Issues with POST Request, application/x-www-form-urlencoded and only one parameter

[mum-viadee]

Describe the bug
I have a REST API with Spring MVC. One REST controller has a method with only one parameter. It has a PostMapping with consumes set to "application/x-www-form-urlencoded". The generated openapi definition says, that the request body is of type String and directly contains the value of the parameter, in my case a UUID. There is no key-value pair like i had expected. If I use the button "Try it out" in the Swagger UI I get a bad request response.

[org.springframework.web.bind.MissingServletRequestParameterException: Required request parameter 'test_id' for method parameter type UUID is not present]

Steps to reproduce the behavior

• spring-boot 3.4.5
• springdoc-openapi-starter-webmvc-ui 2.8.8 (2.8.6)

Code-Example

@RestController
@Validated
public class DemoController {

    @PostMapping(path = "/api/test", consumes = MediaType.APPLICATION_FORM_URLENCODED_VALUE)
    public Result postSingleParameter(@RequestParam(name = "test_id") @NotNull final UUID testId) {
        return new Result("Test", "Just a simple test.");
    }

}

Actual Result:

"requestBody": {
          "content": {
            "application/x-www-form-urlencoded": {
              "schema": {
                "type": "string",
                "format": "uuid"
              }
            }
          },

Expected Result:

"requestBody": {
          "content": {
            "application/x-www-form-urlencoded": {
              "schema": {
                "type": "object",
                "properties": {
                  "test_id": {
                    "type": "string",
                    "format": "uuid"
                  }
                },
                "required": [
                  "test_id"
                ]
              }
            }
          },

[Mattias-Sehlstedt]

Hi @mum-viadee,

This looks to be an issue in swagger-core,

I have create a branch where I tested their introspection for a single primitive parameter

@POST
@Path("/search-id")
@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
public Response searchForThing(@BeanParam String id) {
    return Response.status(200).entity("Searching for something").build();
}

and it fails as

which is your reported issue.

[Mattias-Sehlstedt]

I saw that I used the incorrect parameter annotation (@BeanParam rather than @FormParam) and with the correction swagger-core seems to behave as expected. So more investigation is necessary.

Most likely a corner case that hasn't been covered here?