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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.lang3.event;
19  
20  import java.lang.reflect.InvocationHandler;
21  import java.lang.reflect.InvocationTargetException;
22  import java.lang.reflect.Method;
23  import java.lang.reflect.Proxy;
24  import java.util.Arrays;
25  import java.util.HashSet;
26  import java.util.Set;
27  
28  import org.apache.commons.lang3.reflect.MethodUtils;
29  
30  /**
31   * Provides some useful event-based utility methods.
32   *
33   * @since 3.0
34   */
35  public class EventUtils {
36  
37      /**
38       * Adds an event listener to the specified source.  This looks for an "add" method corresponding to the event
39       * type (addActionListener, for example).
40       * @param eventSource   the event source
41       * @param listenerType  the event listener type
42       * @param listener      the listener
43       * @param <L>           the event listener type
44       *
45       * @throws IllegalArgumentException if the object doesn't support the listener type
46       */
47      public static <L> void addEventListener(final Object eventSource, final Class<L> listenerType, final L listener) {
48          try {
49              MethodUtils.invokeMethod(eventSource, "add" + listenerType.getSimpleName(), listener);
50          } catch (final NoSuchMethodException e) {
51              throw new IllegalArgumentException("Class " + eventSource.getClass().getName()
52                      + " does not have a public add" + listenerType.getSimpleName()
53                      + " method which takes a parameter of type " + listenerType.getName() + ".");
54          } catch (final IllegalAccessException e) {
55              throw new IllegalArgumentException("Class " + eventSource.getClass().getName()
56                      + " does not have an accessible add" + listenerType.getSimpleName ()
57                      + " method which takes a parameter of type " + listenerType.getName() + ".");
58          } catch (final InvocationTargetException e) {
59              throw new RuntimeException("Unable to add listener.", e.getCause());
60          }
61      }
62  
63      /**
64       * Binds an event listener to a specific method on a specific object.
65       *
66       * @param <L>          the event listener type
67       * @param target       the target object
68       * @param methodName   the name of the method to be called
69       * @param eventSource  the object which is generating events (JButton, JList, etc.)
70       * @param listenerType the listener interface (ActionListener.class, SelectionListener.class, etc.)
71       * @param eventTypes   the event types (method names) from the listener interface (if none specified, all will be
72       *                     supported)
73       */
74      public static <L> void bindEventsToMethod(final Object target, final String methodName, final Object eventSource,
75              final Class<L> listenerType, final String... eventTypes) {
76          final L listener = listenerType.cast(Proxy.newProxyInstance(target.getClass().getClassLoader(),
77                  new Class[] { listenerType }, new EventBindingInvocationHandler(target, methodName, eventTypes)));
78          addEventListener(eventSource, listenerType, listener);
79      }
80  
81      private static class EventBindingInvocationHandler implements InvocationHandler {
82          private final Object target;
83          private final String methodName;
84          private final Set<String> eventTypes;
85  
86          /**
87           * Creates a new instance of {@code EventBindingInvocationHandler}.
88           *
89           * @param target the target object for method invocations
90           * @param methodName the name of the method to be invoked
91           * @param eventTypes the names of the supported event types
92           */
93          EventBindingInvocationHandler(final Object target, final String methodName, final String[] eventTypes) {
94              this.target = target;
95              this.methodName = methodName;
96              this.eventTypes = new HashSet<String>(Arrays.asList(eventTypes));
97          }
98  
99          /**
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 }