spring.datasource.url=jdbc:mysql://${DB_HOST}:${DB_PORT}/${DB_NAME}
spring.datasource.username=${MYSQL_USER}
spring.datasource.password=${MYSQL_PASSWORD}

/gradlew clean build bootJar -DDB_HOST=mock -DDB_PORT=mock -DDB_NAME=mock
-Dmysql_user=mock
-Dmysql_password=mock

java -jar build/libs/MyApplication.jar -Ddb_host=localhost
-Ddb_port=3306
-Ddb_name=my_db
-Dmysql_user=root
-Dmysql_password=root

...
Failed to parse the host:port pair '${DB_HOST}:${DB_PORT}'
...
java.lang.NumberFormatException: For input string: "${DB_PORT}"
...