private static MediaType createConstantUtf8(String type, String subtype) {
        MediaType mediaType = addKnownType(new MediaType(type, subtype, UTF_8_CONSTANT_PARAMETERS));
        mediaType.parsedCharset = UTF_8;
        return mediaType;
    }
Matcher for type, subtype and attributes.
core/src/main/java/com/linecorp/armeria/common/MediaType.java