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.lang.reflect.InvocationHandler;
021import java.lang.reflect.InvocationTargetException;
022import java.lang.reflect.Method;
023import java.lang.reflect.Proxy;
024import java.util.Arrays;
025import java.util.HashSet;
026import java.util.Set;
027
028import org.apache.commons.lang3.reflect.MethodUtils;
029
030/**
031 * Provides some useful event-based utility methods.
032 *
033 * @since 3.0
034 */
035public class EventUtils {
036
037    /**
038     * Adds an event listener to the specified source.  This looks for an "add" method corresponding to the event
039     * type (addActionListener, for example).
040     * @param eventSource   the event source
041     * @param listenerType  the event listener type
042     * @param listener      the listener
043     * @param <L>           the event listener type
044     *
045     * @throws IllegalArgumentException if the object doesn't support the listener type
046     */
047    public static <L> void addEventListener(final Object eventSource, final Class<L> listenerType, final L listener) {
048        try {
049            MethodUtils.invokeMethod(eventSource, "add" + listenerType.getSimpleName(), listener);
050        } catch (final NoSuchMethodException e) {
051            throw new IllegalArgumentException("Class " + eventSource.getClass().getName()
052                    + " does not have a public add" + listenerType.getSimpleName()
053                    + " method which takes a parameter of type " + listenerType.getName() + ".");
054        } catch (final IllegalAccessException e) {
055            throw new IllegalArgumentException("Class " + eventSource.getClass().getName()
056                    + " does not have an accessible add" + listenerType.getSimpleName ()
057                    + " method which takes a parameter of type " + listenerType.getName() + ".");
058        } catch (final InvocationTargetException e) {
059            throw new RuntimeException("Unable to add listener.", e.getCause());
060        }
061    }
062
063    /**
064     * Binds an event listener to a specific method on a specific object.
065     *
066     * @param <L>          the event listener type
067     * @param target       the target object
068     * @param methodName   the name of the method to be called
069     * @param eventSource  the object which is generating events (JButton, JList, etc.)
070     * @param listenerType the listener interface (ActionListener.class, SelectionListener.class, etc.)
071     * @param eventTypes   the event types (method names) from the listener interface (if none specified, all will be
072     *                     supported)
073     */
074    public static <L> void bindEventsToMethod(final Object target, final String methodName, final Object eventSource,
075            final Class<L> listenerType, final String... eventTypes) {
076        final L listener = listenerType.cast(Proxy.newProxyInstance(target.getClass().getClassLoader(),
077                new Class[] { listenerType }, new EventBindingInvocationHandler(target, methodName, eventTypes)));
078        addEventListener(eventSource, listenerType, listener);
079    }
080
081    private static class EventBindingInvocationHandler implements InvocationHandler {
082        private final Object target;
083        private final String methodName;
084        private final Set<String> eventTypes;
085
086        /**
087         * Creates a new instance of {@code EventBindingInvocationHandler}.
088         *
089         * @param target the target object for method invocations
090         * @param methodName the name of the method to be invoked
091         * @param eventTypes the names of the supported event types
092         */
093        EventBindingInvocationHandler(final Object target, final String methodName, final String[] eventTypes) {
094            this.target = target;
095            this.methodName = methodName;
096            this.eventTypes = new HashSet<>(Arrays.asList(eventTypes));
097        }
098
099        /**
100         * Handles a method invocation on the proxy object.
101         *
102         * @param proxy the proxy instance
103         * @param method the method to be invoked
104         * @param parameters the parameters for the method invocation
105         * @return the result of the method call
106         * @throws Throwable if an error occurs
107         */
108        @Override
109        public Object invoke(final Object proxy, final Method method, final Object[] parameters) throws Throwable {
110            if (eventTypes.isEmpty() || eventTypes.contains(method.getName())) {
111                if (hasMatchingParametersMethod(method)) {
112                    return MethodUtils.invokeMethod(target, methodName, parameters);
113                }
114                return MethodUtils.invokeMethod(target, methodName);
115            }
116            return null;
117        }
118
119        /**
120         * Checks whether a method for the passed in parameters can be found.
121         *
122         * @param method the listener method invoked
123         * @return a flag whether the parameters could be matched
124         */
125        private boolean hasMatchingParametersMethod(final Method method) {
126            return MethodUtils.getAccessibleMethod(target.getClass(), methodName, method.getParameterTypes()) != null;
127        }
128    }
129}