Java Utililty Methods File List Load

File[] listOfFiles = sourceDirectory.listFiles(new FilenameFilter() {
    @Override
    public boolean accept(File directoryName, String filename) {
        return filename.endsWith(extension)
                && new File(directoryName + File.separator + filename).canRead();
});
return Arrays.asList(listOfFiles);
...

List<File> files = new ArrayList<File>();
for (int i = 0; i < fileArray.length; i++) {
    File file = fileArray[i];
    files.addAll(getList(file));
return files;

if (dir == null) {
    throw new IllegalArgumentException("Directory must not be null");
final File[] files = dir.listFiles();
if (files == null) {
    return;
for (final File file : files) {
...

final File[] list = root.listFiles();
if (list == null) {
    return;
for (final File f : list) {
    if (f.isDirectory() && !isIgnored(ignoreList, f)) {
        getFileList(fileList, f, ignoreList);
    } else {
...

File file = new File(location);
if (file.isDirectory()) {
    return file.list();
return null;

Map<T, List<String>> dirMap = map.get(dir);
if (dirMap == null)
    map.put(dir, dirMap = new HashMap<T, List<String>>());
List<String> files = dirMap.get(key);
if (files == null)
    dirMap.put(key, files = new ArrayList<String>());
return files;

List<String> fileList = new ArrayList<String>();
File _dir = new File(dir);
File[] files = _dir.listFiles();
if (files != null) {
    for (int i = 0; i < files.length; i++) {
        if (files[i].isFile()) {
            String fileName = files[i].getAbsolutePath();
            fileList.add(fileName);
...

try {
    File parent = new File(dir);
    if (!parent.isAbsolute() || !parent.isDirectory()) {
        return null;
    return parent.list();
} catch (Exception e) {
    return null;
...

File folder = new File(dir);
fileList = new ArrayList<File>();
traverse(folder, extension);
File[] fileArray = new File[fileList.size()];
fileList.toArray(fileArray);
return fileArray;

File f = new File(dir);
if (!f.exists())
    return Collections.EMPTY_LIST;
if (!f.isDirectory())
    return Arrays.asList(f.getName());
List<String> names = new ArrayList<>(Arrays.asList(f.list(new FilenameFilter() {
    public boolean accept(File dir, String name) {
        return name.toLowerCase().endsWith(suffix) && !name.startsWith(".");
...