Is there any default bean initialization order implicitly in a Spring Boot application? I came across this question in one of my Spring Boot applications when trying to use @ConditionalOnBean annotation.
At first, I thought that Spring does not guarantee any Bean creation order when it's loading beans in @Configuration class or when it's doing component-scan to auto register @Component/@Service/.. classes.
But later, I noticed that in the Spring documentation, it mentions that,
Auto-configuration classes are guaranteed to load after any user-defined bean definitions have been added.
This somehow makes me confused,
1. What counts user defined bean and what counts auto-configuration classes? Specifically, is there any loading order between @Bean in @Configuration class and @Component/@Service directly on class level.
2. If a bean A needs dependency injection of bean B, will B always be initialized first?
3. If @Import is used for configuration aggregation in a Spring Boot application, will beans defined in the imported configuration class being initialized before component-scanned bean registration.
@Component
public class A {}
@Component
public class B {
@Autowired
private A a;
}
@Configuration
public class externalConfig {
@Bean
public C c() {
return new C();
}
}
@SpringBootApplication
@Import(externalConfig.class)
public class testApplication {
@Bean
public D d() {
return new D();
}
}
When comes to the above code example, my question becomes the following.
1. Without @Import, will C or D always be initialized before A and B?
2. Will B always be initialized before A?
3. With @Import, will C always be initialized first, like even before D?
