swagger 文件上传

以下写在API接口类：
@ApiOperation(value = "导入用户", notes = "导入用户", response = String.class, tags = {})
    @ApiResponses(value = { @ApiResponse(code = 200, message = "successful operation", response = String.class),
            @ApiResponse(code = 400, message = "Invalid mobile supplied", response = String.class),
            @ApiResponse(code = 404, message = "server not available", response = String.class) })
    @RequestMapping(value = "/importCustomer", produces = { "application/json"}, method = RequestMethod.POST)
    ResponseEntity<String> importCustomer(@RequestParam("importFile") MultipartFile importFile);
以下是实现：
public ResponseEntity<String> importCustomer(@RequestParam("importFile") MultipartFile importFile) {
    return new ResponseEntity<String>(