Update of JSON media supports (helidon-io#11234)

* Update media supports
- consistent approach to analysis of media types
- consistent approach in handling charsets
- consistent approach in configuring supports
- added methods with `io.helidon.config.Conifg` and deprecated old ones
- now using service registry instead of service loader in GSON (backward compatible)
- media types are now validated against the `Accept` header of request (for server responses)
- content type and accepted types are now configurable for all JSON supports
- failure to parse charset now returns 415
- Use an explicit media support in metrics, to avoid problems when JSON-P support is not added by users.

As part of testing, I found out we have a lot of warnings for generated builders, as they use deprecated Config, added suppress warnings annotation.

Author: tomas-langer

builder/codegen/src/main/java/io/helidon/builder/codegen/BuilderCodegen.java

@@ -705,6 +705,8 @@ private void generatePrototype(RoundContext ctx,
                 .copyright(CodegenUtil.copyright(GENERATOR,
                                                  blueprint.typeName(),
                                                  prototype))
+                // adding suppress warnings for config - once we remove helidon-common-config, we can remove this
+                .addAnnotation(Annotation.create(SuppressWarnings.class, "removal"))
                 .accessModifier(prototypeInfo.accessModifier());
 
         typeArguments.forEach(classModel::addGenericArgument);

http/http/src/main/java/io/helidon/http/HeaderNames.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, 2025 Oracle and/or its affiliates.
+ * Copyright (c) 2023, 2026 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,12 +35,14 @@ public final class HeaderNames {
     public static final HeaderName ACCEPT = HeaderNameEnum.ACCEPT;
     /**
      * The {@value} header name.
-     * Character sets that are acceptedTypes.
+     * This header is no longer sent by browsers, and it should be ignored by servers.
+     * Character sets that are accepted.
      */
     public static final String ACCEPT_CHARSET_NAME = Strings.ACCEPT_CHARSET_NAME;
     /**
      * The {@value #ACCEPT_CHARSET_NAME} header name.
-     * Character sets that are acceptedTypes.
+     * This header is no longer sent by browsers, and it should be ignored by servers.
+     * Character sets that are accepted.
      */
     public static final HeaderName ACCEPT_CHARSET = HeaderNameEnum.ACCEPT_CHARSET;
     /**

http/http/src/main/java/io/helidon/http/HttpMediaTypes.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023 Oracle and/or its affiliates.
+ * Copyright (c) 2023, 2026 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -31,6 +31,14 @@ public final class HttpMediaTypes {
             .mediaType(MediaTypes.APPLICATION_JSON)
             .charset("UTF-8")
             .build();
+
+    /**
+     * application/json media type with no explicit charset.
+     */
+    public static final HttpMediaType JSON = HttpMediaType.builder()
+            .mediaType(MediaTypes.APPLICATION_JSON)
+            .build();
+
     /**
      * Predicate to test if {@link io.helidon.common.media.type.MediaType} is {@code application/json} or has {@code json} suffix.
      */

http/media/gson/pom.xml

@@ -42,6 +42,14 @@
             <groupId>io.helidon.common</groupId>
             <artifactId>helidon-common-config</artifactId>
         </dependency>
+        <dependency>
+            <groupId>io.helidon.common</groupId>
+            <artifactId>helidon-common-types</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.helidon.service</groupId>
+            <artifactId>helidon-service-registry</artifactId>
+        </dependency>
         <dependency>
             <groupId>io.helidon.config</groupId>
             <artifactId>helidon-config</artifactId>

http/media/gson/src/main/java/io/helidon/http/media/gson/GsonConfigSupport.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2026 Oracle and/or its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.helidon.http.media.gson;
+
+import java.util.Map;
+import java.util.function.Consumer;
+
+import io.helidon.builder.api.Prototype;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+
+final class GsonConfigSupport {
+    private GsonConfigSupport() {
+    }
+
+    static class Decorator implements Prototype.BuilderDecorator<GsonSupportConfig.BuilderBase<?, ?>> {
+        private static final Gson GSON = new GsonBuilder().create();
+        private static final Map<String, Consumer<GsonBuilder>> BOOLEAN_PROPERTIES;
+
+        static {
+            BOOLEAN_PROPERTIES = Map.of("pretty-printing",
+                                        GsonBuilder::setPrettyPrinting,
+                                        "disable-html-escaping",
+                                        GsonBuilder::disableHtmlEscaping,
+                                        "disable-inner-class-serialization",
+                                        GsonBuilder::disableInnerClassSerialization,
+                                        "disable-jdk-unsafe",
+                                        GsonBuilder::disableJdkUnsafe,
+                                        "enable-complex-map-key-serialization",
+                                        GsonBuilder::enableComplexMapKeySerialization,
+                                        "exclude-fields-without-expose-annotation",
+                                        GsonBuilder::excludeFieldsWithoutExposeAnnotation,
+                                        "generate-non-executable-json",
+                                        GsonBuilder::generateNonExecutableJson,
+                                        "serialize-special-floating-point-values",
+                                        GsonBuilder::serializeSpecialFloatingPointValues,
+                                        "lenient",
+                                        GsonBuilder::setLenient,
+                                        "serialize-nulls",
+                                        GsonBuilder::serializeNulls);
+        }
+
+        @Override
+        public void decorate(GsonSupportConfig.BuilderBase<?, ?> target) {
+            if (target.gson().isEmpty()) {
+                if (target.properties().isEmpty() && target.typeAdapterFactories().isEmpty()) {
+                    target.gson(GSON);
+                } else {
+                    GsonBuilder builder = new GsonBuilder();
+                    target.properties()
+                            .entrySet()
+                            .stream()
+                            .filter(Map.Entry::getValue)
+                            .filter(entry -> BOOLEAN_PROPERTIES.containsKey(entry.getKey()))
+                            .forEach(entry -> BOOLEAN_PROPERTIES.get(entry.getKey()).accept(builder));
+                    target.typeAdapterFactories()
+                            .forEach(builder::registerTypeAdapterFactory);
+                    target.gson(builder.create());
+                }
+            }
+        }
+    }
+}

http/media/gson/src/main/java/io/helidon/http/media/gson/GsonMediaSupportProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2025 Oracle and/or its affiliates.
+ * Copyright (c) 2025, 2026 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,7 +16,7 @@
 package io.helidon.http.media.gson;
 
 import io.helidon.common.Weighted;
-import io.helidon.common.config.Config;
+import io.helidon.config.Config;
 import io.helidon.http.media.MediaSupport;
 import io.helidon.http.media.spi.MediaSupportProvider;
 
@@ -35,12 +35,13 @@ public GsonMediaSupportProvider() {
 
     @Override
     public String configKey() {
-        return "gson";
+        return GsonSupport.ID;
     }
 
+    @SuppressWarnings("removal")
     @Override
-    public MediaSupport create(Config config, String name) {
-        return GsonSupport.create(config, name);
+    public MediaSupport create(io.helidon.common.config.Config config, String name) {
+        return GsonSupport.create(Config.config(config), name);
     }
 
     @Override

http/media/gson/src/main/java/io/helidon/http/media/gson/GsonReader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2025 Oracle and/or its affiliates.
+ * Copyright (c) 2025, 2026 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,20 +15,16 @@
  */
 package io.helidon.http.media.gson;
 
-
 import java.io.InputStream;
 import java.io.InputStreamReader;
-import java.nio.charset.Charset;
-import java.nio.charset.StandardCharsets;
 
 import io.helidon.common.GenericType;
 import io.helidon.http.Headers;
-import io.helidon.http.HttpMediaType;
-import io.helidon.http.media.EntityReader;
+import io.helidon.http.media.EntityReaderBase;
 
 import com.google.gson.Gson;
 
-class GsonReader<T> implements EntityReader<T> {
+class GsonReader<T> extends EntityReaderBase<T> {
     private final Gson gson;
 
     GsonReader(Gson gson) {
@@ -44,11 +40,4 @@ public T read(GenericType<T> type, InputStream stream, Headers headers) {
     public T read(GenericType<T> type, InputStream stream, Headers requestHeaders, Headers responseHeaders) {
         return gson.fromJson(new InputStreamReader(stream, contentTypeCharset(responseHeaders)), type.type());
     }
-
-    private Charset contentTypeCharset(Headers headers) {
-        return headers.contentType()
-                .flatMap(HttpMediaType::charset)
-                .map(Charset::forName)
-                .orElse(StandardCharsets.UTF_8);
-    }
 }