/* * Copyright (C) 2012 The Guava Authors * * Licensed 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 com.google.common.reflect; import com.google.common.annotations.Beta; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import java.util.Arrays; import javax.annotation.Nullable; /** * Abstract implementation of {@link InvocationHandler} that handles {@link Object#equals}, * {@link Object#hashCode} and {@link Object#toString}. For example:
 * class Unsupported extends AbstractInvocationHandler {
 *   protected Object handleInvocation(
 *       Object proxy, Method method, Object[] args) {
 *     throw new UnsupportedOperationException();
 *   }
 * }
 *
 * CharSequence unsupported = Reflection.newProxy(CharSequence.class, new Unsupported());
 * 
* * @author Ben Yu * @since 12.0 */ @Beta public abstract class AbstractInvocationHandler implements InvocationHandler { private static final Object[] NO_ARGS = {}; /** * {@inheritDoc} * *

*/ @Override public final Object invoke(Object proxy, Method method, @Nullable Object[] args) throws Throwable { if (args == null) { args = NO_ARGS; } if (args.length == 0 && method.getName().equals("hashCode")) { return hashCode(); } if (args.length == 1 && method.getName().equals("equals") && method.getParameterTypes()[0] == Object.class) { Object arg = args[0]; if (arg == null) { return false; } if (proxy == arg) { return true; } return isProxyOfSameInterfaces(arg, proxy.getClass()) && equals(Proxy.getInvocationHandler(arg)); } if (args.length == 0 && method.getName().equals("toString")) { return toString(); } return handleInvocation(proxy, method, args); } /** * {@link #invoke} delegates to this method upon any method invocation on the proxy instance, * except {@link Object#equals}, {@link Object#hashCode} and {@link Object#toString}. The result * will be returned as the proxied method's return value. * *

Unlike {@link #invoke}, {@code args} will never be null. When the method has no parameter, * an empty array is passed in. */ protected abstract Object handleInvocation(Object proxy, Method method, Object[] args) throws Throwable; /** * By default delegates to {@link Object#equals} so instances are only equal if they are * identical. {@code proxy.equals(argument)} returns true if:

*

Subclasses can override this method to provide custom equality. */ @Override public boolean equals(Object obj) { return super.equals(obj); } /** * By default delegates to {@link Object#hashCode}. The dynamic proxies' {@code hashCode()} will * delegate to this method. Subclasses can override this method to provide custom equality. */ @Override public int hashCode() { return super.hashCode(); } /** * By default delegates to {@link Object#toString}. The dynamic proxies' {@code toString()} will * delegate to this method. Subclasses can override this method to provide custom string * representation for the proxies. */ @Override public String toString() { return super.toString(); } private static boolean isProxyOfSameInterfaces(Object arg, Class proxyClass) { return proxyClass.isInstance(arg) // Equal proxy instances should mostly be instance of proxyClass // Under some edge cases (such as the proxy of JDK types serialized and then deserialized) // the proxy type may not be the same. // We first check isProxyClass() so that the common case of comparing with non-proxy objects // is efficient. || (Proxy.isProxyClass(arg.getClass()) && Arrays.equals(arg.getClass().getInterfaces(), proxyClass.getInterfaces())); } }