parameters of @Bean annotated method

Question

In the following code, a MvcRequestMatcher.Builder bean is registered with application context.

@Bean
MvcRequestMatcher.Builder mvc(HandlerMappingIntrospector introspector) {                        
    return new MvcRequestMatcher.Builder(introspector);
}

the method takes a introspector parameter which itself is autowired bean. My question is since it's not a constructor nor a setter, and there is no @Autowired annotation, what kind of injection is it?

Answer 1

It is called method injection. you can use it in configuring beans in @Configuration class, it gives more flexibility and makes it clear which dependencies are needed for specific methods. also you can use it when a dependency is not always required and should only be injected under certain conditions like this:

@Bean
public MyBean myBean(@Autowired(required = false) OptionalDependency optionalDependency) {
    if (optionalDependency != null) {
        // Use the optional dependency
    } else {
        // Handle the absence of the optional dependency
    }
    return new MyBean(optionalDependency);
}