I was using classpath*: resource for Spring application context loading. All context definition files are in the
/WEB-INF/classes/appCtx directory and its subdirectories.

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath*:appCtx/**/*.xml</param-value>
</context-param>

However, when I enabled Spring Security in my web application, I got the exception:

org.springframework.beans.factory.parsing.BeanDefinitionParsingException: Configuration problem: Duplicate <http> element detected|Offending resource: ServletContext resource [/WEB-INF/classes/appCtx/applicationContext-security.xml]

The solution is pretty simple – move the security context configuration (e.g. applicationContext-security.xml) to a different directory outside appCtx and load it directly:

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>
        classpath*:appCtx/**/*.xml
        /WEB-INF/applicationContext-security.xml
    </param-value>
</context-param>