问题描述
所以，如果我理解正确的话，如果有多个候选者，两者都是确定哪个bean自动装配的方法。那究竟是什么区别呢？
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
阅读作为默认。
Read @Primary as the "default".
如果bean有 @Autowired 没有任何 @Qualifier ，并且存在多个类型的bean，将选择标记为 @Primary 的候选bean，即它是默认选择当没有其他信息可用时，即 @Qualifier 缺失时。
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.
一个好的用例是你最初的只有一个类型的bean，所以没有任何代码使用 @Qualifier 。然后当你添加另一个bean时，你还要将 @Qualifier 添加到旧bean和新bean中，所以任何 @Autowired 可以选择它想要的那个。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bean中 @Autowired 。可以这么说它们是grand来。
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 也是好的，例如95％的 @Autowired 想要一个特定的bean。这样，只有想要其他bean的 @Autowired 需要指定 @Qualifier 。这样，您拥有所有自动装配的主bean，而 @Qualifier 仅用于请求备用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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