| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package org.apache.commons.proxy.invoker; |
| |
| import org.apache.commons.proxy.Invoker; |
| import org.apache.commons.proxy.ObjectProvider; |
| |
| import java.lang.reflect.Method; |
| |
| /** |
| * An invoker which supports <a href="http://en.wikipedia.org/wiki/Duck_typing">"duck typing"</a>, meaning |
| * that it finds a matching method on the object returned from the target provider and invokes it. This class is |
| * useful for adapting an existing class to an interface it does not implement. |
| * <p> |
| * <b>Example:</b> |
| * </p> |
| * <p> |
| * <pre> |
| * public class LegacyDuck // Does not implement interface! |
| * { |
| * public void quack() |
| * { |
| * // Quacking logic... |
| * } |
| * } |
| * <p/> |
| * public interface Duck |
| * { |
| * public void quack(); |
| * } |
| * <p/> |
| * ObjectProvider targetProvider = new ConstantProvider(new LegacyDuck()); // Always returns a "legacy" duck |
| * DuckTypingInvoker invoker = new DuckTypingInvoker(targetProvider); |
| * Duck duck = ( Duck )proxyFactory.createInvokerProxy( invoker, new Class[] { Duck.class } ); |
| * </pre> |
| * </p> |
| */ |
| public class DuckTypingInvoker implements Invoker |
| { |
| //********************************************************************************************************************** |
| // Fields |
| //********************************************************************************************************************** |
| |
| private final ObjectProvider targetProvider; |
| |
| //********************************************************************************************************************** |
| // Constructors |
| //********************************************************************************************************************** |
| |
| public DuckTypingInvoker( final ObjectProvider targetProvider ) |
| { |
| this.targetProvider = targetProvider; |
| } |
| |
| //********************************************************************************************************************** |
| // Invoker Implementation |
| //********************************************************************************************************************** |
| |
| public Object invoke( final Object proxy, final Method method, final Object[] arguments ) throws Throwable |
| { |
| final Object target = targetProvider.getObject(); |
| final Class targetClass = target.getClass(); |
| try |
| { |
| final Method targetMethod = targetClass.getMethod(method.getName(), method.getParameterTypes()); |
| if( method.getReturnType().isAssignableFrom(targetMethod.getReturnType()) ) |
| { |
| return targetMethod.invoke(target, arguments); |
| } |
| throw new UnsupportedOperationException( |
| "Target type " + targetClass.getName() + " method has incompatible return type."); |
| } |
| catch( NoSuchMethodException e ) |
| { |
| throw new UnsupportedOperationException( |
| "Target type " + targetClass.getName() + " does not have a method matching " + method + "."); |
| } |
| } |
| } |