Singleton from a FactoryBean may be post-processed twice if the first post-processing triggers a second attempt to get the bean [SPR-16783]

[spring-projects-issues]

Andy Wilkinson opened SPR-16783 and commented

Please see the referenced Spring Boot issue for my analysis of the failure and a sample project that can reproduce it.

I've also tried to create a more minimal reproduction of the problem. I've managed to reproduce a similar failure, but not the exact same one. The following code will fail when run:

package com.example.demo;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;

public class DuplicatePostProcessing {

	@Bean
	public ExampleFactoryBean exampleFactory() {
		return new ExampleFactoryBean();
	}

	@Bean
	public static ExampleBeanPostProcessor exampleBeanPostProcessor() {
		return new ExampleBeanPostProcessor();
	}

	@Bean
	public ExampleApplicationEventListener exampleApplicationEventListener() {
		return new ExampleApplicationEventListener();
	}

	public static void main(String[] args) {
		new AnnotationConfigApplicationContext(DuplicatePostProcessing.class).getBean(ExampleBean.class);
	}

	static class ExampleFactoryBean implements FactoryBean<ExampleBean> {

		private final ExampleBean exampleBean = new ExampleBean();

		@Override
		public ExampleBean getObject() throws Exception {
			return this.exampleBean;
		}

		@Override
		public Class<?> getObjectType() {
			return ExampleBean.class;
		}

		@Override
		public boolean isSingleton() {
			return true;
		}

	}

	static class ExampleBeanPostProcessor implements BeanPostProcessor, ApplicationContextAware {

		private ApplicationContext applicationContext;


		@Override
		public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
			return bean;
		}

		@Override
		public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
			if (bean instanceof ExampleBean) {
				this.applicationContext.publishEvent(new ExampleApplicationEvent(this));
			}
			return bean;
		}

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

	}

	static class ExampleApplicationEvent extends ApplicationEvent {

		public ExampleApplicationEvent(Object source) {
			super(source);
		}

	}

	static class ExampleApplicationEventListener implements ApplicationListener<ExampleApplicationEvent>, BeanFactoryAware {

		private BeanFactory beanFactory;

		@Override
		public void onApplicationEvent(ExampleApplicationEvent event) {
			this.beanFactory.getBean(ExampleBean.class);
		}

		@Override
		public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
			this.beanFactory = beanFactory;
		}

	}

	static class ExampleBean {

	}

}

It looks like it's blowing the stack but, rather than failing with a stack overflow, it outputs 400+ lines like the following:

16:44:30.704 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'exampleFactory'

It then fails with:

Exception in thread "main" java.lang.NoClassDefFoundError: Could not initialize class org.springframework.beans.factory.BeanCreationException
	at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:116)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1640)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:254)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:220)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:1018)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:345)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:340)
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1092)
	at com.example.demo.DuplicatePostProcessing.main(DuplicatePostProcessing.java:33)

---

Affects: 4.3.16, 5.0.5

Reference URL: spring-projects/spring-boot#12280

Referenced from: commits 9281f82, be4c07f, fbd8301

Backported to: 4.3.17

0 votes, 6 watchers

[spring-projects-issues]

Juergen Hoeller commented

We're doing that post-processing step within a singleton-currently-in-creation marker now, temporarily returning the FactoryBean's raw object on retrieval during post-processing. This should hopefully be good enough for such scenarios... Of course, the recommendation is to never access an object within its own post-processing phase to begin with.

[spring-projects-issues]

Juergen Hoeller commented

Andy Wilkinson, is there any feedback on this already? Not least of it all, no negative side effects from that change?

[spring-projects-issues]

Stéphane Nicoll commented

Juergen Hoeller I confirm that this change fixes the sample attached. The integration tests on our side are green as well.