Strange behavior when trying to override @Bean method from parent class and rewrite the bean name

[Aimini]

Affects: 6.1.5

I was trying to override a @Bean method from the parent class but with a different bean name, I expected the here would only be one bean generated by method in child, but the result was weird and has something to do whether you are using @Import or @ComponentScan.

I know this is not a practical usage, but it's still an interesting and intriguing problem.

---

Example

package com.ai.demo.configtest;

public class MyTestBean {
    public MyTestBean(String msg) {
        this.msg = msg;
    }

    String msg;

    public String getMsg() {
        return msg;
    }
}

package com.ai.demo.configtest;

import org.springframework.context.annotation.Bean;

public class BeanInOverriddenParent {
    @Bean("ParentBean")
    MyTestBean getBeanOverridden() {
        return new MyTestBean("parent");
    }
}

package com.ai.demo.configtest;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class BeanOverridingChild extends BeanInOverriddenParent {

    @Bean("ChildBean")
    @Override
    MyTestBean getBeanOverridden() {
        return new MyTestBean("beanMethodOverriddenInChildBean");
    }
}

package com.ai.demo.configtest;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Configuration
@Import(BeanOverridingChild.class)
@ComponentScan(basePackageClasses = {TestMain.class})
public class TestMain {

    @Autowired
    MyTestBean[] myTestBeans;

    public TestMain() {

    }

    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(TestMain.class);
        TestMain bean = applicationContext.getBean(TestMain.class);
        for (MyTestBean myTestBean : bean.myTestBeans) {
            System.out.println(myTestBean.getMsg());
        }
    }
}

Case 1: only using @Import(BeanOverridingChild.class)

It produced two beans; the console output are like:

beanMethodOverriddenInChildBean
beanMethodOverriddenInChildBean

Case 2: only using @ComponentScan(basePackageClasses = {TestMain.class})

It thrown an BeanCreationException in following output:

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'ParentBean' defined in class path resource [com/ai/demo/configtest/BeanOverridingChild.class]: No matching factory method found on class [com.ai.demo.configtest.BeanOverridingChild]: factory bean 'beanOverridingChild'; factory method 'getBeanOverridden()'. Check that a method with the specified name exists and that it is non-static.
	at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:616)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1335)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1165)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:562)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:522)
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:326)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:324)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:200)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:975)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:962)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:624)
	at org.springframework.context.annotation.AnnotationConfigApplicationContext.<init>(AnnotationConfigApplicationContext.java:93)
	at com.ai.demo.configtest.TestMain.main(TestMain.java:22)

[Aimini]

The case 1 isn't hard to understand since I found that the bean definitions is registered into DefaultListableBeanFactory.beanDefinitionMap by name, And the ConfigurationCLassParser generates two bean methods within ConfigurationClass object, which has different name.

But the case 2 is more interesting since it prefer to throw exception and it actually says here is no proper 'getBeanOverridden()'. to construct it.

---

After some code-digging I found it's has something to do with the code below at line 460

spring-framework/spring-beans/src/main/java/org/springframework/beans/factory/support/ConstructorResolver.java

Lines 459 to 461 in c04290e

	if (factoryMethodToUse == null) {
	factoryMethodToUse = mbd.getResolvedFactoryMethod();
	}

In the first case it gets a Method Object and it's com.ai.demo.configtest.MyTestBean com.ai.demo.configtest.BeanInOverriddenParent.getBeanOverridden(),

In the second case it gets a null, so the program continues to the

spring-framework/spring-beans/src/main/java/org/springframework/beans/factory/support/ConstructorResolver.java

Lines 466 to 474 in c04290e

	if (candidates == null) {
	candidates = new ArrayList<>();
	Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);
	for (Method candidate : rawCandidates) {
	if ((!isStatic || isStaticCandidate(candidate, factoryClass)) && mbd.isFactoryMethod(candidate)) {
	candidates.add(candidate);
	}
	}
	}

At below line, it gets all candidates to generate that bean but ignore the methods in super class if there already found a method with the same signature, so it'll only keeps class com.ai.demo.configtest.BeanOverridingChild.

spring-framework/spring-beans/src/main/java/org/springframework/beans/factory/support/ConstructorResolver.java

Line 468 in c04290e

Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);

But the mbd.isFactoryMethod at below have to verify if the bean name is equal to the one from the method, and it fails.

spring-framework/spring-beans/src/main/java/org/springframework/beans/factory/support/ConstructorResolver.java

Line 470 in c04290e

if ((!isStatic || isStaticCandidate(candidate, factoryClass)) && mbd.isFactoryMethod(candidate)) {

Then after various checks it decides to throw an BeanCreationException.

spring-framework/spring-beans/src/main/java/org/springframework/beans/factory/support/ConstructorResolver.java

Line 611 in c04290e

throw new BeanCreationException(mbd.getResourceDescription(), beanName,

---

That mbd object in code mbd.getResolvedFactoryMethod() is getting factoryMethodToIntrospect field inside itself, the difference is from

spring-framework/spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassBeanDefinitionReader.java

Lines 232 to 234 in c04290e

	if (metadata instanceof StandardMethodMetadata sam) {
	beanDef.setResolvedFactoryMethod(sam.getIntrospectedMethod());
	}

here can have SimpleAnnotationMetadata when use ScanComponent and StandardAnnotationComponent when use Import, that explains everything.

---

I personally think it is a problem and that only keeping bean in sub class is optimal. but on the opposite side I also think this can rarely become a realistic situation, so if it worthy to change the code takes me into dilemma.

[snicoll]

Duplicate of #28286