001/*
002 * Copyright 2002-2012 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.aop.framework;
018
019import org.springframework.core.NamedThreadLocal;
020
021/**
022 * Class containing static methods used to obtain information about the current AOP invocation.
023 *
024 * <p>The {@code currentProxy()} method is usable if the AOP framework is configured to
025 * expose the current proxy (not the default). It returns the AOP proxy in use. Target objects
026 * or advice can use this to make advised calls, in the same way as {@code getEJBObject()}
027 * can be used in EJBs. They can also use it to find advice configuration.
028 *
029 * <p>Spring's AOP framework does not expose proxies by default, as there is a performance cost
030 * in doing so.
031 *
032 * <p>The functionality in this class might be used by a target object that needed access
033 * to resources on the invocation. However, this approach should not be used when there is
034 * a reasonable alternative, as it makes application code dependent on usage under AOP and
035 * the Spring AOP framework in particular.
036 *
037 * @author Rod Johnson
038 * @author Juergen Hoeller
039 * @since 13.03.2003
040 */
041public abstract class AopContext {
042
043        /**
044         * ThreadLocal holder for AOP proxy associated with this thread.
045         * Will contain {@code null} unless the "exposeProxy" property on
046         * the controlling proxy configuration has been set to "true".
047         * @see ProxyConfig#setExposeProxy
048         */
049        private static final ThreadLocal<Object> currentProxy = new NamedThreadLocal<Object>("Current AOP proxy");
050
051
052        /**
053         * Try to return the current AOP proxy. This method is usable only if the
054         * calling method has been invoked via AOP, and the AOP framework has been set
055         * to expose proxies. Otherwise, this method will throw an IllegalStateException.
056         * @return Object the current AOP proxy (never returns {@code null})
057         * @throws IllegalStateException if the proxy cannot be found, because the
058         * method was invoked outside an AOP invocation context, or because the
059         * AOP framework has not been configured to expose the proxy
060         */
061        public static Object currentProxy() throws IllegalStateException {
062                Object proxy = currentProxy.get();
063                if (proxy == null) {
064                        throw new IllegalStateException(
065                                        "Cannot find current proxy: Set 'exposeProxy' property on Advised to 'true' to make it available.");
066                }
067                return proxy;
068        }
069
070        /**
071         * Make the given proxy available via the {@code currentProxy()} method.
072         * <p>Note that the caller should be careful to keep the old value as appropriate.
073         * @param proxy the proxy to expose (or {@code null} to reset it)
074         * @return the old proxy, which may be {@code null} if none was bound
075         * @see #currentProxy()
076         */
077        static Object setCurrentProxy(Object proxy) {
078                Object old = currentProxy.get();
079                if (proxy != null) {
080                        currentProxy.set(proxy);
081                }
082                else {
083                        currentProxy.remove();
084                }
085                return old;
086        }
087
088}