import java.nio.file.*;
import java.io.IOException;

public class ListDirectoryContents {
  public static void main(String[] args) {
    Path currentPath = Paths.get(System.getProperty("user.dir"));
    currentPath = currentPath.getParent();

    // Get the entire directory contents
    filterDirectoryContents(currentPath, null);

    // Now try a filter for .txt files
    System.out.println("\nFilter for .txt:");
    filterDirectoryContents(currentPath, "*.txt");

    // Get files with a 3 character extension begiining with 'j'
    System.out.println("\nFilter for .j??:");
    filterDirectoryContents(currentPath, "*.j??");
  }

  // Filter the contents of a directory
  private static void filterDirectoryContents(Path path, String filter) {
    try (DirectoryStream<Path> paths = filter != null ? Files.newDirectoryStream(path, filter):Files.newDirectoryStream(path)){
      System.out.println("\n" + path + " directory contains:");
      for(Path p : paths) {
        System.out.println("  " + p.getFileName() + (Files.isDirectory(p) ? " is a directory." : ""));
      }
    } catch(NotDirectoryException e) {
    System.err.println("Path is not a directory." + e);
    } catch(IOException e) {
      System.err.println("I/O error." + e);
    }
  }
}