php怎么样把xls转换成csv ？如何实现Excel的xls和xlsx文件转换成csv文件

$filename = "myexcel.xlsx";

$objReader = PHPExcel_IOFactory::createReader('Excel2007');

$objPHPExcel = $objReader->load($filename);

$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'CSV');

$objWriter->save(str_replace('.xlsx', '.csv',$filename));