Can I inject the WebApplicationContext of my Spring MVC servlet into a DelegatingFilterProxy? - spring

Question

I am creating an OAuth authorization server that uses Spring Security as my security layer around parts of my servlet. An essential part of this is using the DelegatingFilterProxy to map to the springSecurityFilterChain bean, which requires a WebApplicationContext instance.
The standard solution is to include a ContextLoaderListener with associated contextConfigLocation configuration. But that entails creating a separate configuration for the root WebApplicationContext, needlessly complicating matters in my opinion.
According to the Spring MVC documentation, every DispatcherServlet has it's own WebApplicationContext instance. What's more, from perusing the code of DelegatingFilterProxy, it should be possible to inject a WebApplicationContext instance at construction time.
So my question is: Can I set the DispatcherServlet WebApplicationContext as the instance for DelegatingFilterProxy?
Here is the relevant configuration I have currently:
web.xml:
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">
<!-- Enable Spring Security -->
<filter>
<filter-name>springSecurityFilterChain</filter-name>
<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>
<filter-mapping>
<filter-name>springSecurityFilterChain</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>oauth</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/servlet.xml</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>oauth</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
</web-app>
servlet.xml:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:oauth="http://www.springframework.org/schema/security/oauth2"
xmlns:security="http://www.springframework.org/schema/security"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd
http://www.springframework.org/schema/security/oauth2
http://www.springframework.org/schema/security/spring-security-oauth2-1.0.xsd
http://www.springframework.org/schema/security
http://www.springframework.org/schema/security/spring-security.xsd">
<mvc:annotation-driven/>
<!-- ... Spring MVC config ... -->
<!-- Spring Security OAuth Config -->
<security:global-method-security pre-post-annotations="enabled" />
<oauth:authorization-server client-details-service-ref="clientDetails"
token-services-ref="tokenServices"
token-endpoint-url="/api/token">
<oauth:refresh-token/>
<oauth:client-credentials/>
</oauth:authorization-server>
<!-- ... loads more OAuth config ... -->
</beans>

Answer 1

DispatcherServlet (as any subclass of FrameworkServlet) will publish its WebApplicationContext in the ServletContext using the attribure name: org.springframework.web.servlet.FrameworkServlet.CONTEXT.<servlet-name>.
At the same time DelegatingFilterProxy can be told not to use the root WebApplicationContext but another one stored in the ServletContext by setting its contextAttribute parameter.
In your case the required config would be:
<filter>
<filter-name>springSecurityFilterChain</filter-name>
<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
<init-param>
<param-name>contextAttribute</param-name>
<param-value>org.springframework.web.servlet.FrameworkServlet.CONTEXT.oauth </param-value>
</init-param>
</filter>
See more about how DelegatingFilterProxy looks up the WebApplicationContext in the javadoc of findWebApplicationContext().