Rever to "application/json" as default MIME type

As of #108, the `"application/graphql+json"` media type is supported and
has been made the default.

It seems that it is not ready for adoption now; so while we'll keep
supporting it, this commit reverts back to `"application/json"` as the
default media type for servers and clients.

Closes gh-375

spring-graphql-test/src/main/java/org/springframework/graphql/test/tester/WebTestClientTransport.java

@@ -55,12 +55,12 @@ final class WebTestClientTransport implements GraphQlTransport {
 	public Mono<GraphQlResponse> execute(GraphQlRequest request) {
 
 		Map<String, Object> responseMap = this.webTestClient.post()
-				.contentType(MediaType.APPLICATION_GRAPHQL)
-				.accept(MediaType.APPLICATION_GRAPHQL)
+				.contentType(MediaType.APPLICATION_JSON)
+				.accept(MediaType.APPLICATION_JSON)
 				.bodyValue(request.toMap())
 				.exchange()
 				.expectStatus().isOk()
-				.expectHeader().contentTypeCompatibleWith(MediaType.APPLICATION_GRAPHQL)
+				.expectHeader().contentTypeCompatibleWith(MediaType.APPLICATION_JSON)
 				.expectBody(MAP_TYPE)
 				.returnResult()
 				.getResponseBody();

spring-graphql/src/main/java/org/springframework/graphql/client/DefaultRSocketGraphQlClientBuilder.java

@@ -61,7 +61,7 @@ final class DefaultRSocketGraphQlClientBuilder
 	}
 
 	private static RSocketRequester.Builder initRSocketRequestBuilder() {
-		RSocketRequester.Builder requesterBuilder = RSocketRequester.builder().dataMimeType(MimeTypeUtils.APPLICATION_GRAPHQL);
+		RSocketRequester.Builder requesterBuilder = RSocketRequester.builder().dataMimeType(MimeTypeUtils.APPLICATION_JSON);
 		if (jackson2Present) {
 			requesterBuilder.rsocketStrategies(
 					RSocketStrategies.builder()

spring-graphql/src/main/java/org/springframework/graphql/client/HttpGraphQlTransport.java

@@ -60,15 +60,15 @@ private static MediaType initContentType(WebClient webClient) {
 		HttpHeaders headers = new HttpHeaders();
 		webClient.mutate().defaultHeaders(headers::putAll);
 		MediaType contentType = headers.getContentType();
-		return (contentType != null ? contentType : MediaType.APPLICATION_GRAPHQL);
+		return (contentType != null ? contentType : MediaType.APPLICATION_JSON);
 	}
 
 
 	@Override
 	public Mono<GraphQlResponse> execute(GraphQlRequest request) {
 		return this.webClient.post()
 				.contentType(this.contentType)
-				.accept(MediaType.APPLICATION_GRAPHQL, MediaType.APPLICATION_JSON)
+				.accept(MediaType.APPLICATION_JSON, MediaType.APPLICATION_GRAPHQL)
 				.bodyValue(request.toMap())
 				.retrieve()
 				.bodyToMono(MAP_TYPE)

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

@@ -94,7 +94,7 @@ private static MediaType selectResponseMediaType(ServerRequest serverRequest) {
 				return accepted;
 			}
 		}
-		return MediaType.APPLICATION_GRAPHQL;
+		return MediaType.APPLICATION_JSON;
 	}
 
 }

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

@@ -117,7 +117,7 @@ private static MediaType selectResponseMediaType(ServerRequest serverRequest) {
 				return accepted;
 			}
 		}
-		return MediaType.APPLICATION_GRAPHQL;
+		return MediaType.APPLICATION_JSON;
 	}
 
 }

spring-graphql/src/test/java/org/springframework/graphql/client/WebGraphQlClientBuilderTests.java

@@ -183,18 +183,18 @@ void contentTypeDefault() {
 		setup.initBuilder().build().document(DOCUMENT).execute().block(TIMEOUT);
 
 		WebGraphQlRequest request = setup.getActualRequest();
-		assertThat(request.getHeaders().getContentType()).isEqualTo(MediaType.APPLICATION_GRAPHQL);
+		assertThat(request.getHeaders().getContentType()).isEqualTo(MediaType.APPLICATION_JSON);
 	}
 
 	@Test
 	void contentTypeOverride() {
 
 		HttpBuilderSetup setup = new HttpBuilderSetup();
-		setup.initBuilder().header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE).build()
+		setup.initBuilder().header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_GRAPHQL_VALUE).build()
 				.document(DOCUMENT).execute().block(TIMEOUT);
 
 		WebGraphQlRequest request = setup.getActualRequest();
-		assertThat(request.getHeaders().getContentType()).isEqualTo(MediaType.APPLICATION_JSON);
+		assertThat(request.getHeaders().getContentType()).isEqualTo(MediaType.APPLICATION_GRAPHQL);
 
 	}
 

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

@@ -51,14 +51,14 @@ public class GraphQlHttpHandlerTests {
 
 
 	@Test
-	void shouldProduceApplicationGraphQlByDefault() {
+	void shouldProduceApplicationJsonByDefault() {
 		MockServerHttpRequest httpRequest = MockServerHttpRequest.post("/")
-				.contentType(MediaType.APPLICATION_GRAPHQL).accept(MediaType.ALL).build();
+				.contentType(MediaType.APPLICATION_JSON).accept(MediaType.ALL).build();
 
 		MockServerHttpResponse httpResponse = handleRequest(
 				httpRequest, this.greetingHandler, Collections.singletonMap("query", "{greeting}"));
 
-		assertThat(httpResponse.getHeaders().getContentType()).isEqualTo(MediaType.APPLICATION_GRAPHQL);
+		assertThat(httpResponse.getHeaders().getContentType()).isEqualTo(MediaType.APPLICATION_JSON);
 	}
 
 	@Test
@@ -75,7 +75,7 @@ void shouldProduceApplicationGraphQl() {
 	@Test
 	void shouldProduceApplicationJson() {
 		MockServerHttpRequest httpRequest = MockServerHttpRequest.post("/")
-				.contentType(MediaType.APPLICATION_GRAPHQL).accept(MediaType.APPLICATION_JSON).build();
+				.contentType(MediaType.APPLICATION_JSON).accept(MediaType.APPLICATION_JSON).build();
 
 		MockServerHttpResponse httpResponse = handleRequest(
 				httpRequest, this.greetingHandler, Collections.singletonMap("query", "{greeting}"));

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

@@ -56,10 +56,10 @@ public class GraphQlHttpHandlerTests {
 			.queryFetcher("greeting", (env) -> "Hello").toHttpHandler();
 
 	@Test
-	void shouldProduceApplicationGraphQlByDefault() throws Exception {
+	void shouldProduceApplicationJsonByDefault() throws Exception {
 		MockHttpServletRequest servletRequest = createServletRequest("{\"query\":\"{ greeting }\"}", "*/*");
 		MockHttpServletResponse servletResponse = handleRequest(servletRequest, this.greetingHandler);
-		assertThat(servletResponse.getContentType()).isEqualTo(MediaType.APPLICATION_GRAPHQL_VALUE);
+		assertThat(servletResponse.getContentType()).isEqualTo(MediaType.APPLICATION_JSON_VALUE);
 	}
 
 	@Test
@@ -111,7 +111,7 @@ void shouldSetExecutionId() throws Exception {
 
 	private MockHttpServletRequest createServletRequest(String query, String accept) {
 		MockHttpServletRequest servletRequest = new MockHttpServletRequest("POST", "/");
-		servletRequest.setContentType(MediaType.APPLICATION_GRAPHQL_VALUE);
+		servletRequest.setContentType(MediaType.APPLICATION_JSON_VALUE);
 		servletRequest.setContent(query.getBytes(StandardCharsets.UTF_8));
 		servletRequest.addHeader("Accept", accept);
 		servletRequest.setAsyncSupported(true);