@Resource vs @Autowired vs @Inject

概述

在 spring 中 @Resource、@Autowired 和 @Inject 都可以用来注入 bean，那么他们有什么区别呢？

从最终结果来看

如果仅仅从结果来看，他们几乎没区别，只不过他们查找 Bean 的顺序不同。

@Autowired 和 @Inject 查找 Bean 的顺序

• 通过类型匹配 bean
• 应用 Qualifiers 限制
• 通过名称匹配

@Resource 查找 Bean 的顺序

• 通过名称匹配
• 通过类型匹配 bean
• 应用 Qualifiers 限制

注：@Autowired 使用 AutowiredAnnotationBeanPostProcessor 来注入 Bean，@Resource 使用 CommonAnnotationBeanPostProcessor 来注入 Bean。

从语义来看

stackoverflow 上对此作了比较好的回答：resource-vs-autowired

Both @Autowired (or @Inject) and @Resource work equally well. But there is a conceptual difference or a difference in the meaning:

@Resource means get me a known resource by name. The name is extracted from the name of the annotated setter or field, or it is taken from the name-Parameter.
@Inject or @Autowired try to wire in a suitable other component by type.
So, basically these are two quite distinct concepts. Unfortunately the Spring-Implementation of @Resource has a built-in fallback, which kicks in when resolution by-name fails. In this case, it falls back to the @Autowired-kind resolution by-type. While this fallback is convenient, IMHO it causes a lot of confusion, because people are unaware of the conceptual difference and tend to use @Resource for type-based autowiring.

意思是 @Resource 的本意是为了根据名称来匹配 Bean，但是不幸的是 spring 的实现却是先按照名称，如果按照名称找不到，则根据类型匹配；@Autowired 本意则是根据类型匹配。