Invalid WARN when returning a BeanDefinitionRegistryPostProcessor from within a @Configuration class [SPR-14603]

[spring-projects-issues]

Les Hazlewood opened SPR-14603 and commented

Consider the following configuration class:

import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MyConfiguration {

    @Bean
    public static BeanDefinitionRegistryPostProcessor myPostProcessor() {
        return new MyBeanDefinitionPostProcessor();
    }
}

(if it matters, this class is loaded in Spring MVC and Spring Boot applications via an @Import(MyConfiguration.class) annotation.)

This causes a WARN message to be printed as follows:

Cannot enhance @Configuration bean definition 'myPostProcessor' since its singleton instance has been created too early. The typical cause is a non-static @Bean method with a BeanDefinitionRegistryPostProcessor return type: Consider declaring such methods as 'static'.

As you can see, the method is declared as static, yet I still receive the WARN message. When I remove the static modifier, I still receive the same WARN message. Something is amiss.

This is a problem for us because we use this code in a Spring library as well as a Spring Boot starter/plugin that we distribute to customers - when they see the WARN message, they think something is wrong, even though everything is working as expected.

---

Issue Links:

• #15258 Allow BeanDefinitionRegistryPostProcessor to register other BeanDefinitionRegistryPostProcessors

[spring-projects-issues]

Les Hazlewood commented

I commented out the @Import approach and tried as a nested static class to see if that would help:

//@Import(MyConfiguration.class)
@Configuration
public class SomeConfiguration {

    @Configuration
    public static class MyConfiguration {
        @Bean
        public static BeanDefinitionRegistryPostProcessor myPostProcessor() {
            return new MyBeanDefinitionPostProcessor();
        }
    }

    //other non-relevant @Bean definitions here...
}

This didn't work either - same WARN message.

[spring-projects-issues]

Juergen Hoeller commented

What does your post-processor implementation class look like? The warn message suggests that the post-processor class itself is marked with @Configuration...

[spring-projects-issues]

Thomas Vahrst commented

I get the same warning, when I try to define a BeanDefinitionRegistryPostProcessor as static @Bean method. It seems, thas every BeanDefinition of static defined Beans gets an BeanDefinition attribute org.springframework.context.annotation.ConfigurationClassPostProcessor.configurationClass = full, because

in ConfigClassBeanDefinitionReader :

	private void loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) {
..
		if (metadata.isStatic()) {
			// static @Bean method
			beanDef.setBeanClassName(configClass.getMetadata().getClassName());
			beanDef.setFactoryMethodName(methodName);
		}
		else {

The beanClassName in the beandefinition is set to configClass' classname

and later in ConfigurationClassUtils:

	public static boolean checkConfigurationClassCandidate(BeanDefinition beanDef, MetadataReaderFactory metadataReaderFactory) {

...
		if (isFullConfigurationCandidate(metadata)) {
			beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);
		}

This seems not to be problem for 'normal' beans, but if the bean type is BeanDefinitionRegistryFactoryPostProcessor, it is instantiated very early. This in turn leads to the warning in ConfigurationClassPostProcessor.enhanceConfigurationClasses becauce both conditions

• .isFullConfigurationClass AND
• beanFactory.containsSinglenton
  are true.

[spring-projects-issues]

Thomas Vahrst commented

Our workaround:
put the BeanDefinitionPostProcessor class in a special sub-package, annotate it with @Component und define @ComponentScan(basePackages=...) in the config class.