String paths are used in the different places of the Drill code:
FileSelection, Metadata, ParquetGroupScan, ReadEntryWithPath, FileWork, FormatSelection, FormatPlugin, PartitionLocation and so on.
Code with paths as strings is hard to test and maintain. And there are a lot of String to Path conversions and vice versa.
The aim of this jira to replace String paths with Hadoop Path. The job of the Path class is do properly implement file path operations, just as the job of the older File and newer Path classes in Java is to handle OS paths.
For the serialized structures a custom JsonSerializer<Path> and JsonDeserializer<Path> can be implemented.