OpenAPI Extensions no longer work. Fixes #2104

Author: bnasslahsen

springdoc-openapi-starter-common/src/main/java/org/springdoc/core/service/OpenAPIService.java

@@ -42,6 +42,7 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import com.fasterxml.jackson.annotation.JsonInclude.Include;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import io.swagger.v3.core.jackson.TypeNameResolver;
@@ -245,6 +246,9 @@ public OpenAPI build(Locale locale) {
 			try {
 				ObjectMapper objectMapper = ObjectMapperProvider.createJson(springDocConfigProperties);
 				calculatedOpenAPI = objectMapper.readValue(objectMapper.writeValueAsString(openAPI), OpenAPI.class);
+				objectMapper.setSerializationInclusion(Include.NON_EMPTY);
+				Map extensionsClone = objectMapper.readValue(objectMapper.writeValueAsString(openAPI.getExtensions()), Map.class);
+				calculatedOpenAPI.extensions(extensionsClone);
 			}
 			catch (JsonProcessingException e) {
 				LOGGER.warn("Json Processing Exception occurred: {}", e.getMessage());

springdoc-openapi-starter-webmvc-api/src/test/java/test/org/springdoc/api/v30/app173/SpringDocApp173Test.java

@@ -25,6 +25,7 @@
 package test.org.springdoc.api.v30.app173;
 
 import java.util.Locale;
+import java.util.Map;
 
 import io.swagger.v3.oas.models.OpenAPI;
 import org.junit.jupiter.api.Test;
@@ -67,7 +68,7 @@ private void testApp(Locale locale) throws Exception {
 	static class SpringDocTestApp {
 		@Bean
 		public OpenAPI openAPI() {
-			return new OpenAPI();
+			return new OpenAPI().extensions(Map.of("TEST", "HELLO"));
 		}
 	}
 

springdoc-openapi-starter-webmvc-api/src/test/resources/results/3.0.1/app173.json

@@ -25,5 +25,6 @@
       }
     }
   },
-  "components": {}
+  "components": {},
+  "TEST": "HELLO"
 }