[BUG] [JAVA] [RESTCLIENT] [MAVEN] Maven plugin 7.22.0 produces invalid client code to get application/octet-stream

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

I have a simple OpenAPI specification (external openapi, I cannot change it):

paths:
  /download:
    get:
      summary: Download file
      operationId: downloadFile
      parameters:
        - name: fileName
          in: query
          description: File name
          required: true
          schema:
            type: string
      responses:
        "200":
          description: Success
          content:
            application/octet-stream:
              schema:
                type: string
                format: binary
        "4XX":
          description: Failure
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/errorResponse"

I generate code client with openapi-generator-maven-plugin 7.22.0 and try to download file via the generated client in my unit test:

  @Test
  void downloadProblem() {
    File ok = defaultApi.downloadFile("ok");
    assertThat(ok).exists();
  }

I expect the code downloads file successfully, but instead one failed with:

org.springframework.web.client.UnknownContentTypeException: Could not extract response: no suitable HttpMessageConverter found for response type [class java.io.File] and content type [application/octet-stream]

	at org.springframework.web.client.DefaultRestClient.readWithMessageConverters(DefaultRestClient.java:251)
	at org.springframework.web.client.DefaultRestClient$DefaultResponseSpec.readBody(DefaultRestClient.java:826)
	at org.springframework.web.client.DefaultRestClient$DefaultResponseSpec.lambda$body$1(DefaultRestClient.java:765)
	at org.springframework.web.client.DefaultRestClient$DefaultRequestBodyUriSpec.exchangeInternal(DefaultRestClient.java:586)
	at org.springframework.web.client.DefaultRestClient$DefaultRequestBodyUriSpec.exchange(DefaultRestClient.java:540)
	at org.springframework.web.client.RestClient$RequestHeadersSpec.exchange(RestClient.java:677)
	at org.springframework.web.client.DefaultRestClient$DefaultResponseSpec.executeAndExtract(DefaultRestClient.java:821)
	at org.springframework.web.client.DefaultRestClient$DefaultResponseSpec.body(DefaultRestClient.java:765)

openapi-generator version

7.22.0

OpenAPI declaration file content or url

https://github.com/anatoly-spb/openapi-octet-stream-problem/blob/main/src/main/resources/downloader.yaml

Generation Details

https://github.com/anatoly-spb/openapi-octet-stream-problem/blob/main/pom.xml#L109

Steps to reproduce

• clone project git clone https://github.com/anatoly-spb/openapi-octet-stream-problem.git
• run unit test with mvn test
• downloadProblem failed instead of success

Related issues/PRs

Suggest a fix

Clone the linked reproduction project and run the downloadProblem test with mvn test, using downloader.yaml and the generation settings in pom.xml as the starting points. Trace the generated Java REST client’s application/octet-stream handling and compare it with the expected File result; done means the test downloads the file successfully without UnknownContentTypeException.