/*
 * 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.interceptor;

import java.io.Serializable;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

import org.springframework.aop.Advisor;
import org.springframework.aop.support.DefaultPointcutAdvisor;
import org.springframework.core.NamedThreadLocal;
import org.springframework.core.PriorityOrdered;
import org.springframework.lang.Nullable;

Interceptor that exposes the current MethodInvocation as a thread-local object. We occasionally need to do this; for example, when a pointcut (e.g. an AspectJ expression pointcut) needs to know the full invocation context. 
Don't use this interceptor unless this is really necessary. Target objects should
not normally know about Spring AOP, as this creates a dependency on Spring API.
Target objects should be plain POJOs as far as possible.
If used, this interceptor will normally be the first in the interceptor chain.
Author:
Rod Johnson, Juergen Hoeller/**
 * Interceptor that exposes the current {@link org.aopalliance.intercept.MethodInvocation}
 * as a thread-local object. We occasionally need to do this; for example, when a pointcut
 * (e.g. an AspectJ expression pointcut) needs to know the full invocation context.
 *
 * <p>Don't use this interceptor unless this is really necessary. Target objects should
 * not normally know about Spring AOP, as this creates a dependency on Spring API.
 * Target objects should be plain POJOs as far as possible.
 *
 * <p>If used, this interceptor will normally be the first in the interceptor chain.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 */
@SuppressWarnings("serial")
public final class ExposeInvocationInterceptor implements MethodInterceptor, PriorityOrdered, Serializable {

	
Singleton instance of this class. /** Singleton instance of this class. */
	public static final ExposeInvocationInterceptor INSTANCE = new ExposeInvocationInterceptor();

	
Singleton advisor for this class. Use in preference to INSTANCE when using
Spring AOP, as it prevents the need to create a new Advisor to wrap the instance.
/**
	 * Singleton advisor for this class. Use in preference to INSTANCE when using
	 * Spring AOP, as it prevents the need to create a new Advisor to wrap the instance.
	 */
	public static final Advisor ADVISOR = new DefaultPointcutAdvisor(INSTANCE) {
		@Override
		public String toString() {
			return ExposeInvocationInterceptor.class.getName() +".ADVISOR";
		}
	};

	private static final ThreadLocal<MethodInvocation> invocation =
			new NamedThreadLocal<>("Current AOP method invocation");


	
Return the AOP Alliance MethodInvocation object associated with the current invocation.
Throws:
IllegalStateException – if there is no AOP invocation in progress,
or if the ExposeInvocationInterceptor was not added to this interceptor chain
Returns:
the invocation object associated with the current invocation/**
	 * Return the AOP Alliance MethodInvocation object associated with the current invocation.
	 * @return the invocation object associated with the current invocation
	 * @throws IllegalStateException if there is no AOP invocation in progress,
	 * or if the ExposeInvocationInterceptor was not added to this interceptor chain
	 */
	public static MethodInvocation currentInvocation() throws IllegalStateException {
		MethodInvocation mi = invocation.get();
		if (mi == null) {
			throw new IllegalStateException(
					"No MethodInvocation found: Check that an AOP invocation is in progress and that the " +
					"ExposeInvocationInterceptor is upfront in the interceptor chain. Specifically, note that " +
					"advices with order HIGHEST_PRECEDENCE will execute before ExposeInvocationInterceptor! " +
					"In addition, ExposeInvocationInterceptor and ExposeInvocationInterceptor.currentInvocation() " +
					"must be invoked from the same thread.");
		}
		return mi;
	}


	
Ensures that only the canonical instance can be created.
/**
	 * Ensures that only the canonical instance can be created.
	 */
	private ExposeInvocationInterceptor() {
	}

	@Override
	@Nullable
	public Object invoke(MethodInvocation mi) throws Throwable {
		MethodInvocation oldInvocation = invocation.get();
		invocation.set(mi);
		try {
			return mi.proceed();
		}
		finally {
			invocation.set(oldInvocation);
		}
	}

	@Override
	public int getOrder() {
		return PriorityOrdered.HIGHEST_PRECEDENCE + 1;
	}

	
Required to support serialization. Replaces with canonical instance
on deserialization, protecting Singleton pattern.
Alternative to overriding the equals method. /**
	 * Required to support serialization. Replaces with canonical instance
	 * on deserialization, protecting Singleton pattern.
	 * <p>Alternative to overriding the {@code equals} method.
	 */
	private Object readResolve() {
		return INSTANCE;
	}

}