I find some answer: https://stackoverflow.com/a/21218921/2754014 about Dependency Injection. There isn't any annotation like @Autowired
, @Inject
or @Resource
. let's assume that there isn't any XML configuration for this example TwoInjectionStyles
bean (except simple <context:component-scan base-package="com.example" />
.
Is it correct to inject without specify annotation?
From Spring 4.3 annotations are not required for constructor injection.
public class MovieRecommender {
private CustomerPreferenceDao customerPreferenceDao;
private MovieCatalog movieCatalog;
//@Autowired - no longer necessary
public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
this.customerPreferenceDao = customerPreferenceDao;
}
@Autowired
public setMovieCatalog(MovieCatalog movieCatalog) {
this.movieCatalog = movieCatalog;
}
}
But you still need @Autowired
for setter injection. I checked a moment ago with Spring Boot 1.5.7
(using Spring 4.3.11
) and when I removed @Autowired
then bean was not injected.
Yes, example is correct (starting from Spring 4.3 release). According to the documentation ( this for ex), if a bean has single constructor, @Autowired
annotation can be omitted.
But there are several nuances:
1. When single constructor is present and setter is marked with @Autowired
annotation, than both constructor & setter injection will be performed one after another:
@Component
public class TwoInjectionStyles {
private Foo foo;
public TwoInjectionStyles(Foo f) {
this.foo = f; //Called firstly
}
@Autowired
public void setFoo(Foo f) {
this.foo = f; //Called secondly
}
}
2. At the other hand, if there is no @Autowire
at all (as in your example ), than f
object will be injected once via constructor, and setter can be used in it's common way without any injections.
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