Explain File upload handling in Laravel with code examples.

public function store(Request $request) {
    $request->validate([
        "avatar" => "required|image|mimes:jpeg,png,jpg|max:2048"
    ]);
    
    $path = $request->file("avatar")->store("avatars", "public");
    
    auth()->user()->update(["avatar" => $path]);
}

public function uploadDocument(Request $request) {
    if ($request->hasFile("document")) {
        $file = $request->file("document");
        $filename = time() . "." . $file->getClientOriginalExtension();
        
        $file->storeAs("documents", $filename, "public");
        
        Document::create([
            "name" => $file->getClientOriginalName(),
            "path" => "documents/" . $filename,
            "size" => $file->getSize(),
        ]);
    }
}

public function uploadMultiple(Request $request) {
    $request->validate([
        "files.*" => "required|file|max:10240"
    ]);
    
    foreach ($request->file("files") as $file) {
        $file->store("uploads", "public");
    }
}