Working with Ant Properties File
Ant properties files let you move properties out of your build.xml file.
.properties file for all the properties that are defined outside the build file. For example, properties that you define in build settings. IntelliJ IDEA keeps those properties in one place and you don't need to edit the generated build file.
Include a property in your build.xml file with the name of the properties file specified by the file attribute. For example,