Property replacement in XML configuration files
Certain elements inside XML configuration files can use ${property-name} syntax. When this syntax is used, the referenced Java system property value will replace the property reference during configuration parsing.
Note:
If the system property does not exist, this will make the configuration parsing fail.
A classical use case for this feature is for providing a disk file location inside the directory attribute of the persistence tag:
<persistence directory="${user.home}/cache-data"/> <!-- 1 -->
1. Here user.home will be replaced by the value of the system property, for example /home/user.
The following attributes in the core configuration support system property replacement:

Local persistence directory (supports substitution within a string).

Thread pool minimum and maximum size attributes.

Write-behind queue size, concurrency, batch size and maximum batch delay.

Cache TTI and TTL.

Core resource sizes (heap, offheap and disk).

Disk store writer concurrency and segment count.