001/* 002 * Copyright (C) 2012 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 005 * in compliance with the License. You may obtain a copy of the License at 006 * 007 * http://www.apache.org/licenses/LICENSE-2.0 008 * 009 * Unless required by applicable law or agreed to in writing, software distributed under the License 010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 011 * or implied. See the License for the specific language governing permissions and limitations under 012 * the License. 013 */ 014 015package com.google.common.reflect; 016 017import java.lang.reflect.InvocationHandler; 018import java.lang.reflect.Method; 019import java.lang.reflect.Proxy; 020import java.util.Arrays; 021import javax.annotation.CheckForNull; 022import org.checkerframework.checker.nullness.qual.Nullable; 023 024/** 025 * Abstract implementation of {@link InvocationHandler} that handles {@link Object#equals}, {@link 026 * Object#hashCode} and {@link Object#toString}. For example: 027 * 028 * <pre> 029 * class Unsupported extends AbstractInvocationHandler { 030 * protected Object handleInvocation(Object proxy, Method method, Object[] args) { 031 * throw new UnsupportedOperationException(); 032 * } 033 * } 034 * 035 * CharSequence unsupported = Reflection.newProxy(CharSequence.class, new Unsupported()); 036 * </pre> 037 * 038 * @author Ben Yu 039 * @since 12.0 040 */ 041@ElementTypesAreNonnullByDefault 042public abstract class AbstractInvocationHandler implements InvocationHandler { 043 044 private static final Object[] NO_ARGS = {}; 045 046 /** 047 * {@inheritDoc} 048 * 049 * <ul> 050 * <li>{@code proxy.hashCode()} delegates to {@link AbstractInvocationHandler#hashCode} 051 * <li>{@code proxy.toString()} delegates to {@link AbstractInvocationHandler#toString} 052 * <li>{@code proxy.equals(argument)} returns true if: 053 * <ul> 054 * <li>{@code proxy} and {@code argument} are of the same type 055 * <li>and {@link AbstractInvocationHandler#equals} returns true for the {@link 056 * InvocationHandler} of {@code argument} 057 * </ul> 058 * <li>other method calls are dispatched to {@link #handleInvocation}. 059 * </ul> 060 */ 061 @Override 062 @CheckForNull 063 public final Object invoke(Object proxy, Method method, @CheckForNull @Nullable Object[] args) 064 throws Throwable { 065 if (args == null) { 066 args = NO_ARGS; 067 } 068 if (args.length == 0 && method.getName().equals("hashCode")) { 069 return hashCode(); 070 } 071 if (args.length == 1 072 && method.getName().equals("equals") 073 && method.getParameterTypes()[0] == Object.class) { 074 Object arg = args[0]; 075 if (arg == null) { 076 return false; 077 } 078 if (proxy == arg) { 079 return true; 080 } 081 return isProxyOfSameInterfaces(arg, proxy.getClass()) 082 && equals(Proxy.getInvocationHandler(arg)); 083 } 084 if (args.length == 0 && method.getName().equals("toString")) { 085 return toString(); 086 } 087 return handleInvocation(proxy, method, args); 088 } 089 090 /** 091 * {@link #invoke} delegates to this method upon any method invocation on the proxy instance, 092 * except {@link Object#equals}, {@link Object#hashCode} and {@link Object#toString}. The result 093 * will be returned as the proxied method's return value. 094 * 095 * <p>Unlike {@link #invoke}, {@code args} will never be null. When the method has no parameter, 096 * an empty array is passed in. 097 */ 098 @CheckForNull 099 protected abstract Object handleInvocation(Object proxy, Method method, @Nullable Object[] args) 100 throws Throwable; 101 102 /** 103 * By default delegates to {@link Object#equals} so instances are only equal if they are 104 * identical. {@code proxy.equals(argument)} returns true if: 105 * 106 * <ul> 107 * <li>{@code proxy} and {@code argument} are of the same type 108 * <li>and this method returns true for the {@link InvocationHandler} of {@code argument} 109 * </ul> 110 * 111 * <p>Subclasses can override this method to provide custom equality. 112 */ 113 @Override 114 public boolean equals(@CheckForNull Object obj) { 115 return super.equals(obj); 116 } 117 118 /** 119 * By default delegates to {@link Object#hashCode}. The dynamic proxies' {@code hashCode()} will 120 * delegate to this method. Subclasses can override this method to provide custom equality. 121 */ 122 @Override 123 public int hashCode() { 124 return super.hashCode(); 125 } 126 127 /** 128 * By default delegates to {@link Object#toString}. The dynamic proxies' {@code toString()} will 129 * delegate to this method. Subclasses can override this method to provide custom string 130 * representation for the proxies. 131 */ 132 @Override 133 public String toString() { 134 return super.toString(); 135 } 136 137 private static boolean isProxyOfSameInterfaces(Object arg, Class<?> proxyClass) { 138 return proxyClass.isInstance(arg) 139 // Equal proxy instances should mostly be instance of proxyClass 140 // Under some edge cases (such as the proxy of JDK types serialized and then deserialized) 141 // the proxy type may not be the same. 142 // We first check isProxyClass() so that the common case of comparing with non-proxy objects 143 // is efficient. 144 || (Proxy.isProxyClass(arg.getClass()) 145 && Arrays.equals(arg.getClass().getInterfaces(), proxyClass.getInterfaces())); 146 } 147}