type 176 * @return a list with the matching event listener registration objects 177 */ 178 public <T extends Event> List<EventListenerRegistrationData<? extends T>> getRegistrationsForSuperType(final EventType<T> eventType) { 179 final Map<EventType<?>, Set<EventType<?>>> superTypes = new HashMap<>(); 180 final List<EventListenerRegistrationData<? extends T>> results = new LinkedList<>(); 181 182 listeners.forEach(reg -> { 183 Set<EventType<?>> base = superTypes.get(reg.getEventType()); 184 if (base == null) { 185 base = EventType.fetchSuperEventTypes(reg.getEventType()); 186 superTypes.put(reg.getEventType(), base); 187 } 188 if (base.contains(eventType)) { 189 @SuppressWarnings("unchecked") 190 final 191 // This is safe because we just did a check 192 EventListenerRegistrationData<? extends T> result = (EventListenerRegistrationData<? extends T>) reg; 193 results.add(result); 194 } 195 }); 196 197 return results; 198 } 199 200 /** 201 * Removes all event listeners registered at this object. 202 */ 203 public void clear() { 204 listeners.clear(); 205 } 206 207 /** 208 * Adds all event listener registrations stored in the specified {@code EventListenerList} to this list. 209 * 210 * @param c the list to be copied (must not be <b>null</b>) 211 * @throws IllegalArgumentException if the list to be copied is <b>null</b> 212 */ 213 public void addAll(final EventListenerList c) { 214 if (c == null) { 215 throw new IllegalArgumentException("List to be copied must not be null!"); 216 } 217 c.getRegistrations().forEach(this::addEventListener); 218 } 219 220 /** 221 * Helper method for calling an event listener with an event. We have to operate on raw types to make this code compile. 222 * However, this is safe because of the way the listeners have been registered and associated with event types - so it 223 * is ensured that the event is compatible with the listener. 224 * 225 * @param listener the event listener to be called 226 * @param event the event to be fired 227 */ 228 @SuppressWarnings("unchecked") 229 private static void callListener(final EventListener<?> listener, final Event event) { 230 @SuppressWarnings("rawtypes") 231 final EventListener rowListener = listener; 232 rowListener.onEvent(event); 233 } 234 235 /** 236 * A special {@code Iterator} implementation used by the {@code getEventListenerIterator()} method. This iterator 237 * returns only listeners compatible with a specified event type. It has a convenience method for invoking the current 238 * listener in the iteration with an event. 239 * 240 * @param <T> the event type 241 */ 242 public static final class EventListenerIterator<T extends Event> implements Iterator<EventListener<? super T>> { 243 /** The underlying iterator. */ 244 private final Iterator<EventListenerRegistrationData<?>> underlyingIterator; 245 246 /** The base event type. */ 247 private final EventType<T> baseEventType; 248 249 /** The set with accepted event types. */ 250 private final Set<EventType<?>> acceptedTypes; 251 252 /** The next element in the iteration. */ 253 private EventListener<? super T> nextElement; 254 255 private EventListenerIterator(final Iterator<EventListenerRegistrationData<?>> it, final EventType<T> base) { 256 underlyingIterator = it; 257 baseEventType = base; 258 acceptedTypes = EventType.fetchSuperEventTypes(base); 259 initNextElement(); 260 } 261 262 @Override 263 public boolean hasNext() { 264 return nextElement != null; 265 } 266 267 @Override 268 public EventListener<? super T> next() { 269 if (nextElement == null) { 270 throw new NoSuchElementException("No more event listeners!"); 271 } 272 273 final EventListener<? super T> result = nextElement; 274 initNextElement(); 275 return result; 276 } 277 278 /** 279 * Obtains the next event listener in this iteration and invokes it with the given event object. 280 * 281 * @param event the event object 282 * @throws NoSuchElementException if iteration is at its end 283 */ 284 public void invokeNext(final Event event) { 285 validateEvent(event); 286 invokeNextListenerUnchecked(event); 287 } 288 289 /** 290 * {@inheritDoc} This implementation always throws an exception. Removing elements is not supported. 291 */ 292 @Override 293 public void remove() { 294 throw new UnsupportedOperationException("Removing elements is not supported!"); 295 } 296 297 /** 298 * Determines the next element in the iteration. 299 */ 300 private void initNextElement() { 301 nextElement = null; 302 while (underlyingIterator.hasNext() && nextElement == null) { 303 final EventListenerRegistrationData<?> regData = underlyingIterator.next(); 304 if (acceptedTypes.contains(regData.getEventType())) { 305 nextElement = castListener(regData); 306 } 307 } 308 } 309 310 /** 311 * Checks whether the specified event can be passed to an event listener in this iteration. This check is done via the 312 * hierarchy of event types. 313 * 314 * @param event the event object 315 * @throws IllegalArgumentException if the event is invalid 316 */ 317 private void validateEvent(final Event event) { 318 if (event == null || !EventType.fetchSuperEventTypes(event.getEventType()).contains(baseEventType)) { 319 throw new IllegalArgumentException("Event incompatible with listener iteration: " + event); 320 } 321 } 322 323 /** 324 * Invokes the next event listener in the iteration without doing a validity check on the event. This method is called 325 * internally to avoid duplicate event checks. 326 * 327 * @param event the event object 328 */ 329 private void invokeNextListenerUnchecked(final Event event) { 330 callListener(next(), event); 331 } 332 333 /** 334 * Extracts the listener from the given data object and performs a cast to the target type. This is safe because it has 335 * been checked before that the type is compatible. 336 * 337 * @param regData the data object 338 * @return the extracted listener 339 */ 340 @SuppressWarnings("unchecked") 341 private EventListener<? super T> castListener(final EventListenerRegistrationData<?> regData) { 342 @SuppressWarnings("rawtypes") 343 final EventListener listener = regData.getListener(); 344 return listener; 345 } 346 } 347}