001/*
002 * Copyright 2002-2020 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;
020import org.springframework.lang.Nullable;
021
022/**
023 * Class containing static methods used to obtain information about the current AOP invocation.
024 *
025 * <p>The {@code currentProxy()} method is usable if the AOP framework is configured to
026 * expose the current proxy (not the default). It returns the AOP proxy in use. Target objects
027 * or advice can use this to make advised calls, in the same way as {@code getEJBObject()}
028 * can be used in EJBs. They can also use it to find advice configuration.
029 *
030 * <p>Spring's AOP framework does not expose proxies by default, as there is a performance cost
031 * in doing so.
032 *
033 * <p>The functionality in this class might be used by a target object that needed access
034 * to resources on the invocation. However, this approach should not be used when there is
035 * a reasonable alternative, as it makes application code dependent on usage under AOP and
036 * the Spring AOP framework in particular.
037 *
038 * @author Rod Johnson
039 * @author Juergen Hoeller
040 * @since 13.03.2003
041 */
042public final class AopContext {
043
044        /**
045         * ThreadLocal holder for AOP proxy associated with this thread.
046         * Will contain {@code null} unless the "exposeProxy" property on
047         * the controlling proxy configuration has been set to "true".
048         * @see ProxyConfig#setExposeProxy
049         */
050        private static final ThreadLocal<Object> currentProxy = new NamedThreadLocal<>("Current AOP proxy");
051
052
053        private AopContext() {
054        }
055
056
057        /**
058         * Try to return the current AOP proxy. This method is usable only if the
059         * calling method has been invoked via AOP, and the AOP framework has been set
060         * to expose proxies. Otherwise, this method will throw an IllegalStateException.
061         * @return the current AOP proxy (never returns {@code null})
062         * @throws IllegalStateException if the proxy cannot be found, because the
063         * method was invoked outside an AOP invocation context, or because the
064         * AOP framework has not been configured to expose the proxy
065         */
066        public static Object currentProxy() throws IllegalStateException {
067                Object proxy = currentProxy.get();
068                if (proxy == null) {
069                        throw new IllegalStateException(
070                                        "Cannot find current proxy: Set 'exposeProxy' property on Advised to 'true' to make it available, and " +
071                                                        "ensure that AopContext.currentProxy() is invoked in the same thread as the AOP invocation context.");
072                }
073                return proxy;
074        }
075
076        /**
077         * Make the given proxy available via the {@code currentProxy()} method.
078         * <p>Note that the caller should be careful to keep the old value as appropriate.
079         * @param proxy the proxy to expose (or {@code null} to reset it)
080         * @return the old proxy, which may be {@code null} if none was bound
081         * @see #currentProxy()
082         */
083        @Nullable
084        static Object setCurrentProxy(@Nullable Object proxy) {
085                Object old = currentProxy.get();
086                if (proxy != null) {
087                        currentProxy.set(proxy);
088                }
089                else {
090                        currentProxy.remove();
091                }
092                return old;
093        }
094
095}