@Component
@Service
@Repository
@Controller
@RestController
@Configuration // @Configuration 也是 @Component

@Service
public class UserService {
    public void save() { ... }
}

@Configuration
public class RedisConfig {
    
    @Bean
    public RedisTemplate<String, Object> redisTemplate(RedisConnectionFactory factory) {
        RedisTemplate<String, Object> template = new RedisTemplate<>();
        template.setConnectionFactory(factory);
        return template;
    }
}

app:
  title: MyApp
  version: 1.0.0

@Component
@ConfigurationProperties(prefix = "app")
public class AppProperties {
    private String title;
    private String version;
    // getter/setter
}

@Configuration
@EnableConfigurationProperties(AppProperties.class)
public class AppConfig {
}

@Import(DatabaseConfig.class)
@SpringBootApplication
public class Application { }

@Import(UserService.class)

@Import(MyImportSelector.class)
public class Application { }

public class MyImportSelector implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{MyService.class.getName()};
    }
}

public class MyFactoryBean implements FactoryBean<MyService> {

    @Override
    public MyService getObject() throws Exception {
        MyService service = new MyService();
        service.init(); // 復(fù)雜初始化
        return service;
    }

    @Override
    public Class<?> getObjectType() {
        return MyService.class;
    }

    @Override
    public boolean isSingleton() {
        return true;
    }
}

@Component
public class MyFactoryBean { } // Spring 會調(diào)用 getObject() 創(chuàng)建 MyService Bean

@Bean
@ConditionalOnMissingBean(DataSource.class)
public DataSource dataSource() {
    return new HikariDataSource();
}

@Component
public class DynamicBeanRegistrar implements BeanDefinitionRegistryPostProcessor {

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(UserService.class);
        AbstractBeanDefinition definition = builder.getBeanDefinition();
        registry.registerBeanDefinition("userService", definition);
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        // do nothing
    }
}

<bean id="userService" class="com.example.UserService"/>

ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");