https://github.com/spring-projects/spring-framework: Spring AOP (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2020 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.

The 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 getEJBObject() can be used in EJBs. They can also use it to find advice configuration. 
Spring's AOP framework does not expose proxies by default, as there is a performance cost
in doing so.

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, Juergen Hoeller
Since:13.03.2003
/**
 * 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 null unless the "exposeProxy" property on the controlling proxy configuration has been set to "true". 
See Also:
/**
	 * 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.

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
Returns:the current AOP proxy (never returns null)
/**
	 * 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, and " +
							"ensure that AopContext.currentProxy() is invoked in the same thread as the AOP invocation context.");
		}
		return proxy;
	}

	
Make the given proxy available via the currentProxy() method. 
Note that the caller should be careful to keep the old value as appropriate.

Params:
  • proxy – the proxy to expose (or null to reset it)
See Also:
Returns:the old proxy, which may be null if none was bound
/**
	 * 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;
	}

}