abstractfallbacktransactionattributesource.java

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/*
 * Copyright 2002-2007 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.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

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

import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;

/**
 * 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.
	 */
	private final static Object NULL_TRANSACTION_ATTRIBUTE = new Object();


	/**
	 * 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 DefaultCacheKey (Method + 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.
	 */
	final Map attributeCache = new HashMap();


	/**
	 * 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</code>)
	 * @param targetClass the target class for this invocation (may be <code>null</code>)
	 * @return TransactionAttribute for this method, or <code>null</code> if the method
	 * is not transactional
	 */
	public TransactionAttribute getTransactionAttribute(Method method, Class targetClass) {
		// First, see if we have a cached value.
		Object cacheKey = getCacheKey(method, targetClass);
		synchronized (this.attributeCache) {
			Object 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 (TransactionAttribute) cached;
				}
			}
			else {
				// We need to work it out.
				TransactionAttribute txAtt = computeTransactionAttribute(method, targetClass);
				// Put it in the cache.
				if (txAtt == null) {
					this.attributeCache.put(cacheKey, NULL_TRANSACTION_ATTRIBUTE);
				}
				else {
					if (logger.isDebugEnabled()) {
						logger.debug("Adding transactional method [" + method.getName() + "] with attribute [" + txAtt + "]");
					}
					this.attributeCache.put(cacheKey, txAtt);
				}
				return txAtt;
			}
		}
	}

	/**
	 * 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</code>)
	 * @param targetClass the target class (may be <code>null</code>)
	 * @return the cache key (never <code>null</code>)
	 */
	protected Object getCacheKey(Method method, Class targetClass) {
		return new DefaultCacheKey(method, targetClass);
	}

	/**
	 * Same signature as {@link #getTransactionAttribute}, but doesn't cache the result.
	 * {@link #getTransactionAttribute} is effectively a caching decorator for this method.
	 * @see #getTransactionAttribute
	 */
	private TransactionAttribute computeTransactionAttribute(Method method, 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 = ClassUtils.getMostSpecificMethod(method, targetClass);

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

		// Second try is the transaction attribute on the target class.
		txAtt = findTransactionAttribute(findAllAttributes(specificMethod.getDeclaringClass()));
		if (txAtt != null) {
			return txAtt;
		}

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


	/**
	 * Subclasses should implement this to return all attributes for this method.
	 * We need all because of the need to analyze rollback rules.
	 * @param method the method to retrieve attributes for
	 * @return all attributes associated with this method (may be <code>null</code>)
	 */
	protected abstract Collection findAllAttributes(Method method);
	
	/**
	 * Subclasses should implement this to return all attributes for this class.	 
	 * @param clazz class to retrieve attributes for
	 * @return all attributes associated with this class (may be <code>null</code>)
	 */
	protected abstract Collection findAllAttributes(Class clazz);


	/**
	 * Return the transaction attribute, given this set of attributes
	 * attached to a method or class.
	 * <p>Protected rather than private as subclasses may want to customize
	 * how this is done: for example, returning a TransactionAttribute
	 * affected by the values of other attributes.
	 * <p>This implementation takes into account RollbackRuleAttributes,
	 * if the TransactionAttribute is a RuleBasedTransactionAttribute.
	 * @param atts attributes attached to a method or class (may be <code>null</code>)
	 * @return TransactionAttribute the corresponding transaction attribute,
	 * or <code>null</code> if none was found
	 */
	protected TransactionAttribute findTransactionAttribute(Collection atts) {
		if (atts == null) {
			return null;
		}

		TransactionAttribute txAttribute = null;

		// Check whether there is a transaction attribute.
		for (Iterator itr = atts.iterator(); itr.hasNext() && txAttribute == null; ) {
			Object att = itr.next();
			if (att instanceof TransactionAttribute) {
				txAttribute = (TransactionAttribute) att;
			}
		}

		// Check if we have a RuleBasedTransactionAttribute.
		if (txAttribute instanceof RuleBasedTransactionAttribute) {
			RuleBasedTransactionAttribute rbta = (RuleBasedTransactionAttribute) txAttribute;
			// We really want value: bit of a hack.
			List rollbackRules = new LinkedList();
			for (Iterator it = atts.iterator(); it.hasNext(); ) {
				Object att = it.next();
				if (att instanceof RollbackRuleAttribute) {
					if (logger.isDebugEnabled()) {
						logger.debug("Found rollback rule: " + att);
					}
					rollbackRules.add(att);
				}
			}
			// Repeatedly setting this isn't elegant, but it works.
			rbta.setRollbackRules(rollbackRules);
		}
		
		return txAttribute;
	}

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


	/**
	 * Default cache key for the TransactionAttribute cache.
	 */
	private static class DefaultCacheKey {

		private final Method method;

		private final Class targetClass;

		public DefaultCacheKey(Method method, Class targetClass) {
			this.method = method;
			this.targetClass = targetClass;
		}

		public boolean equals(Object other) {
			if (this == other) {
				return true;
			}
			if (!(other instanceof DefaultCacheKey)) {
				return false;
			}
			DefaultCacheKey otherKey = (DefaultCacheKey) other;
			return (this.method.equals(otherKey.method) &&
					ObjectUtils.nullSafeEquals(this.targetClass, otherKey.targetClass));
		}

		public int hashCode() {
			return this.method.hashCode() * 29 + (this.targetClass != null ? this.targetClass.hashCode() : 0);
		}
	}

}