Spring inject without autowire annotation

Question

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?

Krzysztof Atłasik · Accepted Answer · 2020-05-05T08:36:19.047

26

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.

edited May 05 '20 at 08:36

answered Oct 02 '17 at 12:11

Krzysztof Atłasik

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So this anwser https://stackoverflow.com/a/21218921/2754014 is not correct? – kuba44 Oct 02 '17 at 12:13
2

Unless I missed something, won't work. So your're right, without any xml configuration this answer is incorrect. – Krzysztof Atłasik Oct 02 '17 at 15:08
1

This official example is kind of misleading me. I thought setter injection would work without @Autowired if it has a no-arg constructor. https://docs.spring.io/spring/docs/4.3.x/spring-framework-reference/htmlsingle/#beans-setter-injection – Anderson Aug 24 '20 at 08:41

Alex Saunin · Answer 2 · 2017-10-02T21:03:27.137

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.

Spring inject without autowire annotation

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