ConfigurationProperties constructor @Autowired detection fails for proxy classes

Spring Boot 3. See minimized example project: https://github.com/matthenry87/configprops-bug

    @Configuration
    @ConfigurationProperties(prefix = "foo")
    static class ConfigPropertiesConfigBean {

        private final Environment environment;

        private String bar;

        public ConfigPropertiesConfigBean(Environment environment) {

            this.environment = environment;
        }

        public String getBar() {

            return bar;
        }

        public void setBar(String bar) {

            this.bar = bar;
        }

    }

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'configpropsBugApplication.ConfigPropertiesConfigBean' defined in file [C:\workspace\configprops-bug\target\classes\org\matthenry87\configpropsbug\ConfigpropsBugApplication$ConfigPropertiesConfigBean.class]: Cannot bind @ConfigurationProperties for bean 'configpropsBugApplication.ConfigPropertiesConfigBean'. Ensure that @ConstructorBinding has not been applied to regular bean
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:606) ~[spring-beans-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:521) ~[spring-beans-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:326) ~[spring-beans-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:324) ~[spring-beans-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:200) ~[spring-beans-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:931) ~[spring-beans-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:916) ~[spring-context-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:584) ~[spring-context-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:730) ~[spring-boot-3.0.0-RC1.jar:3.0.0-RC1]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:432) ~[spring-boot-3.0.0-RC1.jar:3.0.0-RC1]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:308) ~[spring-boot-3.0.0-RC1.jar:3.0.0-RC1]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1302) ~[spring-boot-3.0.0-RC1.jar:3.0.0-RC1]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1291) ~[spring-boot-3.0.0-RC1.jar:3.0.0-RC1]
	at org.matthenry87.configpropsbug.ConfigpropsBugApplication.main(ConfigpropsBugApplication.java:14) ~[classes/:na]
Caused by: java.lang.IllegalStateException: Cannot bind @ConfigurationProperties for bean 'configpropsBugApplication.ConfigPropertiesConfigBean'. Ensure that @ConstructorBinding has not been applied to regular bean
	at org.springframework.util.Assert.state(Assert.java:76) ~[spring-core-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.bind(ConfigurationPropertiesBindingPostProcessor.java:86) ~[spring-boot-3.0.0-RC1.jar:3.0.0-RC1]
	at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.postProcessBeforeInitialization(ConfigurationPropertiesBindingPostProcessor.java:78) ~[spring-boot-3.0.0-RC1.jar:3.0.0-RC1]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:420) ~[spring-beans-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1745) ~[spring-beans-6.0.0-RC2.jar:6.0.0-RC2]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:599) ~[spring-beans-6.0.0-RC2.jar:6.0.0-RC2]
	... 14 common frames omitted

[wilkinsona]

Is the recommendation just for separation of concerns? Or are there other negative consequences?

It’s largely for separation of concerns. You also need to consider that @Configuration is a specialisation of @Component so your configuration property beans will now be picked up by component scanning. That may not be what you want.

In your experience is it more common that the @ConfigurationProperties class/bean is injected into the bean that needs it rather than passing the fields to it inside of the @Bean method?

Yes. In Boot’s own codebase, our @ConfigurationProperties classes are separate from our @Configuration classes with the former being injected into the latter as needed. The documentation also does not mix @Configuration and @ConfigurationProperties on the same class. From what I’ve seen, most people have followed this pattern in their own code.

[philwebb]

@wilkinsona I’ve refined it a bit and pushed. I think we should consider all constructors when looking for @Autowired, including those on user-classes if it’s a proxy.