Register a new content type handler. If a handler for the same MIME type was already registered it is replaced.
Select the deserializer for an incoming Content-Type header.
Returns null if the content type is not recognised; the server will
respond with 415 Unsupported Media Type in that case.
OptionalcontentTypeHeader: stringSelect the best response serializer for the given Accept header value.
Returns null if no registered handler can satisfy the request;
the server will respond with 406 Not Acceptable in that case.
OptionalacceptHeader: string
Selects the appropriate serializer/deserializer for a request or response based on the
Accept/Content-TypeHTTP headers.JSON is registered by default. Additional handlers can be added with
register()or viaServerBuilder.contentType().