[spring] reactive: fix Content-Type (#16228)

* don't set content-type to client's value

* revert manual sample change

* better fix

* generate samples

* cover 3rd case

* add new test endpoint

samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/api/FakeApi.java

@@ -578,6 +578,44 @@ public interface FakeApi {
     }
 
 
+    /**
+     * GET /fake/response-with-example
+     * This endpoint defines an example value for its response schema.
+     *
+     * @return Success (status code 200)
+     */
+    @ApiOperation(
+        tags = { "fake" },
+        value = "",
+        nickname = "testWithResultExample",
+        notes = "This endpoint defines an example value for its response schema.",
+        response = Integer.class
+    )
+    @ApiResponses({
+        @ApiResponse(code = 200, message = "Success", response = Integer.class)
+    })
+    @RequestMapping(
+        method = RequestMethod.GET,
+        value = "/fake/response-with-example",
+        produces = { "application/json" }
+    )
+    default ResponseEntity<Integer> testWithResultExample(
+        
+    ) {
+        getRequest().ifPresent(request -> {
+            for (MediaType mediaType: MediaType.parseMediaTypes(request.getHeader("Accept"))) {
+                if (mediaType.isCompatibleWith(MediaType.valueOf("application/json"))) {
+                    String exampleString = "42";
+                    ApiUtil.setExampleResponse(request, "application/json", exampleString);
+                    break;
+                }
+            }
+        });
+        return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);
+
+    }
+
+
     /**
      * POST /fake/{petId}/uploadImageWithRequiredFile : uploads an image (required)
      * 

samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/resources/openapi.yaml

@@ -1088,6 +1088,23 @@ paths:
       x-accepts: application/json
       x-tags:
       - tag: fake
+  /fake/response-with-example:
+    get:
+      description: This endpoint defines an example value for its response schema.
+      operationId: testWithResultExample
+      responses:
+        "200":
+          content:
+            application/json:
+              schema:
+                example: 42
+                type: integer
+          description: Success
+      tags:
+      - fake
+      x-accepts: application/json
+      x-tags:
+      - tag: fake
   /fake/test-query-parameters:
     put:
       description: To test the collection format in query parameters