How do you specifiy a Properties File for Placeholder Properties in Spring Configuration Files?

If you have a Spring Configuration File with Placeholder Properties the properties get replaced with a light-grey value of the property.

Where does it find these properties? As far as I can tell it almost looks like it takes them from any properties file in the project.

How do I tell it specifically which Properties File to use?

Also, as seen in the image, once you actually click the light-grey property it reverts back to the placeholder.