gistfile1.txt

Validation file:
X\YBundle\Entity\ContactsUpload:
    properties:
        name:
            - NotBlank: ~
        file:
            - File:
                maxSize: 1024k
                mimeTypes: 'application/vnd.oasis.opendocument.spreadsheet'
                mimeTypesMessage: Please upload valid spreadsheet file!

Annotations: 
    /**
     * @Assert\File(
     *     maxSize="1M"
     *     mimeTypes={"application/vnd.ms-excel"},
     *     mimeTypesMessage="Please upload valid spreadsheet file!"
     * )
     */
    public $file;