Swagger..Unable to render this definition The provided definition does not specify a valid version field

Question

Unable to render this definition The provided definition does not specify a valid version field.

Please indicate a valid Swagger or OpenAPI version field. Supported version fields are swagger: "2.0" and those that match openapi: 3.0.n (for example, openapi: 3.0.0).

Where do I need to insert the correct version to the stop the error below. Swagger editor works ok, but when launching a particular project I receive this error.First time using Swagger. Many Thanks

Answer 1

Your API definition is missing the OpenAPI/Swagger version number, in this case "swagger": "2.0". Add it at the beginning, like so:

{     "swagger": "2.0",      "title" : "Music API Documentation",     ... 

Answer 2

I encountered this same problem today. In my case it is the Gson configuration which lead to the error. If you are also using Gson with SpringMVC, may be you could try this out:

I am setting up a rest-api project using spring boot 2.2.4 and spring fox swagger 2.9.2 . Since I am more familiar with Gson than Jackson, I replaced the default MessageConverter:

@Configuration @EnableWebMvc public class MvcConfiguration implements WebMvcConfigurer {      private final Gson gson = new Gson();      // ......      @Override     public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {         GsonHttpMessageConverter gsonHttpMessageConverter = new GsonHttpMessageConverter();         gsonHttpMessageConverter.setGson(gson);         converters.add(gsonHttpMessageConverter);     }      // ......  } 

After that the "http://localhost:8080/swagger-ui.html" breaks like the question described. Then I typed "http://localhost:8080/v2/api-docs" in browser and noticed the swagger doc was wrapped into another layer, with an unnecessary "value" field like this:

{     value: "{"swagger":"2.0","info":{"description": ......}}" } 

No doubt swagger cannot find the "swagger":"2.0" field if api-docs yields something like that. The value of "value" field is the actual swagger doc.

After some search I found that swagger doc will be incorrectly serialized by Gson if you leave it be. The solution is simple - register a serializer for swagger to your Gson bean:

private final Gson gson = new GsonBuilder()         .registerTypeAdapter(Json.class, new SpringfoxJsonToGsonAdapter())         .create();  private static class SpringfoxJsonToGsonAdapter implements JsonSerializer<Json> {     @Override     public JsonElement serialize(Json json, Type type, JsonSerializationContext context) {         final JsonParser parser = new JsonParser();         return parser.parse(json.value());     } }  

where Json is a class provided by springfox:

import springfox.documentation.spring.web.json.Json; 

Hope this would help.