application-context.xml

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       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">

    <context:property-placeholder location="file:appConfigOverride.properties" order="-1"
                                  ignore-unresolvable="true" ignore-resource-not-found="true" />
    <context:property-placeholder location="classpath:appConfig.properties" />

    ....

</beans>