@Primary 与 @Autowired 与 @Qualifier 注释的区别 [英] Difference between @Primary vs @Autowired with @Qualifier annotations

问题描述

所以，如果我理解正确的话，如果有多个候选者，两者都是确定要自动装配哪个 bean 的方法.那么究竟有什么区别呢?

So, if I understood correctly, both are the way to determine which bean to autowire if there are multiple candidates. So what exactly is the difference?

推荐答案

阅读 @Primary 作为默认".

Read @Primary as the "default".

如果一个bean有@Autowired 没有任何@Qualifier，并且存在多个该类型的bean，则标记为的候选bean@Primary 将被选中，即当没有其他信息可用时，即当 @Qualifier 缺失时，它是默认选择.

If a bean has @Autowired without any @Qualifier, and multiple beans of the type exist, the candidate bean marked @Primary will be chosen, i.e. it is the default selection when no other information is available, i.e. when @Qualifier is missing.

一个很好的用例是，最初您只有一个该类型的 bean，所以没有使用 @Qualifier 的代码.当您添加另一个 bean 时，您还将 @Qualifier 添加到旧 bean 和新 bean，因此任何 @Autowired 都可以选择它想要的.通过将 @Primary 添加到旧的原始 bean，您不必将 @Qualifier 添加到所有现有的 @Autowired.可以这么说，他们是祖父".

A good use case is that initially you only had one bean of the type, so none of the code used @Qualifier. When you then add another bean, you then also add @Qualifier to both the old and the new bean, so any @Autowired can choose which one it wants. By also adding @Primary to the old original bean, you don't have to add @Qualifier to all the existing @Autowired. They are "grandfathered" in, so to speak.

@Primary 也很好，例如95% 的 @Autowired 想要一个特定的 bean.这样，只有需要其他 bean 的 @Autowired 需要指定 @Qualifier.这样，您就有了所有自动装配所需的主要 bean，而 @Qualifier 仅用于请求替代"bean.

@Primary is also good if e.g. 95% of @Autowired wants a particular bean. That way, only the @Autowired that wants the other bean(s) need to specify @Qualifier. That way, you have primary beans that all autowired wants, and @Qualifier is only used to request an "alternate" bean.

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