1 /* 2 * Copyright (C) 2012 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 5 * in compliance with the License. You may obtain a copy of the License at 6 * 7 * http://www.apache.org/licenses/LICENSE-2.0 8 * 9 * Unless required by applicable law or agreed to in writing, software distributed under the License 10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 11 * or implied. See the License for the specific language governing permissions and limitations under 12 * the License. 13 */ 14 15 package com.google.common.reflect; 16 17 import java.lang.reflect.InvocationHandler; 18 import java.lang.reflect.Method; 19 import java.lang.reflect.Proxy; 20 import java.util.Arrays; 21 import javax.annotation.CheckForNull; 22 import org.checkerframework.checker.nullness.qual.Nullable; 23 24 /** 25 * Abstract implementation of {@link InvocationHandler} that handles {@link Object#equals}, {@link 26 * Object#hashCode} and {@link Object#toString}. For example: 27 * 28 * <pre> 29 * class Unsupported extends AbstractInvocationHandler { 30 * protected Object handleInvocation(Object proxy, Method method, Object[] args) { 31 * throw new UnsupportedOperationException(); 32 * } 33 * } 34 * 35 * CharSequence unsupported = Reflection.newProxy(CharSequence.class, new Unsupported()); 36 * </pre> 37 * 38 * @author Ben Yu 39 * @since 12.0 40 */ 41 @ElementTypesAreNonnullByDefault 42 public abstract class AbstractInvocationHandler implements InvocationHandler { 43 44 private static final Object[] NO_ARGS = {}; 45 46 /** 47 * {@inheritDoc} 48 * 49 * <ul> 50 * <li>{@code proxy.hashCode()} delegates to {@link AbstractInvocationHandler#hashCode} 51 * <li>{@code proxy.toString()} delegates to {@link AbstractInvocationHandler#toString} 52 * <li>{@code proxy.equals(argument)} returns true if: 53 * <ul> 54 * <li>{@code proxy} and {@code argument} are of the same type 55 * <li>and {@link AbstractInvocationHandler#equals} returns true for the {@link 56 * InvocationHandler} of {@code argument} 57 * </ul> 58 * <li>other method calls are dispatched to {@link #handleInvocation}. 59 * </ul> 60 */ 61 @Override 62 @CheckForNull invoke(Object proxy, Method method, @CheckForNull @Nullable Object[] args)63 public final Object invoke(Object proxy, Method method, @CheckForNull @Nullable Object[] args) 64 throws Throwable { 65 if (args == null) { 66 args = NO_ARGS; 67 } 68 if (args.length == 0 && method.getName().equals("hashCode")) { 69 return hashCode(); 70 } 71 if (args.length == 1 72 && method.getName().equals("equals") 73 && method.getParameterTypes()[0] == Object.class) { 74 Object arg = args[0]; 75 if (arg == null) { 76 return false; 77 } 78 if (proxy == arg) { 79 return true; 80 } 81 return isProxyOfSameInterfaces(arg, proxy.getClass()) 82 && equals(Proxy.getInvocationHandler(arg)); 83 } 84 if (args.length == 0 && method.getName().equals("toString")) { 85 return toString(); 86 } 87 return handleInvocation(proxy, method, args); 88 } 89 90 /** 91 * {@link #invoke} delegates to this method upon any method invocation on the proxy instance, 92 * except {@link Object#equals}, {@link Object#hashCode} and {@link Object#toString}. The result 93 * will be returned as the proxied method's return value. 94 * 95 * <p>Unlike {@link #invoke}, {@code args} will never be null. When the method has no parameter, 96 * an empty array is passed in. 97 */ 98 @CheckForNull handleInvocation(Object proxy, Method method, @Nullable Object[] args)99 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 equals(@heckForNull Object obj)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 hashCode()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 toString()133 public String toString() { 134 return super.toString(); 135 } 136 isProxyOfSameInterfaces(Object arg, Class<?> proxyClass)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 } 148