1 /* 2 * Copyright (C) 2012 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.reflect; 18 19 import com.google.common.annotations.Beta; 20 21 import java.lang.reflect.InvocationHandler; 22 import java.lang.reflect.Method; 23 import java.lang.reflect.Proxy; 24 import java.util.Arrays; 25 26 import javax.annotation.Nullable; 27 28 /** 29 * Abstract implementation of {@link InvocationHandler} that handles {@link Object#equals}, 30 * {@link Object#hashCode} and {@link Object#toString}. For example: <pre> 31 * class Unsupported extends AbstractInvocationHandler { 32 * protected Object handleInvocation( 33 * Object proxy, Method method, Object[] args) { 34 * throw new UnsupportedOperationException(); 35 * } 36 * } 37 * 38 * CharSequence unsupported = Reflection.newProxy(CharSequence.class, new Unsupported()); 39 * </pre> 40 * 41 * @author Ben Yu 42 * @since 12.0 43 */ 44 @Beta 45 public abstract class AbstractInvocationHandler implements InvocationHandler { 46 47 private static final Object[] NO_ARGS = {}; 48 49 /** 50 * {@inheritDoc} 51 * 52 * <p><ul> 53 * <li>{@code proxy.hashCode()} delegates to {@link AbstractInvocationHandler#hashCode} 54 * <li>{@code proxy.toString()} delegates to {@link AbstractInvocationHandler#toString} 55 * <li>{@code proxy.equals(argument)} returns true if: <ul> 56 * <li>{@code proxy} and {@code argument} are of the same type 57 * <li>and {@link AbstractInvocationHandler#equals} returns true for the {@link 58 * InvocationHandler} of {@code argument} 59 * </ul> 60 * <li>other method calls are dispatched to {@link #handleInvocation}. 61 * </ul> 62 */ invoke(Object proxy, Method method, @Nullable Object[] args)63 @Override public final Object invoke(Object proxy, Method method, @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 */ handleInvocation(Object proxy, Method method, Object[] args)98 protected abstract Object handleInvocation(Object proxy, Method method, Object[] args) 99 throws Throwable; 100 101 /** 102 * By default delegates to {@link Object#equals} so instances are only equal if they are 103 * identical. {@code proxy.equals(argument)} returns true if: <ul> 104 * <li>{@code proxy} and {@code argument} are of the same type 105 * <li>and this method returns true for the {@link InvocationHandler} of {@code argument} 106 * </ul> 107 * <p>Subclasses can override this method to provide custom equality. 108 */ equals(Object obj)109 @Override public boolean equals(Object obj) { 110 return super.equals(obj); 111 } 112 113 /** 114 * By default delegates to {@link Object#hashCode}. The dynamic proxies' {@code hashCode()} will 115 * delegate to this method. Subclasses can override this method to provide custom equality. 116 */ hashCode()117 @Override public int hashCode() { 118 return super.hashCode(); 119 } 120 121 /** 122 * By default delegates to {@link Object#toString}. The dynamic proxies' {@code toString()} will 123 * delegate to this method. Subclasses can override this method to provide custom string 124 * representation for the proxies. 125 */ toString()126 @Override public String toString() { 127 return super.toString(); 128 } 129 isProxyOfSameInterfaces(Object arg, Class<?> proxyClass)130 private static boolean isProxyOfSameInterfaces(Object arg, Class<?> proxyClass) { 131 return proxyClass.isInstance(arg) 132 // Equal proxy instances should mostly be instance of proxyClass 133 // Under some edge cases (such as the proxy of JDK types serialized and then deserialized) 134 // the proxy type may not be the same. 135 // We first check isProxyClass() so that the common case of comparing with non-proxy objects 136 // is efficient. 137 || (Proxy.isProxyClass(arg.getClass()) 138 && Arrays.equals(arg.getClass().getInterfaces(), proxyClass.getInterfaces())); 139 } 140 } 141