sping mvc 使用@Value注解为controller注入值

spring mvc 里有两个配置文件，
第一个，为spring的service和dao进行配置的配置文件，对应springMVC的父context applicationContext

<!--applicationContext.xml -->
<context:property-placeholder ignore-unresolvable="true"
			location="classpath*:/application.properties" />	

第二个,为spring MVC的controller进行配置的配置文件，对应springMVC里的子context webapplicationContext，该webapplicationContext继承自父context，所以可以访问父context的bean。

<!--spring-mvc.xml -->
<!-- 自动扫描且只扫描@Controller -->
	<context:component-scan base-package="com.xxxx.web" use-default-filters="false">
		<context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
		<context:include-filter type="annotation" expression="org.springframework.web.bind.annotation.ControllerAdvice"/>
	</context:component-scan>

service 里可以直接值使用@Value("${someprop}")的方式直接拿到属性值，

对于controller来说，就没有那么简单了，不能直接使用@Value("${someprop}")注入属性值，参阅外国达人的分析
Spring @Value annotation in @Controller class not evaluating to value inside properties file

引用

It seems that the question has been already asked Spring 3.0.5 doesn't evaluate @Value annotation from properties

The difference between web app root and servlet application contexts is one of the top sources of confusion in Spring, see difference between applicationContext and spring-servlet.xml in spring

From @Value javadoc :

    Note that actual processing of the @Value annotation is performed by a BeanPostProcessor

From Spring documentation:

    BeanPostProcessor interfaces are scoped per-container. This is only relevant if you are using container hierarchies. If you define a BeanPostProcessor in one container, it will only do its work on the beans in that container. Beans that are defined in one container are not post-processed by a BeanPostProcessor in another container, even if both containers are part of the same hierarchy.

就是说@Value是通过BeanPostProcessor来处理的，而webapplicationContex和applicationContext是单独处理的，不是继承的，所以webapplicationContex不能使用父容器的属性值。

要作的就是单独给webapplicationContex设置property-placeholder

<!--spring-mvc.xml -->
<!-- 自动扫描且只扫描@Controller -->
	<context:component-scan base-package="com.xxxx.web" use-default-filters="false">
		<context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
		<context:include-filter type="annotation" expression="org.springframework.web.bind.annotation.ControllerAdvice"/>
	</context:component-scan>

<!-- 单独为webapplicationContext注入placeholder  -->
<context:property-placeholder ignore-unresolvable="true"
			location="classpath*:/application.properties" />	

这样就可以使用@Value为Controller注入属性了，还有个小前提，就是这个属性值不能是static的，static的@Value就没有效果了。