自动装配Spring超类 [英] Autowiring Spring superclass

问题描述

为什么Spring在自动装配过程中会自动选择超类类型?

Why does Spring automatically choose the superclass types during autowiring?

例如，如果我有

@Component
public class Foo {}

@Component
public class Bar extends Foo {}

有人自动接线

@Autowired
private Foo foo;

Spring为什么总是选择父类型Foo?这不应该是"模糊"映射(并导致Spring引发错误)吗?

How come Spring always chooses the supertype Foo? Shouldn't this be an "ambiguous" mapping (and cause Spring to throw an error)?

从技术上讲，您不是有两个 Foo个候选人吗? (例如，当从Foo中删除@Component时，Bar被自动选择)

Don't you technically have two Foo candidates? (e.g., Bar gets automatically picked when @Component is removed from Foo...)

推荐答案

这可能是因为自动装配是通过名称而不是类型完成的.如果我使用xml这样设置Bean:

That might be because the autowiring is done by name, not type. If I setup my bean using xml like this:

<bean id="foo1" class="Foo"/>
<bean id="foo2" class="Bar"/>

并尝试按类型自动接线:

And attempt to autowire by type:

@Autowired private Foo aFoo;

我知道

org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [Foo]

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