title: <springProperty> in logback-spring.xml not working with externalized application.properties
body: <p>I have my spring boot application.properties loaded from file system with @PropertySource on my @Configuration class. </p>
  
  <p>If I want to use application properties in my logback-spring.xml with <code>&lt;springProperty&gt;</code> tag, it is not working.  </p>
  
  <p>But if I place the application.properties in the classpath under src/main/resources, the <code>&lt;springProperty&gt;</code> tag works.</p>
  
  <p>Any idea why it is not working with externalized application.properties loaded with @PropertySource annotation ?  </p>