SpringBoot实现接口提供下载文件

	public ResponseEntity<FileSystemResource> export(File file) {
	    if (file == null) {
	        return null;
	    }
	    HttpHeaders headers = new HttpHeaders();
	    headers.add("Cache-Control", "no-cache, no-store, must-revalidate");
	    headers.add("Content-Disposition", "attachment; filename=" + System.currentTimeMillis() + ".xls");
	    headers.add("Pragma", "no-cache");
	    headers.add("Expires", "0");
	    headers.add("Last-Modified", new Date().toString());
	    headers.add("ETag", String.valueOf(System.currentTimeMillis()));

	    return ResponseEntity
	            .ok()
	            .headers(headers)
	            .contentLength(file.length())
	            .contentType(MediaType.parseMediaType("application/octet-stream"))
	            .body(new