Wrapping the application.name value with '#', what does it mean? - spring

Question

What does adding the '#' to name value of application.properties to the beginning and to the end mean?
I couldn't find usage of something like this. I checked the Spring docs as well, but I couldn't find it. Is this usage a generic thing for programming or specific to application.properties of Spring?

Answer 1

Please go through the documentation
Rather than hardcoding some properties that are also specified in your
project’s build configuration, you can automatically expand them by
instead using the existing build configuration. This is possible in
both Maven and Gradle.
The format you mentioned is for Maven
You can automatically expand properties from the Maven project by
using resource filtering. If you use the spring-boot-starter-parent,
you can then refer to your Maven ‘project properties’ with #..#
placeholders
Update
With Spring Boot Actuator dependency added to pom.xml
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
and
info endpoint exposed (for http : management.endpoints.web.exposure.include=info )
a quick verification of this can be done.
Add the following property to pom.xml
<properties>
<app.info.test>Test Value</app.info.test>
</properties>
and following entries in the application.properties file
info.app.name= Test App
info.app.java.source=1.8
info.app.test=#app.info.test#
Hitting http://localhost:8080/actuator/info will give the following response
{"app":{"name":"Test App","java":{"source":"1.8"},"test":"Test Value"}}

Answer 2

Straight Forward answer is the value which you store with #name# in application.properties are initialized when your project build start (based on same parameter name you pass with command).
It's used when you want to pass value of that variable at time of build
or value which are different based on environment.If you don't do that then it value becomes fixed.
when you're want to pass some parameter which are constant or repetitively use in your application like mail configuration or AWS configuration, version or etc. that things define in application.properties file.