@Autowired,@Inject,@Resource，@autowired@inject

@Autowired,@Inject,@Resource，@autowired@inject

Annotation	Package	Source
@Resource	javax.annotation	Java(JSR-250)
@Inject	javax.inject	Java(JSR-330)
@Qualifier	javax.inject	Java
@Autowired	org.springframework.bean.factory	Spring

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://stackoverflow.com/questions/19414734/understanding-spring-autowired-usage