(Not Recuisive) Get list file type in android java

The problem is DocumentFile it is even specified in documentation that it is very slow:

It offers a simplified view of a tree of documents, but it has substantial overhead. For optimal performance and a richer feature set, use the DocumentsContract methods and constants directly.

also read this blog post: Scoped Storage Stories: DocumentsContract

As this blog entry and android documentation (above) suggests you should work directly with DocumentsContract. Actually what you should do is to write your own listFiles but optimized - see answer here https://stackoverflow.com/a/66296597/471160

[edit]

Below is a code which minimizes use of ContentProvider to list recursively file tree (but it does not use recursion - but a stack collection).

In your code replace:

DocumentFile[] F1 = F0.listFiles();
for (DocumentFile F2 : F1) {
  recuisiveUri(F2);
}

with:

listUri = traverseDirectoryEntries(resultUri);

Code is as follows (its based on Issues traversing through directory hierarchy with Android Storage Access Framework / DocumentProvider using MTP). I have not tested it on huge folder hierarchies - only on emulator. I am not sure if it properly filters for ".epub" - I think you should be able to handle it.

ArrayList<Uri> traverseDirectoryEntries(Uri rootUri) {
    ArrayList<Uri> listUri = new ArrayList<>();

    ContentResolver contentResolver = this.getContentResolver();
    Uri childrenUri = DocumentsContract.buildChildDocumentsUriUsingTree(rootUri,
            DocumentsContract.getTreeDocumentId(rootUri));

    // Keep track of our directory hierarchy
    List<Uri> dirNodes = new LinkedList<>();
    dirNodes.add(childrenUri);

    while(!dirNodes.isEmpty()) {
        childrenUri = dirNodes.remove(0); // get the item from top
        Log.d(LOG_TAG, "node uri: " + childrenUri);
        Cursor c = contentResolver.query(childrenUri, new String[]{
                DocumentsContract.Document.COLUMN_DOCUMENT_ID,
                DocumentsContract.Document.COLUMN_DISPLAY_NAME,
                DocumentsContract.Document.COLUMN_MIME_TYPE},
                null, null, null);
        try {
            while (c.moveToNext()) {
                final String docId = c.getString(0);
                final String name = c.getString(1);
                final String mime = c.getString(2);
                Log.d(LOG_TAG, "docId: " + docId + ", name: " + name + ", mime: " + mime);
                if(isDirectory(mime)) {
                    final Uri newNode = DocumentsContract.buildChildDocumentsUriUsingTree(rootUri, docId);
                    dirNodes.add(newNode);
                }
                else {
                    if (name.contains(".epub")) { // maybe you should check mime here?
                        final Uri newNode = DocumentsContract.buildChildDocumentsUriUsingTree(rootUri, docId);
                        listUri.add(newNode);
                    }
                }
            }
        } finally {
            closeQuietly(c);
        }
    }
    return listUri;
}

// Util method to check if the mime type is a directory
private static boolean isDirectory(String mimeType) {
    return DocumentsContract.Document.MIME_TYPE_DIR.equals(mimeType);
}

// Util method to close a closeable
private static void closeQuietly(Closeable closeable) {
    if (closeable != null) {
        try {
            closeable.close();
        } catch (RuntimeException re) {
            throw re;
        } catch (Exception ignore) {
            // ignore exception
        }
    }
}

I think your problem is fairly simple provided you are comfortable with Kotlin.

Here's how you can get all .epub files in a directory:

val rootDir = File(uri.path) // uri pointing towards the chosen directory
val allEpubFiles = root.list { dir, name -> name.endsWith(".epub") }