aspectjprecedencecomparator.java

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/*
 * Copyright 2002-2006 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.aspectj.autoproxy;

import java.util.Comparator;

import org.springframework.aop.Advisor;
import org.springframework.aop.aspectj.AspectJAopUtils;
import org.springframework.aop.aspectj.AspectJPrecedenceInformation;
import org.springframework.core.OrderComparator;
import org.springframework.util.Assert;

/**
 * Orders AspectJ advice/advisors by precedence (<i>not</i> invocation order).
 *
 * <p>Given two pieces of advice, <code>a</code> and <code>b</code>:
 * <ul>
 *   <li>if <code>a</code> and <code>b</code> are defined in different
 *   aspects, then the advice in the aspect with the lowest order
 *   value has the highest precedence</li>
 *   <li>if <code>a</code> and <code>b</code> are defined in the same
 *   aspect, then if one of <code>a</code> or <code>b</code> is a form of
 *   after advice, then the advice declared last in the aspect has the
 *   highest precedence. If neither <code>a</code> nor <code>b</code> is a
 *   form of after advice, then the advice declared first in the aspect has
 *   the highest precedence.</li>
 * </ul>
 *
 * <p>Important: Note that unlike a normal comparator a return of 0 means
 * we don't care about the ordering, not that the two elements must be sorted
 * identically. Used with AspectJ PartialOrder class.
 *
 * @author Adrian Colyer
 * @author Juergen Hoeller
 * @since 2.0
 */
class AspectJPrecedenceComparator implements Comparator {

	private static final int HIGHER_PRECEDENCE = -1;
	private static final int SAME_PRECEDENCE = 0;
	private static final int LOWER_PRECEDENCE = 1;
	private static final int NOT_COMPARABLE = 0;

	private final Comparator advisorComparator;


	/**
	 * Create a default AspectJPrecedenceComparator.
	 */
	public AspectJPrecedenceComparator() {
		this.advisorComparator = new OrderComparator();
	}

	/**
	 * Create a AspectJPrecedenceComparator, using the given Comparator
	 * for comparing {@link org.springframework.aop.Advisor} instances.
	 * @param advisorComparator the Comparator to use for Advisors
	 */
	public AspectJPrecedenceComparator(Comparator advisorComparator) {
		Assert.notNull(advisorComparator, "Advisor comparator must not be null");
		this.advisorComparator = advisorComparator;
	}


	public int compare(Object o1, Object o2) {
		if (!(o1 instanceof Advisor && o2 instanceof Advisor)) {
			throw new IllegalArgumentException(
					"AspectJPrecedenceComparator can only compare the order of Advisors, " +
					"but was passed [" + o1 + "] and [" + o2 + "]");
		}

		Advisor advisor1 = (Advisor) o1;
		Advisor advisor2 = (Advisor) o2;

		boolean oneOrOtherIsAfterAdvice =
				(AspectJAopUtils.isAfterAdvice(advisor1) || AspectJAopUtils.isAfterAdvice(advisor2));
		boolean oneOrOtherIsBeforeAdvice =
				(AspectJAopUtils.isBeforeAdvice(advisor1) || AspectJAopUtils.isBeforeAdvice(advisor2));
		if (oneOrOtherIsAfterAdvice && oneOrOtherIsBeforeAdvice) {
			return NOT_COMPARABLE;
		}
		else {
			int advisorPrecedence = this.advisorComparator.compare(advisor1, advisor2);
			if (advisorPrecedence == SAME_PRECEDENCE && declaredInSameAspect(advisor1, advisor2)) {
				advisorPrecedence = comparePrecedenceWithinAspect(advisor1, advisor2);
			}
			return advisorPrecedence;
		}
	}

	private int comparePrecedenceWithinAspect(Advisor advisor1, Advisor advisor2) {
		boolean oneOrOtherIsAfterAdvice =
				(AspectJAopUtils.isAfterAdvice(advisor1) || AspectJAopUtils.isAfterAdvice(advisor2));
		int adviceDeclarationOrderDelta = getAspectDeclarationOrder(advisor1) - getAspectDeclarationOrder(advisor2);
		
		if (oneOrOtherIsAfterAdvice) {
			// the advice declared last has higher precedence
			if (adviceDeclarationOrderDelta < 0) {
				// advice1 was declared before advice2
				// so advice1 has lower precedence
				return LOWER_PRECEDENCE;
			} 
			else if (adviceDeclarationOrderDelta == 0) {
				return SAME_PRECEDENCE;
			}
			else {
				return HIGHER_PRECEDENCE;
			}
		}
		else {
			// the advice declared first has higher precedence
			if (adviceDeclarationOrderDelta < 0) {
				// advice1 was declared before advice2
				// so advice1 has higher precedence
				return HIGHER_PRECEDENCE;
			}
			else if (adviceDeclarationOrderDelta == 0) {
				return SAME_PRECEDENCE;
			}
			else {
				return LOWER_PRECEDENCE;
			}
		}
	}

	private boolean declaredInSameAspect(Advisor advisor1, Advisor advisor2) {
		if (!(hasAspectName(advisor1) && hasAspectName(advisor2))) {
			return false;
		}
		else {
			return getAspectName(advisor1).equals(getAspectName(advisor2));
		}
	}

	private boolean hasAspectName(Advisor anAdvisor) {
		return (anAdvisor instanceof AspectJPrecedenceInformation ||
				anAdvisor.getAdvice() instanceof AspectJPrecedenceInformation);
	}

	// pre-condition is that hasAspectName returned true
	private String getAspectName(Advisor anAdvisor) {
		return AspectJAopUtils.getAspectJPrecedenceInformationFor(anAdvisor).getAspectName();
	}

	private int getAspectDeclarationOrder(Advisor anAdvisor) {
		AspectJPrecedenceInformation precedenceInfo = 
			AspectJAopUtils.getAspectJPrecedenceInformationFor(anAdvisor);
		if (precedenceInfo != null) {
			return precedenceInfo.getDeclarationOrder();
		}
		else {
			return 0;
		}
	}

}