Kotlin BeanFactory.getBean extension fails with nested generic in context

[ianbrandt]

With 6.1.0-RC1 (and likely prior), the following test of the BeanFactory.getBean extension fails, presumably due to erasure:

@SpringBootTest
internal class SpringGetBeanNestedGenericIT {

	@Configuration
	class TestConfig {

		@Bean
		fun listOfString(): List<String> =
			listOf("Testing")

		@Bean
		fun listOfListOfString(): List<List<String>> =
			listOf(listOf("Testing"))
	}

	@Test
	fun `test getBean with nested generic`(
		applicationContext: ApplicationContext
	) {
		assertThatNoException().isThrownBy {

			applicationContext.getBean<List<String>>()
		}
	}
}

Error message showing the listOfString and listOfListOfString beans being seen as the same type after erasure:

java.lang.AssertionError: 
Expecting code not to raise a throwable but caught
  "org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'java.util.List' available: expected single matching bean but found 2: listOfString,listOfListOfString
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:1310)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveBean(DefaultListableBeanFactory.java:484)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:339)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:332)
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1192)
	at org.sdkotlin.springdemo.SpringGetBeanNestedGenericIT.test_getBean_with_nested_generic$lambda$0(SpringGetBeanNestedGenericIT.kt:37)
	at org.assertj.core.api.ThrowableAssert.catchThrowable(ThrowableAssert.java:63)
	at org.assertj.core.api.NotThrownAssert.isThrownBy(NotThrownAssert.java:43)
	at org.sdkotlin.springdemo.SpringGetBeanNestedGenericIT.test getBean with nested generic(SpringGetBeanNestedGenericIT.kt:30)

If I remove the listOfListOfString bean from the configuration, the test passes.

I can inject both beans just fine, i.e. the following passes:

@Test
fun `test listOfString is injected`(
	@Autowired
	listOfString: List<String>
) {
	assertThat(listOfString).isEqualTo(LIST_OF_STRING)
}

@Test
fun `test listOfListOfString is injected`(
	@Autowired
	listOfListOfString: List<List<String>>
) {
	assertThat(listOfListOfString).isEqualTo(LIST_OF_LIST_OF_STRING)
}

I notice the BeanFactory.getBeanProvider extension uses the super type token approach. Perhaps this could be used as well for getBean to address this issue:

inline fun <reified T : Any> BeanFactory.getBean(): T =
	getBeanProvider<T>(ResolvableType.forType((object : ParameterizedTypeReference<T>() {}).type)).`object`

If I import that version of the extension instead, the test passes with the listOfListOfString bean in the configuration.

[ianbrandt]

Added #31444 to request ParameterizedTypeReference overloads to the Java BeanFactory.getBean methods, which would presumably streamline the implementation of the Kotlin extensions.

[sdeleuze]

You can get the behavior you want with applicationContext.getBeanProvider<List<String>>().getObject() or getIfAvailable() since we are leveraging the underlying ResolvableType based capabilities. That said, we could maybe potentially leverage that instead of getBean(T::class.java) for the implementation of the inline fun <reified T : Any> BeanFactory.getBean(): T Kotlin extension. I will give it more thoughts and let you know.

[ianbrandt]

Thanks for the fix, @sdeleuze!