Why we declare </context:component-scan>separately in applicationContext.xml and dispatcher-servlet.xml

Question

Why sometimes we separately declare context:component-scan

in applicationContext.xml we declare like below:

<ctx:component-scan base-package="com.*"> <ctx:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller"/> </ctx:component-scan>

in dispatcher-servlet.xml we declare like below:

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

Why don't we just declare in applicationContext.xml as below :

<context:component-scan base-package="com.*"/>

Then all component annotated @Controller,@Service,@Repository will be detected

Answer 1

This separation is meant to allow multiple dispatcher servlets to be defined and the core business components to be reused.

Usually, you'll have stuff like repositories and services defined in the application-context.xml and bound to the entire servlet-context (by using a ContextLoaderListener) and have one or more dispatcher servlets defined, each with their own (child) context (consisting of controllers and mvc utility components) which will reuse the same beans from the parent context.

I would say this separation makes sense even if you have a single dispatcher, as it forces you to isolate the "core domain" from the application layer.