/*
* Copyright 2002-2010 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
*
* http://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;
/**
* Class containing static methods used to obtain information about the current AOP invocation.
*
* <p>The <code>currentProxy()</code> 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()</code>
* 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 abstract class AopContext {
/**
* ThreadLocal holder for AOP proxy associated with this thread.
* Will contain <code>null</code> 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<Object>("Current AOP proxy");
/**
* 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 Object the current AOP proxy (never returns <code>null</code>)
* @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()</code> 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</code> to reset it)
* @return the old proxy, which may be <code>null</code> if none was bound
* @see #currentProxy()
*/
static Object setCurrentProxy(Object proxy) {
Object old = currentProxy.get();
if (proxy != null) {
currentProxy.set(proxy);
}
else {
currentProxy.remove();
}
return old;
}
}
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