/*
 * 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
 *
 *      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.transaction.interceptor;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.aop.support.AopUtils;
import org.springframework.core.MethodClassKey;
import org.springframework.lang.Nullable;
import org.springframework.util.ClassUtils;

Abstract implementation of TransactionAttributeSource that caches attributes for methods and implements a fallback policy: 1. specific target method; 2. target class; 3. declaring method; 4. declaring class/interface. 
Defaults to using the target class's transaction attribute if none is
associated with the target method. Any transaction attribute associated with
the target method completely overrides a class transaction attribute.
If none found on the target class, the interface that the invoked method
has been called through (in case of a JDK proxy) will be checked.
This implementation caches attributes by method after they are first used.
If it is ever desirable to allow dynamic changing of transaction attributes
(which is very unlikely), caching could be made configurable. Caching is
desirable because of the cost of evaluating rollback rules.
Author:
Rod Johnson, Juergen Hoeller
Since:
1.1/**
 * Abstract implementation of {@link TransactionAttributeSource} that caches
 * attributes for methods and implements a fallback policy: 1. specific target
 * method; 2. target class; 3. declaring method; 4. declaring class/interface.
 *
 * <p>Defaults to using the target class's transaction attribute if none is
 * associated with the target method. Any transaction attribute associated with
 * the target method completely overrides a class transaction attribute.
 * If none found on the target class, the interface that the invoked method
 * has been called through (in case of a JDK proxy) will be checked.
 *
 * <p>This implementation caches attributes by method after they are first used.
 * If it is ever desirable to allow dynamic changing of transaction attributes
 * (which is very unlikely), caching could be made configurable. Caching is
 * desirable because of the cost of evaluating rollback rules.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 1.1
 */
public abstract class AbstractFallbackTransactionAttributeSource implements TransactionAttributeSource {

	
Canonical value held in cache to indicate no transaction attribute was
found for this method, and we don't need to look again.
/**
	 * Canonical value held in cache to indicate no transaction attribute was
	 * found for this method, and we don't need to look again.
	 */
	@SuppressWarnings("serial")
	private static final TransactionAttribute NULL_TRANSACTION_ATTRIBUTE = new DefaultTransactionAttribute() {
		@Override
		public String toString() {
			return "null";
		}
	};


	
Logger available to subclasses.
As this base class is not marked Serializable, the logger will be recreated
after serialization - provided that the concrete subclass is Serializable.
/**
	 * Logger available to subclasses.
	 * <p>As this base class is not marked Serializable, the logger will be recreated
	 * after serialization - provided that the concrete subclass is Serializable.
	 */
	protected final Log logger = LogFactory.getLog(getClass());

	
Cache of TransactionAttributes, keyed by method on a specific target class.
As this base class is not marked Serializable, the cache will be recreated
after serialization - provided that the concrete subclass is Serializable.
/**
	 * Cache of TransactionAttributes, keyed by method on a specific target class.
	 * <p>As this base class is not marked Serializable, the cache will be recreated
	 * after serialization - provided that the concrete subclass is Serializable.
	 */
	private final Map<Object, TransactionAttribute> attributeCache = new ConcurrentHashMap<>(1024);


	
Determine the transaction attribute for this method invocation.
Defaults to the class's transaction attribute if no method attribute is found.
Params:
method – the method for the current invocation (never null)
targetClass – the target class for this invocation (may be null)
Returns:
a TransactionAttribute for this method, or null if the method is not transactional/**
	 * Determine the transaction attribute for this method invocation.
	 * <p>Defaults to the class's transaction attribute if no method attribute is found.
	 * @param method the method for the current invocation (never {@code null})
	 * @param targetClass the target class for this invocation (may be {@code null})
	 * @return a TransactionAttribute for this method, or {@code null} if the method
	 * is not transactional
	 */
	@Override
	@Nullable
	public TransactionAttribute getTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
		if (method.getDeclaringClass() == Object.class) {
			return null;
		}

		// First, see if we have a cached value.
		Object cacheKey = getCacheKey(method, targetClass);
		TransactionAttribute cached = this.attributeCache.get(cacheKey);
		if (cached != null) {
			// Value will either be canonical value indicating there is no transaction attribute,
			// or an actual transaction attribute.
			if (cached == NULL_TRANSACTION_ATTRIBUTE) {
				return null;
			}
			else {
				return cached;
			}
		}
		else {
			// We need to work it out.
			TransactionAttribute txAttr = computeTransactionAttribute(method, targetClass);
			// Put it in the cache.
			if (txAttr == null) {
				this.attributeCache.put(cacheKey, NULL_TRANSACTION_ATTRIBUTE);
			}
			else {
				String methodIdentification = ClassUtils.getQualifiedMethodName(method, targetClass);
				if (txAttr instanceof DefaultTransactionAttribute) {
					((DefaultTransactionAttribute) txAttr).setDescriptor(methodIdentification);
				}
				if (logger.isTraceEnabled()) {
					logger.trace("Adding transactional method '" + methodIdentification + "' with attribute: " + txAttr);
				}
				this.attributeCache.put(cacheKey, txAttr);
			}
			return txAttr;
		}
	}

	
Determine a cache key for the given method and target class.
Must not produce same key for overloaded methods.
Must produce same key for different instances of the same method.
Params:
method – the method (never null)
targetClass – the target class (may be null)
Returns:
the cache key (never null)/**
	 * Determine a cache key for the given method and target class.
	 * <p>Must not produce same key for overloaded methods.
	 * Must produce same key for different instances of the same method.
	 * @param method the method (never {@code null})
	 * @param targetClass the target class (may be {@code null})
	 * @return the cache key (never {@code null})
	 */
	protected Object getCacheKey(Method method, @Nullable Class<?> targetClass) {
		return new MethodClassKey(method, targetClass);
	}

	
Same signature as getTransactionAttribute, but doesn't cache the result. getTransactionAttribute is effectively a caching decorator for this method. 
As of 4.1.8, this method can be overridden.
See Also:
getTransactionAttribute
Since:
4.1.8/**
	 * Same signature as {@link #getTransactionAttribute}, but doesn't cache the result.
	 * {@link #getTransactionAttribute} is effectively a caching decorator for this method.
	 * <p>As of 4.1.8, this method can be overridden.
	 * @since 4.1.8
	 * @see #getTransactionAttribute
	 */
	@Nullable
	protected TransactionAttribute computeTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
		// Don't allow no-public methods as required.
		if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
			return null;
		}

		// The method may be on an interface, but we need attributes from the target class.
		// If the target class is null, the method will be unchanged.
		Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);

		// First try is the method in the target class.
		TransactionAttribute txAttr = findTransactionAttribute(specificMethod);
		if (txAttr != null) {
			return txAttr;
		}

		// Second try is the transaction attribute on the target class.
		txAttr = findTransactionAttribute(specificMethod.getDeclaringClass());
		if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
			return txAttr;
		}

		if (specificMethod != method) {
			// Fallback is to look at the original method.
			txAttr = findTransactionAttribute(method);
			if (txAttr != null) {
				return txAttr;
			}
			// Last fallback is the class of the original method.
			txAttr = findTransactionAttribute(method.getDeclaringClass());
			if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
				return txAttr;
			}
		}

		return null;
	}


	
Subclasses need to implement this to return the transaction attribute for the
given class, if any.
Params:
clazz – the class to retrieve the attribute for
Returns:
all transaction attribute associated with this class, or null if none/**
	 * Subclasses need to implement this to return the transaction attribute for the
	 * given class, if any.
	 * @param clazz the class to retrieve the attribute for
	 * @return all transaction attribute associated with this class, or {@code null} if none
	 */
	@Nullable
	protected abstract TransactionAttribute findTransactionAttribute(Class<?> clazz);

	
Subclasses need to implement this to return the transaction attribute for the
given method, if any.
Params:
method – the method to retrieve the attribute for
Returns:
all transaction attribute associated with this method, or null if none/**
	 * Subclasses need to implement this to return the transaction attribute for the
	 * given method, if any.
	 * @param method the method to retrieve the attribute for
	 * @return all transaction attribute associated with this method, or {@code null} if none
	 */
	@Nullable
	protected abstract TransactionAttribute findTransactionAttribute(Method method);

	
Should only public methods be allowed to have transactional semantics?
The default implementation returns false. /**
	 * Should only public methods be allowed to have transactional semantics?
	 * <p>The default implementation returns {@code false}.
	 */
	protected boolean allowPublicMethodsOnly() {
		return false;
	}

}