Spring MVC POST request with dto that contains multipart files and other dtos

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Please help with answer for this question

I have a DTO that contains other DTOs and a list of multipart files. I am trying to process that DTO but I can't seem to be able to read the requst.

class TeacherDTO {
   private SpecializationDto specializationDto;
   private List<MultipartFile> files;
}

@PostMapping(consumes = {MediaType.MULTIPART_FORM_DATA_VALUE},
            produces = {MediaType.APPLICATION_JSON_VALUE})
public ResponseEntity<Object> saveNewTeacher(@ModelAttribute @Valid TeacherDTO teacherDto){

//process request

}

When creating an example request from Swagger UI, I get the following exception:

type 'java.lang.String' to required type 'SpecializationDto' for property 'specializationDto': no matching editors or conversion strategy found

If I put @RequestBody instead of @ModelAttribute then I get

Content type 'multipart/form-data;boundary=----WebKitFormBoundaryVEgYwEbpl1bAOjAs;charset=UTF-8' not supported]

Swagger dependencies:

<dependency>
   <groupId>org.springdoc</groupId>
   <artifactId>springdoc-openapi-ui</artifactId>
   <version>1.5.2</version>
</dependency>
<dependency>
   <groupId>org.springdoc</groupId>
   <artifactId>springdoc-openapi-data-rest</artifactId>
   <version>1.5.2</version>
</dependency>

OpenAPI3.0 config:

@Configuration
public class OpenApi30Config {

  private final String moduleName;
  private final String apiVersion;

  public OpenApi30Config(
      @Value("${spring.application.name}") String moduleName,
      @Value("${api.version}") String apiVersion) {
    this.moduleName = moduleName;
    this.apiVersion = apiVersion;
  }

  @Bean
  public OpenAPI customOpenAPI() {
    final var securitySchemeName = "bearerAuth";
    final var apiTitle = String.format("%s API", StringUtils.capitalize(moduleName));
    return new OpenAPI()
        .addSecurityItem(new SecurityRequirement().addList(securitySchemeName))
        .components(
            new Components()
                .addSecuritySchemes(securitySchemeName,
                    new SecurityScheme()
                        .name(securitySchemeName)
                        .type(SecurityScheme.Type.HTTP)
                        .scheme("bearer")
                        .bearerFormat("JWT")
                )
        )
        .info(new Info().title(apiTitle).version(apiVersion));
  }
}

Answer 1

Have you tried to use @RequestMapping instead of @PostMapping? Something like this:

@RequestMapping(value = "/ex/foos", method = RequestMethod.POST)
public ResponseEntity<Object> saveNewTeacher(@Valid @RequestBody TeacherDTO teacherDTO) throws Exception {
    //process instance
}

class TeacherDTO {
   @Valid
   private SpecializationDto specializationDto;
   private List<MultipartFile> files;
}

//supposing your nested DTO is something like that
class SpecializationDto {
    @NotNull
    @NotEmpty
    String something;
}

Answer 2

This seems to be an issue with how the springdoc-openapi-ui build the form-data request. I was able to reproduce this and noticed that it sends a multipart-request like (intercepted through browser's dev-tools):

-----------------------------207598777410513073071314493349
Content-Disposition: form-data; name="specializationDto"


-----------------------------207598777410513073071314493349
Content-Disposition: form-data; name="files"; filename="somefile.txt"
Content-Type: application/octet-stream

<content>

-----------------------------207598777410513073071314493349
Content-Disposition: form-data; name="files"; filename="somefile.txt"
Content-Type: application/octet-stream

<content>

With that payload Spring is not able to deserialize the specializationDto , resulting in the "no matching editors or conversion strategy found" exception that you've observed. However, if you send the request through postman or curl with

curl --location --request POST 'http://localhost:8080/upload' \
--form 'files=@"/path/to/somefile"' \
--form 'files=@"/path/to/somefile"' \
--form 'specializationDto.something="someValue"'

Spring is able to parse it correctly. Here's my rest-mapping that will log the following as expected:

    @RequestMapping(value = "/upload", method = RequestMethod.POST, 
                    consumes = {MediaType.MULTIPART_FORM_DATA_VALUE})
    public void upload(@ModelAttribute TeacherDto requestDto) {
        System.out.println(requestDto);
    }


// logs:
TeacherDto(specializationDto=SpecializationDto(something=someValue), files=[org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile@78186ea6, org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile@461c9cbc])

I suggest you open a bug on their github page .