Spring Framework (24 Part Series)

1 Spring Configuration
2 External Properties in Spring
… 20 more parts…
3 Profiles in Spring
4 Spring Expression Language (SpEL)
5 How Spring implements Singleton Beans
6 Converting explicit into implicit configuration in Spring
7 Autowiring in Spring
8 Lazy Beans in Spring
9 @PostConstruct and @PreDestroy in Spring
10 Stereotype and Meta Annotations in Spring
11 Spring’s FactoryBean Interface
12 The Spring Bean Lifecycle
13 Spring AOP
14 Caching in Spring
15 Spring JDBC
16 Spring Transaction Management
17 JPA with Spring
18 JPA with Spring Boot
19 Spring Web MVC
20 Spring Boot for war
21 Spring MVC REST
22 Reactive Spring Applications
23 Spring Security
24 Spring Injection Types

Constructor Injection

    @Autowired
    public AppServiceImpl(AppRepository appRepository) {
        this.appRepository = appRepository;
    }

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Method Injection

    @Autowired
    public setRepository(AppRepository appRepository) {
        this.appRepository = appRepository;
    }

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Field Injection

Not recommended. Hard to unit test.

    @Autowired
    private AppRepository appRepository;

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Optional dependencies

Only inject if dependency exists:

    @Autowired(required=false)
    AppService appService;

    public void method() {
      if(appService != null) {
        ...
      }
    }

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Using Optional:

    @Autowired
    Optional<AppService> appService;

    public void method() {
      appService.ifPresent(s -> {
        ...
      });
    }

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Qualifier Annotation

When component names are not specified, they are auto-generated. When specified, they allow disambiguation if more than one bean class implements the same interface.

@Component
public class AppServiceImpl implements AppService {
    @Autowired
    public AppServiceImpl(@Qualifier("jdbcRepository") AppRepository appRepository) {
        this.appRepository = appRepository;
    }
}

@Component("jdbcRepository")
public class JdbcRepositoryImpl implements AppRepository {
    ...
}

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Spring Framework (24 Part Series)

1 Spring Configuration
2 External Properties in Spring
… 20 more parts…
3 Profiles in Spring
4 Spring Expression Language (SpEL)
5 How Spring implements Singleton Beans
6 Converting explicit into implicit configuration in Spring
7 Autowiring in Spring
8 Lazy Beans in Spring
9 @PostConstruct and @PreDestroy in Spring
10 Stereotype and Meta Annotations in Spring
11 Spring’s FactoryBean Interface
12 The Spring Bean Lifecycle
13 Spring AOP
14 Caching in Spring
15 Spring JDBC
16 Spring Transaction Management
17 JPA with Spring
18 JPA with Spring Boot
19 Spring Web MVC
20 Spring Boot for war
21 Spring MVC REST
22 Reactive Spring Applications
23 Spring Security
24 Spring Injection Types

原文链接：Autowiring in Spring