深入研究之后，我可以在Spring WebFlux项目中找到此测试：
https://github.com/spring-projects/spring-framework/blob/master/spring-
webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/MultipartIntegrationTests.java
因此，部分我缺少的是
@RequestPart，而不是
@RequestBody在控制器中定义。
最终代码如下所示：
@RestController@RequestMapping("/images")public class ImageController { @Autowired private IImageService imageService; @PostMapping(value = "", consumes = MediaType.MULTIPART_FORM_DATA_VALUE, produces = MediaType.APPLICATION_JSON_VALUE) Mono<ImageEntity> saveImage(@RequestPart("file") Mono<FilePart> part) throws Exception{ return part.flatMap(file -> imageService.saveImage(file)); }}
