What bean injection methods do you know in Spring?

In the Spring Framework, there are several main ways to inject beans:

1. Constructor Injection — dependencies are passed through the class constructor parameters. This is the preferred method as it allows creating immutable objects and simplifies testing.

@Component
public class Service {
    private final Repository repo;

    @Autowired
    public Service(Repository repo) {
        this.repo = repo;
    }
}

2. Setter Injection — dependencies are set through setter methods. It allows changing dependencies after object creation.

@Component
public class Service {
    private Repository repo;

    @Autowired
    public void setRepository(Repository repo) {
        this.repo = repo;
    }
}

3. Field Injection — dependencies are injected directly into class fields using the @Autowired annotation. It is less preferred due to testing complexity and encapsulation issues.

@Component
public class Service {
    @Autowired
    private Repository repo;
}

Each method has its pros and cons, but constructor injection is considered the cleanest and most recommended practice.