PreparedFoldersMapText - Prepares raw data to map 
[key, value]: [folder name, instance of Folder with list of files of this folder].

public PreparedFoldersMapText(PreparedFolders<Map<String, List<String>>> prepFolders)

PreparedFolders<Map<String, List<String>>> prepFolders - decoration (default PreparedFoldersMapRaw).

List<String> rawFiles = new ArrayList<>();
        rawFiles.add("/file1.txt");
        rawFiles.add("/file2.txt");
        rawFiles.add("/root1.txt");
        rawFiles.add("/root2.txt");
        rawFiles.add("/root3.txt");
        rawFiles.add("/folder1/file1.txt");
        rawFiles.add("/folder1/file2.txt");
        rawFiles.add("/folder2/file1.txt");

PreparedFolders<Map<String, Folder<String>>> prepFolders = new PreparedFoldersMapText(
        new PreparedFoldersMapRaw(rawFiles));

Map<String, Folder<String>> mapFolder = prepFolders.preparation();
mapFolder.forEach((fullFolderName, folder) -> {
        System.out.println(fullFolderName); 
        prepFiles.forEach(folder ->
            folder.files().forEach(file -> System.out.println("\t" + file))
        );
    }
);