使用 @Primary 或 @Fallback 对基于注释的自动连接进行微调

Hunyuan 7b 中英对照 Fine-tuning Annotation-based Autowiring with @Primary or @Fallback Fine-tuning Annotation-based Autowiring with @Primary or @Fallback

由于类型自动配置可能会导致多个候选Bean，因此通常需要对选择过程有更多的控制。实现这一目标的一种方法是使用Spring的@Primary注解。@Primary表示当有多个Bean可以作为单个值依赖的自动配置候选时，应优先选择某个特定的Bean。如果在候选Bean中恰好存在一个唯一的@Primary Bean，那么它就会成为自动配置的值。

考虑以下配置，该配置将 firstMovieCatalog 定义为主要的 MovieCatalog：

Java

@Configuration
public class MovieConfiguration {

	@Bean
	@Primary
	public MovieCatalog firstMovieCatalog() { ... }

	@Bean
	public MovieCatalog secondMovieCatalog() { ... }

	// ...
}

Kotlin

@Configuration
class MovieConfiguration {

	@Bean
	@Primary
	fun firstMovieCatalog(): MovieCatalog { ... }

	@Bean
	fun secondMovieCatalog(): MovieCatalog { ... }

	// ...
}

或者，从版本6.2开始，有一个@Fallback注解，用于标记除了常规bean之外的其他需要注入的bean。如果只剩下一个常规bean，那么它实际上也会被视为主要bean（primary）。

Java

@Configuration
public class MovieConfiguration {

	@Bean
	public MovieCatalog firstMovieCatalog() { ... }

	@Bean
	@Fallback
	public MovieCatalog secondMovieCatalog() { ... }

	// ...
}

Kotlin

@Configuration
class MovieConfiguration {

	@Bean
	fun firstMovieCatalog(): MovieCatalog { ... }

	@Bean
	@Fallback
	fun secondMovieCatalog(): MovieCatalog { ... }

	// ...
}

使用上述配置的两种变体，以下的 MovieRecommender 都会自动与 firstMovieCatalog 连接（即实现自动配置）：

Java

public class MovieRecommender {

	@Autowired
	private MovieCatalog movieCatalog;

	// ...
}

Kotlin

class MovieRecommender {

	@Autowired
	private lateinit var movieCatalog: MovieCatalog

	// ...
}

相应的bean定义如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
		https://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/context
		https://www.springframework.org/schema/context/spring-context.xsd">

	<context:annotation-config/>

	<bean class="example.SimpleMovieCatalog" primary="true">
		<!-- inject any dependencies required by this bean -->
	</bean>

	<bean class="example.SimpleMovieCatalog">
		<!-- inject any dependencies required by this bean -->
	</bean>

	<bean id="movieRecommender" class="example.MovieRecommender"/>

</beans>