Spring 无法处理“multipart/form-data”POST 请求（错误 400“Bad request”）

Question

当我向此服务器代码发布请求时 - 一切正常：

@RequestMapping(method = RequestMethod.POST, consumes = { "application/json" })
public ResponseEntity<String> addQuestion(@RequestBody String dtoObject) { ... }

但如果我将请求更改为“multipart/form-data” - Spring 返回错误 400“Bad request”：

@RequestMapping(method = RequestMethod.POST, consumes = { "multipart/form-data" })
public ResponseEntity<String> addQuestion(@RequestBody String dtoObject) { ... }

为什么？ 可能我应该创建一些额外的 bean 吗？

PS：我需要“multipart/form-data”来将文件与 json 对象一起发送。

Answer 1

我认为您无法将文件反序列化为请求正文中的该 dtoObject。你需要使用@RequestPart 来做到这一点。

@RequestMapping(method = RequestMethod.POST, consumes = { "multipart/form-data" })
public ResponseEntity<String> addQuestion2(@RequestPart("question") QuestionPostDto dtoObject, @RequestPart("file") MultiPartFile file)  { ... }

您的请求需要是formdata：带有您要上传的文件和json格式文件question.json

这是我的来自 post man 的有效负载示例

Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW

------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="file"; filename="QLbLFIR.gif"
Content-Type: image/gif


------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="question"; filename="question.json"
Content-Type: application/json


------WebKitFormBoundary7MA4YWxkTrZu0gW--

或者如果你不想传递一个json格式的文件你可以用一个普通的字符串传递它

@RequestMapping(method = RequestMethod.POST, consumes = { "multipart/form-data" })
    public ResponseEntity<String> addQuestion2(String question, @RequestPart("file") MultiPartFile file)  {
    QuestionPostDto dtoObject = new ObjectMapper().readValue(request, QuestionPostDto.class); 
    // do sth
}

Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW

------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="file"; filename="QLbLFIR.gif"
Content-Type: image/gif


------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="request"

{
    "key": "value"
}
------WebKitFormBoundary7MA4YWxkTrZu0gW--

更多详情请参阅此主题： Spring MVC Multipart Request with JSON

Answer 2

我解决了这个问题。

1) 我创建了 HttpMessageConverter，它将 json 转换为我的自定义类型 QuestionPostDto：

public class QuestionPostDtoHttpMessageConverter implements HttpMessageConverter<QuestionPostDto> {

    @Override
    public boolean canRead(Class<?> clazz, MediaType mediaType) {
        return QuestionPostDto.class == clazz;
    }

    @Override
    public boolean canWrite(Class<?> clazz, MediaType mediaType) {
        return QuestionPostDto.class == clazz;
    }

    @Override
    public List<MediaType> getSupportedMediaTypes() {
        List<MediaType> list = new ArrayList<MediaType>();
        list.add(MediaType.MULTIPART_FORM_DATA);
        return list;
    }

    @Override
    public QuestionPostDto read(Class<? extends QuestionPostDto> clazz, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException {
        InputStream istream = inputMessage.getBody();
        String requestString = IOUtils.toString(istream, "UTF-8");

        ObjectMapper mapper = new ObjectMapper();
        return mapper.readValue(requestString, QuestionPostDto.class);
    }

    @Override
    public void write(QuestionPostDto t, MediaType contentType, HttpOutputMessage outputMessage)
            throws IOException, HttpMessageNotWritableException {
    }
}

2）我为这种类型的HttpMessageConverter创建bean（我们在项目中使用Spring Boot）：

@Configuration
public class HttpConfiguration {
...
    @Bean
    public QuestionPostDtoHttpMessageConverter commonsMultipartResolver() {
        return new QuestionPostDtoHttpMessageConverter();
    }
}

3) 现在我在 RestController 中的代码可以正常工作了：

@RestController
@RequestMapping("/api/question")
@ConfigurationProperties(prefix = "question")
@RequiredArgsConstructor
@Slf4j
public class QuestionController {
...
@PostMapping
ResponseEntity<String> addQuestion(@RequestPart("dtoObject") QuestionPostDto dtoObject, @RequestPart("file") MultipartFile file) { ... }

感谢大家，尤其是Chi Dov