ResourceBundle file outside jar

Question

I have a spring boot application with /resources/application.properties, when deployed there is a application.properties next to the jar (and the one inside it).

Somewhere in the code I use ResourceBundle.getBundle("application").getString("x") but that always return the value defined in the properties inside the jar.

My objective is to get the value from the external file if it exists, if not then I need to get the value from inside the jar. Just like the default springs behavior but I'm not able to achieve this.

edit:

You can either use the solution in the correct answer below or you can rely on springs Environment by autowiring it and using getProperty()

Answer 1

ResourceBundle.getBundle(String baseName) relies on the classloader and not directly the file system to find the resource.
This is equivalent to invoke the overloaded one :

getBundle(baseName, Locale.getDefault(), this.getClass().getClassLoader()), 

So your result is expected.
What you look for is PropertyResourceBundle.
To create an instance of you need either a Reader or an InputStream.

You could load both external and internal files.

ResourceBundle internalProps = ResourceBundle.getBundle("application");
ResourceBundle externalProps = new  PropertyResourceBundle(Files.newInputStream(Paths.get("application.properties"));

You could so use the external ResourceBundle in first intention and the second one as fallback.