Avoid unnecessary async handling in GraphQlHttpHandler

In the webmvc GraphQlHttpHandler, return the server response directly if the
WebGraphQlHandler returns an already completed Mono. This avoids some extra
overhead incurred with async processing.

Author: kilink

spring-graphql/src/main/java/org/springframework/graphql/server/webmvc/GraphQlHttpHandler.java

@@ -106,8 +106,12 @@ public ServerResponse handleRequest(ServerRequest serverRequest) throws ServletE
 					builder.headers(headers -> headers.putAll(response.getResponseHeaders()));
 					builder.contentType(selectResponseMediaType(serverRequest));
 					return builder.body(response.toMap());
-				});
+				})
+				.cache();
 
+		if (responseMono.hasElement().block()) {
+			return responseMono.block();
+		}
 		return ServerResponse.async(responseMono);
 	}
 
@@ -138,5 +142,4 @@ private static MediaType selectResponseMediaType(ServerRequest serverRequest) {
 		}
 		return MediaType.APPLICATION_JSON;
 	}
-
 }

spring-graphql/src/test/java/org/springframework/graphql/server/webmvc/GraphQlHttpHandlerTests.java

@@ -122,7 +122,10 @@ private MockHttpServletResponse handleRequest(
 			MockHttpServletRequest servletRequest, GraphQlHttpHandler handler) throws ServletException, IOException {
 
 		ServerRequest request = ServerRequest.create(servletRequest, MESSAGE_READERS);
-		ServerResponse response = ((AsyncServerResponse) handler.handleRequest(request)).block();
+		ServerResponse response = handler.handleRequest(request);
+		if (response instanceof AsyncServerResponse asyncServerResponse) {
+			asyncServerResponse.block();
+		}
 
 		MockHttpServletResponse servletResponse = new MockHttpServletResponse();
 		response.writeTo(servletRequest, servletResponse, new DefaultContext());