Recursive search in all directories and Ubdirectories of a given folder

Question

I am developing a script to scan a particular folder for certain files and delete them or move them to another folder, according to some rules I already got answered in this question and in this other question.

My idea was to abstract this search by saving all found files (either to move or to delete) into a list and later make a decision as to the operation, only that I don’t have much idea of how to do a search in a certain folder and its entire internal directory tree that are being found.

private static List<File> listarArquivos(File source, boolean condicao) {
    List<File> fileList = new ArrayList<>();

    File[] list = source.listFiles();

    for (File fl : list) {
        if (condicao) {
            fileList.add(fl);
            System.out.println(fl);
        }
    }

    return fileList;

}

This method only lists the subfolders and files from the main directory, but does not list more internal files and folders, how to do this recursively?

_{Note: in case of solutions using java-8, I ask for a brief explanation, as I am not very familiar with the new classes of this version.}

Answer 1

Just do a check if fl is a directory using File.isDirectory() and call the method again by passing fl as a parameter.

private static List<File> listarArquivos(File source) 
{
    List<File> fileList = new ArrayList<>();

    File[] list = source.listFiles();

    for (File fl : list) {
        if (!fl.isDirectory()) {
            fileList.add(fl);
            System.out.println(fl);
        }else{
            System.out.println(String.format("** Pasta: %s **", fl));
            listarArquivos(fl);
        }
    }

    return fileList;
}

Answer 2

Using Java 8 you can use the method walk class Files:

List<Path> lista = new ArrayList<>();

Files.walk(Paths.get("C:/D/Desktop/Workshop"))
        .filter(arquivo -> this.filtrar(arquivo))
        .forEach(lista::add);

Or if you wanted to return a list of File:

List<File> lista = new ArrayList<>();

Files.walk(Paths.get("C:/D/Desktop/Workshop"))
        .filter(arquivo -> this.filtrar(arquivo))
        .forEach(arquivo -> {
          lista.add(arquivo.toFile());
        });

whereas the method filtrar be it so (based in this answer):

private boolean filtrar(Path caminho) {
  return caminho.toString().matches("Copia - Copia\\.[^.]+$");
}

Files walk.

Returns a Stream that ociosamente(Lazy) populace with Path traversing the file tree starting with the initial file

Adapting to your method:

private static List<File> listarArquivos(File source, boolean condicao) throws IOException {
  List<File> fileList = new ArrayList<>();

  Files.walk(source.toPath()).forEach(arquivo -> {
    if (condicao) {
      fileList.add(arquivo.toFile());
    }
  });

  return fileList;
}