Determines a {@link Map} with the file group identifier as key and the {@link FileGroup} instances as values. This groupingis based on an investigation in the absolute file names. If they match the given grouping pattern the first group of the pattern is replaced by an general token. If the resulting string from multiple files match now, they are grouped together.
For example the files
- admin_de_DE.properties
- admin_en_US.properties
and the grouping pattern ".*?_(\\w{2,3}_\\w{2,3}|\\w{2,3})\\.\\w*" will result in a group called "admin_{group}.properties" which holds references to these two files.
@see FileGrouper#setGroupingPatternString(String)
@see FileGroup