@Autowired,@Inject,@Resource

刺骨的言语ヽ痛彻心扉 2022-06-05 08:45 169阅读 0赞

<table> 
 <thead> 
  <tr> 
   <th>Annotation</th> 
   <th>Package</th> 
   <th>Source</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>@Resource</td> 
   <td>javax.annotation</td> 
   <td>Java(JSR-250)</td> 
  </tr> 
  <tr> 
   <td>@Inject</td> 
   <td>javax.inject</td> 
   <td>Java(JSR-330)</td> 
  </tr> 
  <tr> 
   <td>@Qualifier</td> 
   <td>javax.inject</td> 
   <td>Java</td> 
  </tr> 
  <tr> 
   <td>@Autowired</td> 
   <td>org.springframework.bean.factory</td> 
   <td>Spring</td> 
  </tr> 
 </tbody> 
</table>

> The @Autowired and @Inject annotation behave identically. Both of these annotations use the **AutowiredAnnotationBeanPostProcessor** to inject dependencies. @Autowired and @Inject can be used interchangeable to inject Spring beans. However the @Resource annotation uses the **CommonAnnotationBeanPostProcessor** to inject dependencies.

@Autowired和@Inject注释的行为完全相同，均使用用**AutowiredAnnotationBeanPostProcessor**注入依赖项。而@Resource注释使用**CommonAnnotationBeanPostProcessor**进行注入，两者注释策略如下：

#### @Autowired and @Inject ####

*  Matches by Type
 *  Restricts by Qualifiers
 *  Matches by Name

#### @Resource ####

*  Matches by Name
 *  Matches by Type
 *  Restricts by Qualifiers (ignored if match is found by name)

@Autowired默认按类型装配，默认情况下必须要求依赖对象必须存在，如果要允许null 值，可以设置它的required属性为false，如：@Autowired(required=false) ，如果我们想使用名称装配可以结合@Qualifier注解进行使用，如下：

@Autowired
        @Qualifier("***")     
        private Bean bean;

@Resource默认安照名称进行装配，名称可以通过name属性进行指定， 如果没有指定name属性，当注解写在字段上时，默认取字段名进行按照名称查找，如果注解写在setter方法上默认取属性名进行装配。 当找不到与名称匹配的bean时才按照类型进行装配。name属性一旦指定，就只会按照名称进行装配。

>  *  Good practice would be to use @Inject instead of @Autowired because it is not Spring-specific and is part of the JSR-330 standard  
>       
>     
>  *  Another good practice would be to put the @Inject / @Autowired on a constructor instead of a method. If you put it on a constructor, you can validate that the injected beans are not null and fail fast when you try to start the application and avoid a NullPointerException when you need to actually use the bean.

*  好的做法是使用@Inject（非Spring特有的，而是JSR-330标准的一部分）而不是@Autowired。
 *  另一个好的实践是将[@Inject/@Autowired][Inject_Autowired]注解在构造函数而不是方法上。这样可以快速验证注入Bean是否非空(程序启动时快速抛错)，避免在需要实际使用bean时出现NullPointerException异常。

[https://blogs.sourceallies.com/2011/08/spring-injection-with-resource-and-autowired/][https_blogs.sourceallies.com_2011_08_spring-injection-with-resource-and-autowired]

[https://stackoverflow.com/questions/19414734/understanding-spring-autowired-usage][https_stackoverflow.com_questions_19414734_understanding-spring-autowired-usage]

[Inject_Autowired]: https://stackoverflow.com/questions/20485059/spring-boot-how-can-i-set-the-logging-level-with-application-properties
[https_blogs.sourceallies.com_2011_08_spring-injection-with-resource-and-autowired]: https://blogs.sourceallies.com/2011/08/spring-injection-with-resource-and-autowired/
[https_stackoverflow.com_questions_19414734_understanding-spring-autowired-usage]: https://stackoverflow.com/questions/19414734/understanding-spring-autowired-usage

@Autowired,@Inject,@Resource

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