So, I have the following application:
@SpringBootApplication
public class AutonullApplication {
public static void main(String[] args) {
SpringApplication.run(AutonullApplication.class, args);
}
@Bean
First first() {
return null;
}
public class First {
}
@Service
public class Second {
private final First first;
public Second(First first) {
this.first = first;
}
@PostConstruct
public void print() {
System.out.println("First = " + first);
}
}
}
which tries to inject a bean of type First into a service of type Second. But the bean has a value of null. This code works fine in Spring Boot 1.5.10 (and so Spring 4), but fails in Spring Boot 2.0 (and Spring 5):
Description:
Parameter 1 of constructor in eu.plumbr.autonull.AutonullApplication$Second required a bean of type 'eu.plumbr.autonull.AutonullApplication$First' that could not be found.
Is anybody aware of any mention of such change in the official documentation?
Yes, this is a breaking change in Spring Framework 5. Arguably, such setup is weird and we wanted to tighten those rules a little bit.
If you request to inject First and you provide null, then it's more consistent to consider that bean isn't provided. You can then query the context for the presence of First. @spencergibb already explained how you can use Optional, or you can use ObjectProvider<First> as an injection point:
@Service
public class Second {
private final First first;
public Second(ObjectProvider<First> first) {
this.first = first.getIfAvailable(); // return null
}
}