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.proxy2.invoker;
019
020import java.lang.reflect.Method;
021
022import org.apache.commons.proxy2.Invoker;
023import org.apache.commons.proxy2.ObjectProvider;
024
025/**
026 * An invoker which supports <a href="http://en.wikipedia.org/wiki/Duck_typing">&quot;duck typing&quot;</a>, meaning
027 * that it finds a matching method on the object returned from the target provider and invokes it. This class is useful
028 * for adapting an existing class to an interface it does not implement.
029 * <p>
030 * <b>Example:</b>
031 * </p>
032 * <p>
033 * 
034 * <pre>
035 * public class LegacyDuck // Does not implement interface!
036 * {
037 *   public void quack()
038 *   {
039 *     // Quacking logic...
040 *   }
041 * }
042 * <p/>
043 * public interface Duck
044 * {
045 *   public void quack();
046 * }
047 * <p/>
048 * ObjectProvider targetProvider = new ConstantProvider(new LegacyDuck()); // Always returns a "legacy" duck
049 * DuckTypingInvoker invoker = new DuckTypingInvoker(targetProvider);
050 * Duck duck = ( Duck )proxyFactory.createInvokerProxy( invoker, new Class[] { Duck.class } );
051 * </pre>
052 * 
053 * </p>
054 */
055public class DuckTypingInvoker implements Invoker
056{
057    /** Serialization version */
058    private static final long serialVersionUID = 1L;
059
060    //******************************************************************************************************************
061    // Fields
062    //******************************************************************************************************************
063
064    private final ObjectProvider<?> targetProvider;
065
066    //******************************************************************************************************************
067    // Constructors
068    //******************************************************************************************************************
069
070    /**
071     * Create a new DuckTypingInvoker instance.
072     * 
073     * @param targetProvider
074     */
075    public DuckTypingInvoker(final ObjectProvider<?> targetProvider)
076    {
077        this.targetProvider = targetProvider;
078    }
079
080    //******************************************************************************************************************
081    // Invoker Implementation
082    //******************************************************************************************************************
083
084    /**
085     * {@inheritDoc}
086     */
087    @Override
088    public Object invoke(final Object proxy, final Method method, final Object[] arguments) throws Throwable
089    {
090        final Object target = targetProvider.getObject();
091        final Class<?> targetClass = target.getClass();
092        try
093        {
094            final Method targetMethod = targetClass.getMethod(method.getName(), method.getParameterTypes());
095            if (method.getReturnType().isAssignableFrom(targetMethod.getReturnType()))
096            {
097                return targetMethod.invoke(target, arguments);
098            }
099            throw new UnsupportedOperationException("Target type " + targetClass.getName()
100                    + " method has incompatible return type.");
101        }
102        catch (NoSuchMethodException e)
103        {
104            throw new UnsupportedOperationException("Target type " + targetClass.getName()
105                    + " does not have a method matching " + method + ".", e);
106        }
107    }
108}