Spring AOP @Aspect Ordering Example

In Spring AOP, an aspect is a modular unit encapsulating cross-cutting concerns such as logging, security, or transaction management. We can define multiple aspects in an application and they can get executed at certain points in the application’s lifecycle, often referred to as join points.

Though it may not be needed in most cases, in this article, we’ll explore different ways to achieve aspect ordering in Spring AOP.

1. Why do we need Aspect Ordering?

Take a hypothetical scenario. We have two aspects, LoggingAspect and SecurityAspect, both intercepting method calls within a service package. The logging aspect should be executed before the security aspect to ensure that comprehensive logs are generated before security checks are performed.

Similarly, we may have CacheAspect and SecurityAspect in the application. The caching aspect should execute first to potentially retrieve results from the cache before security checks are repeated.

In these cases, it is necessary to enforce the aspect ordering explicitly.

2. Specifying Aspects Ordering

2.1. Using the @Order Annotation

One straightforward method to define the order of execution for aspects is by leveraging the @Order annotation. Aspects with lower order values are executed first.

• Aspects that have the same order value will be sorted with arbitrary ordering with respect to other objects with the same order value.
• Any aspect that does not provide its own order value is implicitly assigned a value of Ordered.LOWEST_PRECEDENCE, thus executed after all the ordered aspects have been executed.

Let’s consider two aspects, MyAspect1 and MyAspect2, where MyAspect1 should execute before MyAspect2.

@Aspect
@Order(1)
@Component
public class MyAspect1 {
    // Executes first
}

@Aspect
@Order(2)
@Component
public class MyAspect2 {
    // Executes later
}

2.2. Implementing the Ordered Interface

Another approach to aspect ordering is by implementing the Ordered interface. This provides more control over the order values assigned to the aspects.

import org.springframework.core.Ordered;

@Aspect
@Component
public class MyAspect1 implements Ordered {
    @Override
    public int getOrder() {
        return 1;
    }
    // Executes first
}

@Aspect
@Component
public class MyAspect2 implements Ordered {
    @Override
    public int getOrder() {
        return 2;
    }
    // Executes later
}

Implementing Ordered allows us to dynamically set the order value based on specific criteria or runtime conditions.

3. Demo

For demo purposes, we are creating two aspects LoggingAspect and SecurityAspect. We aim to execute LoggingAspect before SecurityAspect.

Here the @Order(1) annotation signifies that the logging aspect should be executed first.

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.core.annotation.Order;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Aspect
@Order(1)
@Component
public class LoggingAspect {
    private static final Logger logger = LoggerFactory.getLogger(LoggingAspect.class);

    @Before("execution(* com.example.service.*.*(..))")
    public void logBefore() {

        logger.info("LoggingAspect: Logging before method execution");
        // Logging logic
    }
}

The @Order(2) annotation signifies that the security aspect should be executed second.

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.core.annotation.Order;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Aspect
@Order(2)
@Component
public class SecurityAspect {
    private static final Logger logger = LoggerFactory.getLogger(SecurityAspect.class);

    @Before("execution(* com.example.service.*.*(..))")
    public void checkSecurity() {

        logger.info("SecurityAspect: Performing security check before method execution");
        // Security check logic
    }
}

Now we can run the application and execute a method in any class in the ‘com.howtodoinjava.service‘ package. It will trigger both aspects in the desired order that we can validate from the logs.

INFO  LoggingAspect: Logging before method execution
INFO  SecurityAspect: Performing security check before method execution

Great. Spring AOP aspects ordering is working as expected.

4. Conclusion

In this Spring AOP tutorial, we explored the fundamental concepts of aspects and discussed a few common problems requiring aspect ordering. By utilizing either the @Order annotation or implementing the Ordered interface, we can tailor the execution order of aspects to meet the specific needs of their applications.

Happy Learning !!