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 */ 017 018package org.apache.commons.lang3.event; 019 020import java.io.ByteArrayOutputStream; 021import java.io.IOException; 022import java.io.ObjectInputStream; 023import java.io.ObjectOutputStream; 024import java.io.Serializable; 025import java.lang.reflect.Array; 026import java.lang.reflect.InvocationHandler; 027import java.lang.reflect.Method; 028import java.lang.reflect.Proxy; 029import java.util.ArrayList; 030import java.util.List; 031import java.util.concurrent.CopyOnWriteArrayList; 032 033import org.apache.commons.lang3.Validate; 034 035/** 036 * <p>An EventListenerSupport object can be used to manage a list of event 037 * listeners of a particular type. The class provides 038 * {@link #addListener(Object)} and {@link #removeListener(Object)} methods 039 * for registering listeners, as well as a {@link #fire()} method for firing 040 * events to the listeners. 041 * </p> 042 * 043 * <p> 044 * To use this class, suppose you want to support ActionEvents. You would do: 045 * </p> 046 * <pre><code> 047 * public class MyActionEventSource 048 * { 049 * private EventListenerSupport<ActionListener> actionListeners = 050 * EventListenerSupport.create(ActionListener.class); 051 * 052 * public void someMethodThatFiresAction() 053 * { 054 * ActionEvent e = new ActionEvent(this, ActionEvent.ACTION_PERFORMED, "somethingCool"); 055 * actionListeners.fire().actionPerformed(e); 056 * } 057 * } 058 * </code></pre> 059 * 060 * <p> 061 * Serializing an {@link EventListenerSupport} instance will result in any 062 * non-{@link Serializable} listeners being silently dropped. 063 * </p> 064 * 065 * @param <L> the type of event listener that is supported by this proxy. 066 * 067 * @since 3.0 068 */ 069public class EventListenerSupport<L> implements Serializable { 070 071 /** Serialization version */ 072 private static final long serialVersionUID = 3593265990380473632L; 073 074 /** 075 * The list used to hold the registered listeners. This list is 076 * intentionally a thread-safe copy-on-write-array so that traversals over 077 * the list of listeners will be atomic. 078 */ 079 private List<L> listeners = new CopyOnWriteArrayList<>(); 080 081 /** 082 * The proxy representing the collection of listeners. Calls to this proxy 083 * object will sent to all registered listeners. 084 */ 085 private transient L proxy; 086 087 /** 088 * Empty typed array for #getListeners(). 089 */ 090 private transient L[] prototypeArray; 091 092 /** 093 * Creates an EventListenerSupport object which supports the specified 094 * listener type. 095 * 096 * @param <T> the type of the listener interface 097 * @param listenerInterface the type of listener interface that will receive 098 * events posted using this class. 099 * 100 * @return an EventListenerSupport object which supports the specified 101 * listener type. 102 * 103 * @throws NullPointerException if {@code listenerInterface} is 104 * {@code null}. 105 * @throws IllegalArgumentException if {@code listenerInterface} is 106 * not an interface. 107 */ 108 public static <T> EventListenerSupport<T> create(final Class<T> listenerInterface) { 109 return new EventListenerSupport<>(listenerInterface); 110 } 111 112 /** 113 * Creates an EventListenerSupport object which supports the provided 114 * listener interface. 115 * 116 * @param listenerInterface the type of listener interface that will receive 117 * events posted using this class. 118 * 119 * @throws NullPointerException if {@code listenerInterface} is 120 * {@code null}. 121 * @throws IllegalArgumentException if {@code listenerInterface} is 122 * not an interface. 123 */ 124 public EventListenerSupport(final Class<L> listenerInterface) { 125 this(listenerInterface, Thread.currentThread().getContextClassLoader()); 126 } 127 128 /** 129 * Creates an EventListenerSupport object which supports the provided 130 * listener interface using the specified class loader to create the JDK 131 * dynamic proxy. 132 * 133 * @param listenerInterface the listener interface. 134 * @param classLoader the class loader. 135 * 136 * @throws NullPointerException if {@code listenerInterface} or 137 * {@code classLoader} is {@code null}. 138 * @throws IllegalArgumentException if {@code listenerInterface} is 139 * not an interface. 140 */ 141 public EventListenerSupport(final Class<L> listenerInterface, final ClassLoader classLoader) { 142 this(); 143 Validate.notNull(listenerInterface, "Listener interface cannot be null."); 144 Validate.notNull(classLoader, "ClassLoader cannot be null."); 145 Validate.isTrue(listenerInterface.isInterface(), "Class %s is not an interface", 146 listenerInterface.getName()); 147 initializeTransientFields(listenerInterface, classLoader); 148 } 149 150 /** 151 * Create a new EventListenerSupport instance. 152 * Serialization-friendly constructor. 153 */ 154 private EventListenerSupport() { 155 } 156 157 /** 158 * Returns a proxy object which can be used to call listener methods on all 159 * of the registered event listeners. All calls made to this proxy will be 160 * forwarded to all registered listeners. 161 * 162 * @return a proxy object which can be used to call listener methods on all 163 * of the registered event listeners 164 */ 165 public L fire() { 166 return proxy; 167 } 168 169//********************************************************************************************************************** 170// Other Methods 171//********************************************************************************************************************** 172 173 /** 174 * Registers an event listener. 175 * 176 * @param listener the event listener (may not be {@code null}). 177 * 178 * @throws NullPointerException if {@code listener} is 179 * {@code null}. 180 */ 181 public void addListener(final L listener) { 182 addListener(listener, true); 183 } 184 185 /** 186 * Registers an event listener. Will not add a pre-existing listener 187 * object to the list if {@code allowDuplicate} is false. 188 * 189 * @param listener the event listener (may not be {@code null}). 190 * @param allowDuplicate the flag for determining if duplicate listener 191 * objects are allowed to be registered. 192 * 193 * @throws NullPointerException if {@code listener} is {@code null}. 194 * @since 3.5 195 */ 196 public void addListener(final L listener, final boolean allowDuplicate) { 197 Validate.notNull(listener, "Listener object cannot be null."); 198 if (allowDuplicate || !listeners.contains(listener)) { 199 listeners.add(listener); 200 } 201 } 202 203 /** 204 * Returns the number of registered listeners. 205 * 206 * @return the number of registered listeners. 207 */ 208 int getListenerCount() { 209 return listeners.size(); 210 } 211 212 /** 213 * Unregisters an event listener. 214 * 215 * @param listener the event listener (may not be {@code null}). 216 * 217 * @throws NullPointerException if {@code listener} is 218 * {@code null}. 219 */ 220 public void removeListener(final L listener) { 221 Validate.notNull(listener, "Listener object cannot be null."); 222 listeners.remove(listener); 223 } 224 225 /** 226 * Gets an array containing the currently registered listeners. 227 * Modification to this array's elements will have no effect on the 228 * {@link EventListenerSupport} instance. 229 * @return L[] 230 */ 231 public L[] getListeners() { 232 return listeners.toArray(prototypeArray); 233 } 234 235 /** 236 * Serialize. 237 * @param objectOutputStream the output stream 238 * @throws IOException if an IO error occurs 239 */ 240 private void writeObject(final ObjectOutputStream objectOutputStream) throws IOException { 241 final ArrayList<L> serializableListeners = new ArrayList<>(); 242 243 // don't just rely on instanceof Serializable: 244 ObjectOutputStream testObjectOutputStream = new ObjectOutputStream(new ByteArrayOutputStream()); 245 for (final L listener : listeners) { 246 try { 247 testObjectOutputStream.writeObject(listener); 248 serializableListeners.add(listener); 249 } catch (final IOException exception) { 250 //recreate test stream in case of indeterminate state 251 testObjectOutputStream = new ObjectOutputStream(new ByteArrayOutputStream()); 252 } 253 } 254 /* 255 * we can reconstitute everything we need from an array of our listeners, 256 * which has the additional advantage of typically requiring less storage than a list: 257 */ 258 objectOutputStream.writeObject(serializableListeners.toArray(prototypeArray)); 259 } 260 261 /** 262 * Deserialize. 263 * @param objectInputStream the input stream 264 * @throws IOException if an IO error occurs 265 * @throws ClassNotFoundException if the class cannot be resolved 266 */ 267 private void readObject(final ObjectInputStream objectInputStream) throws IOException, ClassNotFoundException { 268 @SuppressWarnings("unchecked") // Will throw CCE here if not correct 269 final 270 L[] srcListeners = (L[]) objectInputStream.readObject(); 271 272 this.listeners = new CopyOnWriteArrayList<>(srcListeners); 273 274 @SuppressWarnings("unchecked") // Will throw CCE here if not correct 275 final 276 Class<L> listenerInterface = (Class<L>) srcListeners.getClass().getComponentType(); 277 278 initializeTransientFields(listenerInterface, Thread.currentThread().getContextClassLoader()); 279 } 280 281 /** 282 * Initialize transient fields. 283 * @param listenerInterface the class of the listener interface 284 * @param classLoader the class loader to be used 285 */ 286 private void initializeTransientFields(final Class<L> listenerInterface, final ClassLoader classLoader) { 287 @SuppressWarnings("unchecked") // Will throw CCE here if not correct 288 final 289 L[] array = (L[]) Array.newInstance(listenerInterface, 0); 290 this.prototypeArray = array; 291 createProxy(listenerInterface, classLoader); 292 } 293 294 /** 295 * Create the proxy object. 296 * @param listenerInterface the class of the listener interface 297 * @param classLoader the class loader to be used 298 */ 299 private void createProxy(final Class<L> listenerInterface, final ClassLoader classLoader) { 300 proxy = listenerInterface.cast(Proxy.newProxyInstance(classLoader, 301 new Class[] { listenerInterface }, createInvocationHandler())); 302 } 303 304 /** 305 * Create the {@link InvocationHandler} responsible for broadcasting calls 306 * to the managed listeners. Subclasses can override to provide custom behavior. 307 * @return ProxyInvocationHandler 308 */ 309 protected InvocationHandler createInvocationHandler() { 310 return new ProxyInvocationHandler(); 311 } 312 313 /** 314 * An invocation handler used to dispatch the event(s) to all the listeners. 315 */ 316 protected class ProxyInvocationHandler implements InvocationHandler { 317 318 /** 319 * Propagates the method call to all registered listeners in place of 320 * the proxy listener object. 321 * 322 * @param unusedProxy the proxy object representing a listener on which the 323 * invocation was called; not used 324 * @param method the listener method that will be called on all of the 325 * listeners. 326 * @param args event arguments to propagate to the listeners. 327 * @return the result of the method call 328 * @throws Throwable if an error occurs 329 */ 330 @Override 331 public Object invoke(final Object unusedProxy, final Method method, final Object[] args) throws Throwable { 332 for (final L listener : listeners) { 333 method.invoke(listener, args); 334 } 335 return null; 336 } 337 } 338}