import static java.nio.file.FileVisitResult.*;                         // Import constants
import java.nio.file.*;
import java.nio.file.attribute.*;
import java.io.IOException;

public class ListFiles extends SimpleFileVisitor<Path> {
  // Output the directory path and set indent for entries
  @Override
  public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attr) {
    System.out.format("\n%sDirectory: %s contains:", indent, dir);
    indent.append("  ");
    return CONTINUE;
  }

    // Note error after walking directory and reset indent
    @Override
    public FileVisitResult postVisitDirectory(Path dir, IOException e) {
      if(e != null) {
        System.err.format("\n%sError walking directory: %s\n%s", indent, dir, e);
      }
     int len = indent.length();
     indent.delete(len-2, len);
     return CONTINUE;
    }

    // Record file or symbolic link details
    @Override
    public FileVisitResult visitFile(Path file, BasicFileAttributes attr) {
      if(attr.isRegularFile()) {
          System.out.format("\n%sFile: %s", indent, file);
      } else if (attr.isSymbolicLink()) {
        System.out.format("\n%sSymbolic link: %s", indent, file);
      }
      return CONTINUE;
    }

    // Record file visit failure
    @Override
    public FileVisitResult visitFileFailed(Path file, IOException e) {
      System.out.format("\n%sFile attributes could not be read for: %s\n%s",
                                                                        indent, file,e);
      return CONTINUE;
    }

   private StringBuilder indent = new StringBuilder("  ");             // Indent for entries
}