How @Fallback Redefines Spring Bean Selection in 6.2

1. Introduction

When multiple beans of the same type exist in the Spring container, the @Primary annotation is used to indicate which bean should be injected by default.

<code>public interface CommonDAO {}
public class UserDAO implements CommonDAO {}
public class PersonDAO implements CommonDAO {}
public class CommonService {
    private CommonDAO dao;
    public CommonService(CommonDAO dao) { this.dao = dao; }
}

@Configuration
public class Module1Config {
    @Bean
    public UserDAO userDAO() { return new UserDAO(); }
    @Bean
    public CommonService commonService(CommonDAO dao) { return new CommonService(dao); }
}

@Configuration
public class Module2Config {
    @Bean
    @Primary
    public PersonDAO personDAO() { return new PersonDAO(); }
}
</code>

Other ways besides @Primary exist; see related articles for alternatives.

2. New Feature: @Fallback

Spring 6.2 introduces the @Fallback annotation, which marks a bean as a fallback candidate and serves as an alternative to @Primary. If several candidates are marked as fallback, the remaining beans are selected. The fallback works only when a single injection point has multiple candidates; for collections, all matching beans are included.

<code>@Configuration
public class AppConfig {
    @Bean
    public UserDAO userDAO() { return new UserDAO(); }
    @Bean
    @Fallback
    public PersonDAO personDAO() { return new PersonDAO(); }
    @Bean
    public CommonService commonService(CommonDAO dao) { return new CommonService(dao); }
}
</code>

In this example, CommonService receives UserDAO ; if UserDAO is absent, the PersonDAO marked with @Fallback will be injected.

If multiple beans are marked @Fallback without a default, injection for a single point will fail.

<code>@Bean
@Fallback
public UserDAO userDAO() { return new UserDAO(); }

@Bean
@Fallback
public PersonDAO personDAO() { return new PersonDAO(); }
</code>

When one bean is @Fallback and another is @Primary, @Primary takes precedence.

<code>@Fallback
public UserDAO userDAO() { }

@Primary
public PersonDAO personDAO() { }
</code>

Bean Selection Order in Spring 6.2

@Primary (searched first, then non‑@Fallback)

Match by field or parameter name

@Qualifier (specified value name)

@Priority

Directly registered dependencies (static registration)

Bean Selection Order before Spring 6.2

@Primary

@Priority

Directly registered dependencies

Direct registration can be done manually, for example:

<code>// manual BeanFactory creation
DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
beanFactory.registerResolvableDependency(CommonDAO.class, TeacherDAO.class);
</code>

That concludes the article.