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/* * Copyright 2002-2018 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.aop.framework; import org.springframework.core.NamedThreadLocal; import org.springframework.lang.Nullable; /** * Class containing static methods used to obtain information about the current AOP invocation. * * <p>The {@code currentProxy()} method is usable if the AOP framework is configured to * expose the current proxy (not the default). It returns the AOP proxy in use. Target objects * or advice can use this to make advised calls, in the same way as {@code getEJBObject()} * can be used in EJBs. They can also use it to find advice configuration. * * <p>Spring's AOP framework does not expose proxies by default, as there is a performance cost * in doing so. * * <p>The functionality in this class might be used by a target object that needed access * to resources on the invocation. However, this approach should not be used when there is * a reasonable alternative, as it makes application code dependent on usage under AOP and * the Spring AOP framework in particular. * * @author Rod Johnson * @author Juergen Hoeller * @since 13.03.2003 */ public final class AopContext { /** * ThreadLocal holder for AOP proxy associated with this thread. * Will contain {@code null} unless the "exposeProxy" property on * the controlling proxy configuration has been set to "true". * @see ProxyConfig#setExposeProxy */ private static final ThreadLocal<Object> currentProxy = new NamedThreadLocal<>("Current AOP proxy"); private AopContext() { } /** * Try to return the current AOP proxy. This method is usable only if the * calling method has been invoked via AOP, and the AOP framework has been set * to expose proxies. Otherwise, this method will throw an IllegalStateException. * @return the current AOP proxy (never returns {@code null}) * @throws IllegalStateException if the proxy cannot be found, because the * method was invoked outside an AOP invocation context, or because the * AOP framework has not been configured to expose the proxy */ public static Object currentProxy() throws IllegalStateException { Object proxy = currentProxy.get(); if (proxy == null) { throw new IllegalStateException( "Cannot find current proxy: Set 'exposeProxy' property on Advised to 'true' to make it available."); } return proxy; } /** * Make the given proxy available via the {@code currentProxy()} method. * <p>Note that the caller should be careful to keep the old value as appropriate. * @param proxy the proxy to expose (or {@code null} to reset it) * @return the old proxy, which may be {@code null} if none was bound * @see #currentProxy() */ @Nullable static Object setCurrentProxy(@Nullable Object proxy) { Object old = currentProxy.get(); if (proxy != null) { currentProxy.set(proxy); } else { currentProxy.remove(); } return old; } }