File Exists and Is Directory, But Listfiles() Returns Null

File exists and IS directory, but listFiles() returns null

For those with this problem, add this to AndroidManifest.xml:

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

Problem solved :D

EDIT: If this does not work just make sure if path is correct

Why can File.listFiles return null when called on a directory?

Add this to AndroidManifest.xml:

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

This permission allow you to read files; if you don't use this permission then listFiles() and list() will both throw NullPointerException.

And here is an example of showing all files in /storage/emulated/0/Download:

   String dir = "/storage/emulated/0/Download/";
        File f = new File(dir);
        String[] files = f.list();
        for(int i=0; i<files.length; i++){
            Log.d("tag", files[i]);
        }

listFiles() returns null when it shouldn't. It used to work properly until recently and hasn't been modified

On Windows 7 (and later) the process will have to run with elevated privileges to write to C:/Windows and similar directories. But if that was the problem it would result in a different error message.

What I suspect:
When running a 32-bit JVM under 64-bit Windows new File("C:/Windows/System32") will point to C:\Windows\SysWOW64 and there is no info-Folder under C:\Windows\SysWOW64\oobe

As a test:

public static void main(String[] args) {
    File sysdir = new File("C:/Windows/System32/oobe/info");
    for(File file:sysdir.listFiles()) {
        System.out.println(file.getName());
    }
}

runs fine with 64-bit-JRE and throws NullPointerException under 32-bit-JRE on Windows 7 64-bit.

So perhaps you or another application recently installed a 32-bit-jre or changed your path to point to a 32-bit-jre and thus broke your application.

file.listFiles() returns null even though folder exists

In order to access the files, the permissions must be given in the manifest file.

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

Add this in your MainActivity.java (not in same class as it wont work for 1st time when app is installed cuz of not being async)

checkPermissionReadStorage(this);

Try this:

String path = Environment.getExternalStorageDirectory().getAbsolutePath()+"/Android";
Log.d("Files", "Path: " + path);
File directory = new File(path);
File[] files = directory.listFiles();
if (files != null)
{
   Log.d("Files", "Size: "+ files.length);
   for (int i = 0; i < files.length; i++)
   {
       Log.d("Files", "FileName:" + files[i].getName());
   }
}

Add this method to your class, i was getting the same crash as you said but after adding this i get the proper result -

D/Files: FileName:data

public static void checkPermissionReadStorage(Activity activity) {
        if (ContextCompat.checkSelfPermission(activity,
                Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {

            if (!ActivityCompat.shouldShowRequestPermissionRationale(activity,
                    Manifest.permission.READ_EXTERNAL_STORAGE)) {
                ActivityCompat.requestPermissions(activity,
                        new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                        1);
            }
        }
    }

Let me know if you have any issue with this.

can only read folder/directory from main() ? listfiles() returns null?

Below code works fine, as long as path is correct. I assume your path must be invalid. As File::listFiles will return a null, if directory does not exist.

private List<String> get_files_paths(String data_path) {
    File folder = new File(data_path);
    if(!folder.exists() || !folder.isDirectory()){
        throw new IllegalArgumentException("Invalid directory");
    }
    List<String> full_paths = new ArrayList<>();
    for (File fileEntry : folder.listFiles()) {
        if (fileEntry.isFile())
            full_paths.add(fileEntry.getAbsolutePath());
    }
    return full_paths;
}

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