[Spring] replace MultipartFile by Resource

[martin-mfg]

fix #18345

To reproduce the problem, it's sufficient to use the spring generator with delegatePattern=true on this input:

openapi: 3.0.3
info:
  title: Swagger Petstore - OpenAPI 3.0
  description: ''
  version: 1.0.0
paths:
  /dummy:
    post:
      description: ''
      operationId: uploadFile
      requestBody:
        content:
          application/octet-stream:
            schema:
              type: string
              format: binary
      responses:
        '200':
          description: successful operation

The output doesn't compile.
(edit: added mention of delegatePattern and fixed the input spec above.)

As far as I can tell, the spring generator was meant to switch to using Resource instead of MultipartFile in all cases. But some places in the templates were not adjusted. I did this now in this PR. And it worked well in all scenarios I could test.
(The server generated here runs, but requests to the /multipart-mixed endpoint didn't work out of the box for me, due to "Unsupported Media Type". Both before and after my changes. So that's probably a different issue.)

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[MelleD]

Should this not be a MultipartFileResource?
https://docs.spring.io/spring-framework/docs/5.1.8.RELEASE_to_5.1.9.RELEASE/Spring%20Framework%205.1.9.RELEASE/org/springframework/web/multipart/MultipartFileResource.html

See source:
https://github.com/spring-projects/spring-framework/blob/main/spring-web/src/main/java/org/springframework/web/multipart/MultipartFileResource.java

[martin-mfg]

Should this not be a MultipartFileResource?

Good question. I used org.springframework.core.io.Resource because that's what other parts of the spring generator are using already for files. see e.g. here

I anyway wanted to try MultipartFileResource after reading your comment. But it turns out this is not possible/not intended, because MultipartFileResource is actually not a public class.

(Since Resource is more generic than MultipartFileResource, another consideration would be to keep our generated interfaces as generic as possible.)

So I guess I'll keep using Resource. Do you agree?

[MelleD]

Hey @martin-mfg Iam unsure if really Resource is right for a Multipart. I don't know why the other API are using it.

We are using MultipartFile and there is method

	default Resource getResource() {
		return new MultipartFileResource(this);
	}

See: https://docs.spring.io/spring-framework/reference/web/webmvc/mvc-controller/ann-methods/multipart-forms.html

Did you try if a resource is really working as MultiPart? Or can you then cast the Resource to a MultiPartResource?

[martin-mfg]

SpringCodegen briefly used MultipartFile in the past, but then switched (back) to Resource. see #9555 for the change itself, and the links there for people encountering problems with MultipartFile.

Did you try if a resource is really working as MultiPart?

Yes, the generated server works and can receive multipart requests.

Or can you then cast the Resource to a MultiPartResource?

The actual type of the Resource parameter was ByteArrayResource in my test. But I guess this depends on the concrete input spec. And Resource can not be cast to MultiPart(Resource).

Can you explain a bit more what problems you see with using Resource? It sounds like you already have a generated spring server which uses MultiPartFile. But as described in #18345, this shouldn't even compile in the first place.

Anyway, I do agree that MultiPartFile might actually be more useful than Resource, if the problems from #9555 can be avoided. But in that case I would like to keep the focus of this PR on fixing the compilation problem described in #18345. Making SpringCodegen generally use MultiPartFile instead of Resource should then be a separate PR. Does that sound good to you?

[MelleD]

Currently we have Spring Api with MultiPart. I can check my settings and which version. We also use the generated Spring Client. So this will then break our current Api and client. That's my point. And we need for a bigger upload a multipart.

I will look into the issue on monday or tuesday and come back with my generated code + settings

[MelleD]

That's the generated code with open api generator 7.5.0

Spring Java

    @RequestMapping(
        method = RequestMethod.POST,
        value = "/packages",
        produces = { "application/json" },
        consumes = { "multipart/form-data" }
    )
    
    ResponseEntity<MyDto> uploadPackage(
         @RequestPart(value = "file", required = true) MultipartFile file
    );

Open API yaml

  /packages:
    post:
      tags:
        - Package
      operationId: uploadPackage
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              required:
                - file
              properties:
                file:
                  type: string
                  format: binary

Maven setting

                  <configuration>
                     <inputSpec>${project.basedir}my-api.yaml</inputSpec>
                     <generatorName>spring</generatorName>
                     <configOptions>
                        <library>spring-cloud</library>
                        <useSpringBoot3>true</useSpringBoot3>
                        <dateLibrary>java8</dateLibrary>
                        <useOptional>true</useOptional>
                        <singleContentTypes>false</singleContentTypes>
                        <hateoas>true</hateoas>
                        <useSwaggerUI>false</useSwaggerUI>
                        <useTags>true</useTags>
                        <documentationProvider>none</documentationProvider>
                     </configOptions>
                  </configuration>

And here is the spring guide:

[martin-mfg]

Thanks for the input. I didn't have time to take a closer look yet, and this week I won't be available. But this PR is still on my to-do-list.
Btw, I updated the PR description to mention that the problem is related to using delegatePattern=true.