https://java.qbytesworld.com/post/Externalizing-Bean-Configurations.aspx
http://almaer.com/blog/spring-propertyplaceholderconfigurer-a-nice-clean-way-to-share
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http://robertmarkbramprogrammer.blogspot.com/2008/02/nested-property-placeholders-in-spring.html
http://www.summa-tech.com/blog/2009/04/20/6-tips-for-managing-property-files-with-spring/