Postconstruct is called twice for programmaticaly created bean

[loicmathieu]

Expected Behavior

When a bean is created manually then registed via regiserSingleton, if it has a method annoted with @PostConstruct this method must be called once.

Actual Behaviour

Take as example the following bean:

@Singleton
public class MyBean {

    @PostConstruct
    void init() {
        System.out.println("MyBean init " + this);
    }

    public String hello() {
        return "hello";
    }
}

When constructed then registered programmatically like that:

public class Application {

    public static void main(String[] args) {
        ApplicationContext applicationContext = Micronaut.run(Application.class, args);
        MyBean bean = applicationContext.createBean(MyBean.class);
        applicationContext.registerSingleton(bean);

        System.out.println(bean.hello());
    }
}

The postconstruct method is called twice.

Steps To Reproduce

double-postconstruct.zip

Environment Information

• OS: Linux 6.11.0-19-generic replace grails-shello with micronaut-shell #19-Ubuntu SMP PREEMPT_DYNAMIC Wed Feb 12 21:43:43 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
• Java: openjdk version "21.0.5" 2024-10-15 LTS

Example Application

No response

Version

4.7.6

[graemerocher]

I don't think this is a supported pattern (ie. calling createBean and then registerSingleton). Changing this behaviour my break existing users as well.

[loicmathieu]

The documentation of createBean says that the singleton is not registered so I had to register it manually if I want to be able to inject it.

I create beans conditionally, in a command, with parameters passed as command line options so I had to use createBean.

Maybe a solution would be to create the bean with new, manually do injection (applicationContext.init()) then register it?

[graemerocher]

createBean is normally not used in combination with @Singleton because a singleton is... well singleton, there is only one