Spring autowired bean for @Aspect aspect is null

I have the following spring configuration:

<context:component-scan base-package="uk.co.mysite.googlecontactsync.aop"/>

<bean name="simpleEmailSender" class="uk.co.mysite.util.email.simple.SimpleEmailSenderImplementation"/>

<aop:aspectj-autoproxy/>

Then I have an aspect:

@Aspect
public class SyncLoggingAspect {
    @Autowired
    private SimpleEmailSender simpleEmailSender

    @AfterReturning(value="execution(* uk.co.mysite.datasync.polling.Poller+.doPoll())", returning="pusher")
    public void afterPoll(Pusher pusher) {      
        simpleEmailSender.send(new PusherEmail(pusher));
    }
}

This aspect works (I can hit a breakpoint on afterPoll) but simpleEmailSender is null. Unfortunately I cannot find clear documentation on why this is. (For the record, my simpleEmailSender bean exists and is correctly wired into other classes) The following things confuse me:

1. Is context:component-scan supposed to be picking up @Aspect? If it is then surely it would be a spring managed bean, thus autowired should work?
2. If context:component-scan isn't for creating aspects, how is my aspect being created? I thought aop:aspectj-autoproxy just creates a beanPostProcessor to proxy my @Aspect class? How would it do this if it isn't a spring managed bean?

Obviously you can tell I don't have an understanding of how things should be working from the ground up.

Solution 1:

The aspect is a singleton object and is created outside the Spring container. A solution with XML configuration is to use Spring's factory method to retrieve the aspect.

<bean id="syncLoggingAspect" class="uk.co.demo.SyncLoggingAspect" 
     factory-method="aspectOf" />

With this configuration the aspect will be treated as any other Spring bean and the autowiring will work as normal.

You have to use the factory-method also on Enum objects and other objects without a constructor or objects that are created outside the Spring container.

Solution 2:

Another option is to add @Configurable to your aspect class instead of messing around with XML.

Solution 3:

For Spring Boot to use @Autowired with AspectJ I have found the following method. In configuration class add your aspect:

@Configuration
@ComponentScan("com.kirillch.eqrul")
public class AspectConfig {

    @Bean
    public EmailAspect theAspect() {
        EmailAspect aspect = Aspects.aspectOf(EmailAspect.class);
        return aspect;
    }

}

Then you can successfully autowire your services in your aspect class:

@Aspect
public class EmailAspect {

    @Autowired
    EmailService emailService;

Solution 4:

Configuring @Autowired with java config only (so no XML based configuration) requires a bit of extra work than just adding @Configuration to the class, as it also needs the aspectOf method.

What worked for me was creating a new class:

@Component
public class SpringApplicationContextHolder implements ApplicationContextAware {

    private static ApplicationContext applicationContext = null;

    public static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
       this.applicationContext = applicationContext;
    }
}

And then use that in you aspect in conjunction with using @DependsOn @Configured and @Autowired:

@DependsOn("springApplicationContextHolder")
@Configuration
@Aspect
public class SomeAspect {

    @Autowired
    private SomeBean someBean;

    public static SomeAspect aspectOf() {
        return SpringApplicationContextHolder.getApplicationContext().getBean(SomeAspect.class);
    }

The @DependsOn is needed because spring can't determine the dependency because the bean is used staticly.