springboot Fast Restart will not respect the changing of maven resource delimiter for YAML configuration file

Issue This is the follow up of the issues https://github.com/spring-projects/spring-boot/issues/8438 https://github.com/spring-projects/spring-boot/issues/8689 regarding to change the maven resource delimiter to remedy the parsing error of YAML file.

I found that if I changed the maven resource delimiter to some valid characters, the lookup will failed after Fast Restart.

e.g. In my pom.xml, I add the following to change the default resource delimiter. <resource.delimiter>QQQ</resource.delimiter>

In my application.yml,

app:
   myProperty: QQQmyPropertyValueQQQ

The QQQmyPropertyValueQQQ is correctly substituted to the property value in pom.xml during startup. However, if I touch the application.yml to trigger the fast restart, the QQQmyPropertyValueQQQ lookup will fail. It will retain the value QQQmyPropertyValueQQQ and not substituted.

Comment From: wilkinsona

I don't think this has anything to do with changing the delimiter. If you don't involve your build system in the change then nothing is going to perform the filtering. This is already being discussed in #5136

Comment From: fy-kenny

I solved issue like this https://github.com/yaml/yaml/issues/51