注释类型 Primary

@Target({TYPE,METHOD})
@Retention(RUNTIME)
@Inherited
@Documented
public @interface Primary

Indicates that a bean should be given preference when multiple candidates are qualified to autowire a single-valued dependency. If exactly one 'primary' bean exists among the candidates, it will be the autowired value.

This annotation is semantically equivalent to the <bean> element's primary attribute in Spring XML.

May be used on any class directly or indirectly annotated with @Component or on methods annotated with @Bean.

Example

 @Component
 public class FooService {

     private FooRepository fooRepository;

     @Autowired
     public FooService(FooRepository fooRepository) {
         this.fooRepository = fooRepository;
     }
 }

 @Component
 public class JdbcFooRepository extends FooRepository {

     public JdbcFooRepository(DataSource dataSource) {
         // ...
     }
 }

 @Primary
 @Component
 public class HibernateFooRepository extends FooRepository {

     public HibernateFooRepository(SessionFactory sessionFactory) {
         // ...
     }
 }
 

Because HibernateFooRepository is marked with @Primary, it will be injected preferentially over the jdbc-based variant assuming both are present as beans within the same Spring application context, which is often the case when component-scanning is applied liberally.

Note that using @Primary at the class level has no effect unless component-scanning is being used. If a @Primary-annotated class is declared via XML, @Primary annotation metadata is ignored, and <bean primary="true|false"/> is respected instead.