关于spring aop Advisor排序问题

关于spring aop Advisor排序问题

当我们使用多个Advisor的时候有时候需要排序，这时候可以用注解org.springframework.core.annotation.Order或者实现org.springframework.core.Ordered接口。

示例代码：

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;

/**
 * @author yaojiafeng
 * @create 2017-09-11 下午3:32
 */
@Aspect
@Order(1)
public class LogAspect implements Ordered {

    Logger logger = LoggerFactory.getLogger(LogAspect.class);

    @Pointcut("@annotation(com.yaojiafeng.test.aop.LogMDC)")
    public void log() {

    }

    @Around("log()")
    public Object log(ProceedingJoinPoint proceedingJoinPoint) throws Throwable {
        String interfaceName = proceedingJoinPoint.getTarget().getClass().getName();
        String methodName = proceedingJoinPoint.getSignature().getName();
        Object[] args = proceedingJoinPoint.getArgs();
        Object obj = null;
        try {
            obj = proceedingJoinPoint.proceed();
        } finally {
            logger.info(interfaceName + "-" + methodName + "-" + obj + "-" + args);
        }
        return obj;
    }

    @Override
    public int getOrder() {
        return 1;
    }
}

spring aop会在AnnotationAwareAspectJAutoProxyCreator处理bean查找到适配的Advisor的时候对所有Advisor进行排序并生成动态代理，AspectJAwareAdvisorAutoProxyCreator的sortAdvisors方法

@Override
	@SuppressWarnings("unchecked")
	protected List<Advisor> sortAdvisors(List<Advisor> advisors) {
		List<PartiallyComparableAdvisorHolder> partiallyComparableAdvisors =
				new ArrayList<PartiallyComparableAdvisorHolder>(advisors.size());
		for (Advisor element : advisors) {
			partiallyComparableAdvisors.add(
					new PartiallyComparableAdvisorHolder(element, DEFAULT_PRECEDENCE_COMPARATOR));
		}
		List<PartiallyComparableAdvisorHolder> sorted =
				PartialOrder.sort(partiallyComparableAdvisors);
		if (sorted != null) {
			List<Advisor> result = new ArrayList<Advisor>(advisors.size());
			for (PartiallyComparableAdvisorHolder pcAdvisor : sorted) {
				result.add(pcAdvisor.getAdvisor());
			}
			return result;
		}
		else {
			return super.sortAdvisors(advisors);
		}
	}

这里会根据每个Advisor的获取到的order值进行从小到大排序，order值获取规则如下：

1. 首先判断当前Advisor所在的切面类是否实现org.springframework.core.Ordered接口，是的话调用getOrder方法获取
2. 否则判断当前Advisor所在的切面类是否包含org.springframework.core.annotation.Order注解，是的话从注解获取
3. 没有取到值，默认为最低优先级，值为最大Int

从排序代码可知，有以下处理过程：

1. 打在Advice方法上的org.springframework.core.annotation.Order注解不予识别
2. 如果一个切面类存在多个Advisor，则会按Advice方法的声明顺序，声明在前的优先级高，先执行
3. 不同切面类但是order值是一样的，则按spring获取到切面bean的顺序做排序，先获取先执行