Annotation-based filters for component scanning find meta-annotations as well

[kingrockw]

<context:component-scan base-package="cn.rock">
    <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Component"></context:exclude-filter>
</context:component-scan>

Why can't the DispatcherServlet load the @Controller class in Spring MVC config according to the above configuration?

[sbrannen]

Although this kind of question is better suited for Stack Overflow, I'll go ahead and answer your question here.

1. @Controller is meta-annotated with @Component.
2. You have configured an exclude filter for classes annotated with @Component.
3. When specifying type="annotation" with <context:exclude-filter ... />, Spring creates an org.springframework.core.type.filter.AnnotationTypeFilter that by default considers annotations that are directly present or meta-present.

The net result is that you have instructed Spring to exclude from component scanning any classes that are directly annotated with @Component or meta-annotated with @Component (e.g., @Controller, @Service, @Repository, etc.). Thus, the DispatcherServlet does not see your @Controller class, because your @Controller class has been excluded from component scanning.

If you would like to exclude exactly classes annotated directly with @Component, you will need to implement a custom org.springframework.core.type.filter.TypeFilter. The easiest way would be to extend AnnotationTypeFilter and have the default constructor of your subclass delegate to the AnnotationTypeFilter(Class<? extends Annotation>, boolean) -- for example super(Component.class, false).

You can then specify type="custom" and expression="org.example.MyCustomComponentAnnotationTypeFilter" in <context:exclude-filter ... />.

[sbrannen]

@kingrockw, thanks to your question I noticed that the documentation was not explicit with regard to the default support for meta-annotations. I have therefore updated the documentation in b109f14.

Cheers!

[sbrannen]

As an alternative to my previous proposal to implement a custom TypeFilter, if you are activating the component scanning in an XML configuration file that is solely dedicated to loading web-related beans, you may wish to simply include only classes annotated with @Controller, which you should be able to achieve as follows.

<context:component-scan base-package="cn.rock" use-default-filters="false">
    <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller" />
</context:component-scan>

[kingrockw]

Thank you very much for your answer. @sbrannen