    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 *      https://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.InvocationHandler;
    026import java.lang.reflect.InvocationTargetException;
    027import java.lang.reflect.Method;
    028import java.lang.reflect.Proxy;
    029import java.util.ArrayList;
    030import java.util.List;
    031import java.util.Objects;
    032import java.util.concurrent.CopyOnWriteArrayList;
    033
    034import org.apache.commons.lang3.ArrayUtils;
    035import org.apache.commons.lang3.Validate;
    036import org.apache.commons.lang3.exception.ExceptionUtils;
    037import org.apache.commons.lang3.function.FailableConsumer;
    038
    039/**
    040 * Manages a list of event listeners of a given generic type. This class provides {@link #addListener(Object)} and {@link #removeListener(Object)} methods for
    041 * managing listeners, as well as a {@link #fire()} method for firing events to the listeners.
    042 *
    043 * <p>
    044 * For example, to support ActionEvents:
    045 * </p>
    046 *
    047 * <pre>{@code
    048 * public class MyActionEventSource {
    049 *
    050 *     private EventListenerSupport<ActionListener> actionListeners = EventListenerSupport.create(ActionListener.class);
    051 *
    052 *     public void someMethodThatFiresAction() {
    053 *         ActionEvent e = new ActionEvent(this, ActionEvent.ACTION_PERFORMED, "something");
    054 *         actionListeners.fire().actionPerformed(e);
    055 *     }
    056 * }
    057 * }</pre>
    058 * <p>
    059 * Events are fired
    060 * <p>
    061 * Serializing an {@link EventListenerSupport} instance will result in any non-{@link Serializable} listeners being silently dropped.
    062 * </p>
    063 *
    064 * @param <L> the type of event listener that is supported by this proxy.
    065 * @since 3.0
    066 */
    067public class EventListenerSupport<L> implements Serializable {
    068
    069    /**
    070     * Invokes listeners through {@link #invoke(Object, Method, Object[])} in the order added to the underlying {@link List}.
    071     */
    072    protected class ProxyInvocationHandler implements InvocationHandler {
    073
    074        private final FailableConsumer<Throwable, IllegalAccessException> handler;
    075
    076        /**
    077         * Constructs a new instance.
    078         */
    079        public ProxyInvocationHandler() {
    080            this(ExceptionUtils::rethrow);
    081        }
    082
    083        /**
    084         * Constructs a new instance.
    085         *
    086         * @param handler Handles Throwables.
    087         * @since 3.15.0
    088         */
    089        public ProxyInvocationHandler(final FailableConsumer<Throwable, IllegalAccessException> handler) {
    090            this.handler = Objects.requireNonNull(handler);
    091        }
    092
    093        /**
    094         * Handles an exception thrown by a listener. By default rethrows the given Throwable.
    095         *
    096         * @param t The Throwable
    097         * @throws IllegalAccessException thrown by the listener.
    098         * @throws IllegalArgumentException thrown by the listener.
    099         * @throws InvocationTargetException thrown by the listener.
    100         * @since 3.15.0
    101         */
    102        protected void handle(final Throwable t) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException {
    103            handler.accept(t);
    104        }
    105
    106        /**
    107         * Propagates the method call to all registered listeners in place of the proxy listener object.
    108         * <p>
    109         * Calls listeners in the order added to the underlying {@link List}.
    110         * </p>
    111         *
    112         * @param unusedProxy the proxy object representing a listener on which the invocation was called; not used
    113         * @param method the listener method that will be called on all of the listeners.
    114         * @param args event arguments to propagate to the listeners.
    115         * @return the result of the method call
    116         * @throws InvocationTargetException if an error occurs
    117         * @throws IllegalArgumentException if an error occurs
    118         * @throws IllegalAccessException if an error occurs
    119         */
    120        @Override
    121        public Object invoke(final Object unusedProxy, final Method method, final Object[] args)
    122                throws IllegalAccessException, IllegalArgumentException, InvocationTargetException {
    123            for (final L listener : listeners) {
    124                try {
    125                    method.invoke(listener, args);
    126                } catch (final Throwable t) {
    127                    handle(t);
    128                }
    129            }
    130            return null;
    131        }
    132    }
    133
    134    /** Serialization version */
    135    private static final long serialVersionUID = 3593265990380473632L;
    136
    137    /**
    138     * Creates an EventListenerSupport object which supports the specified
    139     * listener type.
    140     *
    141     * @param <T> the type of the listener interface
    142     * @param listenerInterface the type of listener interface that will receive
    143     *        events posted using this class.
    144     *
    145     * @return an EventListenerSupport object which supports the specified
    146     *         listener type.
    147     *
    148     * @throws NullPointerException if {@code listenerInterface} is
    149     *         {@code null}.
    150     * @throws IllegalArgumentException if {@code listenerInterface} is
    151     *         not an interface.
    152     */
    153    public static <T> EventListenerSupport<T> create(final Class<T> listenerInterface) {
    154        return new EventListenerSupport<>(listenerInterface);
    155    }
    156
    157    /**
    158     * Hold the registered listeners. This list is intentionally a thread-safe copy-on-write-array so that traversals over the list of listeners will be atomic.
    159     */
    160    private List<L> listeners = new CopyOnWriteArrayList<>();
    161
    162    /**
    163     * The proxy representing the collection of listeners. Calls to this proxy object will be sent to all registered listeners.
    164     */
    165    private transient L proxy;
    166    /**
    167     * Empty typed array for #getListeners().
    168     */
    169    private transient L[] prototypeArray;
    170
    171    /**
    172     * Constructs a new EventListenerSupport instance.
    173     * <p>
    174     * This constructor is needed for serialization.
    175     * </p>
    176     */
    177    private EventListenerSupport() {
    178    }
    179
    180    /**
    181     * Constructs an EventListenerSupport object which supports the provided
    182     * listener interface.
    183     *
    184     * @param listenerInterface the type of listener interface that will receive
    185     *        events posted using this class.
    186     *
    187     * @throws NullPointerException if {@code listenerInterface} is
    188     *         {@code null}.
    189     * @throws IllegalArgumentException if {@code listenerInterface} is
    190     *         not an interface.
    191     */
    192    public EventListenerSupport(final Class<L> listenerInterface) {
    193        this(listenerInterface, Thread.currentThread().getContextClassLoader());
    194    }
    195
    196    /**
    197     * Constructs an EventListenerSupport object which supports the provided
    198     * listener interface using the specified class loader to create the JDK
    199     * dynamic proxy.
    200     *
    201     * @param listenerInterface the listener interface.
    202     * @param classLoader       the class loader.
    203     * @throws NullPointerException if {@code listenerInterface} or
    204     *         {@code classLoader} is {@code null}.
    205     * @throws IllegalArgumentException if {@code listenerInterface} is
    206     *         not an interface.
    207     */
    208    public EventListenerSupport(final Class<L> listenerInterface, final ClassLoader classLoader) {
    209        this();
    210        Objects.requireNonNull(listenerInterface, "listenerInterface");
    211        Objects.requireNonNull(classLoader, "classLoader");
    212        Validate.isTrue(listenerInterface.isInterface(), "Class %s is not an interface", listenerInterface.getName());
    213        initializeTransientFields(listenerInterface, classLoader);
    214    }
    215
    216    /**
    217     * Adds an event listener.
    218     * <p>
    219     * Listeners are called in the order added.
    220     * </p>
    221     *
    222     * @param listener the event listener (may not be {@code null}).
    223     * @throws NullPointerException if {@code listener} is {@code null}.
    224     */
    225    public void addListener(final L listener) {
    226        addListener(listener, true);
    227    }
    228
    229    /**
    230     * Adds an event listener. Will not add a pre-existing listener object to the list if {@code allowDuplicate} is false.
    231     * <p>
    232     * Listeners are called in the order added.
    233     * </p>
    234     *
    235     * @param listener       the event listener (may not be {@code null}).
    236     * @param allowDuplicate the flag for determining if duplicate listener objects are allowed to be registered.
    237     *
    238     * @throws NullPointerException if {@code listener} is {@code null}.
    239     * @since 3.5
    240     */
    241    public void addListener(final L listener, final boolean allowDuplicate) {
    242        Objects.requireNonNull(listener, "listener");
    243        if (allowDuplicate || !listeners.contains(listener)) {
    244            listeners.add(listener);
    245        }
    246    }
    247
    248    /**
    249     * Creates the {@link InvocationHandler} responsible for calling
    250     * to the managed listeners. Subclasses can override to provide custom behavior.
    251     *
    252     * @return ProxyInvocationHandler
    253     */
    254    protected InvocationHandler createInvocationHandler() {
    255        return new ProxyInvocationHandler();
    256    }
    257
    258    /**
    259     * Creates the proxy object.
    260     *
    261     * @param listenerInterface the class of the listener interface
    262     * @param classLoader the class loader to be used
    263     */
    264    private void createProxy(final Class<L> listenerInterface, final ClassLoader classLoader) {
    265        proxy = listenerInterface.cast(Proxy.newProxyInstance(classLoader, new Class[] { listenerInterface }, createInvocationHandler()));
    266    }
    267
    268    /**
    269     * Returns a proxy object which can be used to call listener methods on all
    270     * of the registered event listeners. All calls made to this proxy will be
    271     * forwarded to all registered listeners.
    272     *
    273     * @return a proxy object which can be used to call listener methods on all
    274     * of the registered event listeners
    275     */
    276    public L fire() {
    277        return proxy;
    278    }
    279
    280    /**
    281     * Gets the number of registered listeners.
    282     *
    283     * @return the number of registered listeners.
    284     */
    285    int getListenerCount() {
    286        return listeners.size();
    287    }
    288
    289    /**
    290     * Gets an array containing the currently registered listeners.
    291     * Modification to this array's elements will have no effect on the
    292     * {@link EventListenerSupport} instance.
    293     * @return L[]
    294     */
    295    public L[] getListeners() {
    296        return listeners.toArray(prototypeArray);
    297    }
    298
    299    /**
    300     * Initializes transient fields.
    301     *
    302     * @param listenerInterface the class of the listener interface
    303     * @param classLoader the class loader to be used
    304     */
    305    private void initializeTransientFields(final Class<L> listenerInterface, final ClassLoader classLoader) {
    306        // Will throw CCE here if not correct
    307        this.prototypeArray = ArrayUtils.newInstance(listenerInterface, 0);
    308        createProxy(listenerInterface, classLoader);
    309    }
    310
    311    /**
    312     * Deserializes the next object into this instance.
    313     *
    314     * @param objectInputStream the input stream
    315     * @throws IOException if an IO error occurs
    316     * @throws ClassNotFoundException if the class cannot be resolved
    317     */
    318    private void readObject(final ObjectInputStream objectInputStream) throws IOException, ClassNotFoundException {
    319        @SuppressWarnings("unchecked") // Will throw CCE here if not correct
    320        final L[] srcListeners = (L[]) objectInputStream.readObject();
    321        this.listeners = new CopyOnWriteArrayList<>(srcListeners);
    322        final Class<L> listenerInterface = ArrayUtils.getComponentType(srcListeners);
    323        initializeTransientFields(listenerInterface, Thread.currentThread().getContextClassLoader());
    324    }
    325
    326    /**
    327     * Removes an event listener.
    328     *
    329     * @param listener the event listener (may not be {@code null}).
    330     * @throws NullPointerException if {@code listener} is
    331     *         {@code null}.
    332     */
    333    public void removeListener(final L listener) {
    334        listeners.remove(Objects.requireNonNull(listener, "listener"));
    335    }
    336
    337    /**
    338     * Serializes this instance onto the given ObjectOutputStream.
    339     *
    340     * @param objectOutputStream the output stream
    341     * @throws IOException if an IO error occurs
    342     */
    343    private void writeObject(final ObjectOutputStream objectOutputStream) throws IOException {
    344        final ArrayList<L> serializableListeners = new ArrayList<>();
    345        // Don't just rely on instanceof Serializable:
    346        ObjectOutputStream testObjectOutputStream = new ObjectOutputStream(new ByteArrayOutputStream());
    347        for (final L listener : listeners) {
    348            try {
    349                testObjectOutputStream.writeObject(listener);
    350                serializableListeners.add(listener);
    351            } catch (final IOException exception) {
    352                //recreate test stream in case of indeterminate state
    353                testObjectOutputStream = new ObjectOutputStream(new ByteArrayOutputStream());
    354            }
    355        }
    356        // We can reconstitute everything we need from an array of our listeners,
    357        // which has the additional advantage of typically requiring less storage than a list:
    358        objectOutputStream.writeObject(serializableListeners.toArray(prototypeArray));
    359    }
    360}