BeanNotOfRequiredTypeException if @Bean factory method returns null

[felipe-issa-zebra]

I've upgraded our app from spring 3.3.5 to 3.4.3 and on the newer version the app is throwing the following error on initialization:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.boot.actuate.autoconfigure.metrics.task.TaskExecutorMetricsAutoConfiguration': Injection of autowired dependencies failed
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:515) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1445) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:600) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:523) ~[spring-beans-6.2.3.jar:6.2.3]
	... many more
Caused by: org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'splitFilesTaskExecutor' is expected to be of type 'org.springframework.core.task.TaskExecutor' but was actually of type 'org.springframework.beans.factory.support.NullBean'
	at org.springframework.beans.factory.support.AbstractBeanFactory.adaptBeanInstance(AbstractBeanFactory.java:424) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:405) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:207) ~[spring-beans-6.2.3.jar:6.2.3]
	... many more

This spring bean is created the following way:

@Configuration
public class ProjectLauncherConfiguration {

	@Bean()
	public TaskExecutor splitFilesTaskExecutor() {
		if ( ** some logic ** ) {
			ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
			executor.setMaxPoolSize(splitMaxPoolSize);
			executor.setCorePoolSize(splitPoolSize);
			executor.setQueueCapacity(Integer.MAX_VALUE);
			return executor;
		}
		return null;
	}
}

If the bean is created, it works just fine. But when the scenario doesn't create the bean, the exception is thrown and the app is does not initialize.

[sbrannen]

Related discussion: #33792 (comment)

[jhoeller]

@felipe-issa-zebra could you share a bit more of the stacktrace? Specifically, the full stack inbetween the postProcessProperties call and the AbstractBeanFactory.getBean call in the cause?

While returning null from a factory method is not recommended, we intend to tolerate it for @Bean methods and @Autowired injection points. It looks like we have some accidental regression there in 6.2.

[felipe-issa-zebra]

Hi @jhoeller ,

Here is the complete stacktrace I have on intelij:

[ERROR] 2025-03-05 11:11:39,275  main o.s.b.SpringApplication.reportFailure - Application run failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.boot.actuate.autoconfigure.metrics.task.TaskExecutorMetricsAutoConfiguration': Injection of autowired dependencies failed
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:515) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1445) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:600) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:523) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:339) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:346) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:337) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.instantiateSingleton(DefaultListableBeanFactory.java:1155) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingleton(DefaultListableBeanFactory.java:1121) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:1056) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:987) ~[spring-context-6.2.3.jar:6.2.3]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:627) ~[spring-context-6.2.3.jar:6.2.3]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:146) ~[spring-boot-3.4.3.jar:3.4.3]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:752) [spring-boot-3.4.3.jar:3.4.3]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:439) [spring-boot-3.4.3.jar:3.4.3]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:318) [spring-boot-3.4.3.jar:3.4.3]
	at com.something.App.main(App.java:30) [classes/:?]
Caused by: org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'splitFilesTaskExecutor' is expected to be of type 'org.springframework.core.task.TaskExecutor' but was actually of type 'org.springframework.beans.factory.support.NullBean'
	at org.springframework.beans.factory.support.AbstractBeanFactory.adaptBeanInstance(AbstractBeanFactory.java:424) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:405) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:207) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.support.SimpleAutowireCandidateResolver.resolveAutowireCandidates(SimpleAutowireCandidateResolver.java:73) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.boot.actuate.autoconfigure.metrics.task.TaskExecutorMetricsAutoConfiguration.bindTaskExecutorsToRegistry(TaskExecutorMetricsAutoConfiguration.java:60) ~[spring-boot-actuator-autoconfigure-3.4.3.jar:3.4.3]
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103) ~[?:?]
	at java.base/java.lang.reflect.Method.invoke(Method.java:580) ~[?:?]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:854) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:146) ~[spring-beans-6.2.3.jar:6.2.3]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:509) ~[spring-beans-6.2.3.jar:6.2.3]
	... 17 more

[jhoeller]

Ah so it's in the 6.2.3-introduced SimpleAutowireCandidateResolver.resolveAutowireCandidates methods that Boot is using there. Indeed, we don't handle null beans in that particular new code path. I'll fix this for 6.2.4.