Cannot read Excel file in CodeIgniter - php

Question

I am facing a problem in a project which is uploading excel file through using the CodeIgniter3 and PHPExcel library.
The problem occurs when I upload an excel file, the file is uploaded successfully into the folder but it cannot be read. Further, it gives an error message:
Error loading file "xls_file": Could not open file ./assets/xls_file/ for reading.
So the data couldn't be saved into the database.
I want the system read the file inside the folder of xls_file, why is the system reading the xls_file as folder? My friend told me there may be problem in the URI in CodeIgniter 3, but we don’t know the solution how to fix the problem. Here’s my controller :
$fileName = time().$_FILES['file']['name'];
$config['upload_path'] = './assets/xls_file/'; //save excel file in folder
$config['file_name'] = $fileName;
$config['allowed_types'] = 'xls|xlsx|csv';
$config['max_size'] = 10000;
$this->load->library('upload');
$this->upload->initialize($config);
if(! $this->upload->do_upload('file') )
$this->upload->display_errors();
$media = $this->upload->data('file');
$inputFileName = './assets/xls_file/'.$media['file_name'];
try {
$inputFileType = IOFactory::identify($inputFileName);
$objReader = IOFactory::createReader($inputFileType);
$objPHPExcel = $objReader->load($inputFileName);
} catch(Exception $e) {
die('Error loading file "'.pathinfo($inputFileName,PATHINFO_BASENAME).'": '.$e->getMessage());
}
$sheet = $objPHPExcel->getSheet(0);
$highestRow = $sheet->getHighestRow();
$highestColumn = $sheet->getHighestColumn();
for ($row = 2; $row <= $highestRow; $row++){ // Read a row of data into an array
$rowData = $sheet->rangeToArray('A' . $row . ':' . $highestColumn . $row,
NULL,
TRUE,
FALSE);
//save into the column
$data = array(
"id_jalan"=> $rowData[0][0],
"id_kriteria"=> $rowData[0][1],
"nilai"=> $rowData[0][2],
"tahun_anggaran"=> $rowData[0][3],
"penanda"=> $rowData[0][4],
);
//save into the tabel
$insert = $this->db->insert("value",$data);
//delete_files($media['file_path']);
}
redirect('page/landing');