Current implementation of SpoolDirectorySource does not allow users to specify a regex pattern to select which files should be monitored. Instead, the current implementation allows users to specify which should not monitored, via the ignorePattern parameter.
I implemented the feature, allowing users to specify the include pattern as a1.sources.src-1.includePattern=^foo.*$ (includes all the files that starts in "foo").
By default, the includePattern regex is set to ^.*$ (all files). Include and exclude patterns can be used at same time and the results are combined.