Marshalling & Unmarshalling

“Marshalling” is the process of converting a higher-level (object) structure into some kind of lower-level representation (and vice versa), often a binary wire format. Other popular names for it are “Serialization” or “Pickling”.

In akka-http “Marshalling” means the conversion of an object of type T into an HttpEntity, which forms the entity body of an HTTP request or response (depending on whether used on the client or server side).

Marshalling

On the server-side marshalling is used to convert an application-domain object to a response (entity). Requests can contain an Accept header that lists acceptable content types for the client. A marshaller contains the logic to negotiate the result content types based on the Accept and the AcceptCharset headers.

Marshallers can be specified when completing a request with RequestContext.complete or by using one of the RouteDirectives.complete directives.

These marshallers are provided by akka-http:

  • Use Json Support via Jackson to create an marshaller that can convert a POJO to an application/json response using jackson.
  • Use Marshaller.stringToEntity, Marshaller.byteArrayToEntity, Marshaller.byteStringToEntity, combined with Marshaller.entityToResponse to create custom marshallers.

Unmarshalling

On the server-side unmarshalling is used to convert a request (entity) to an application-domain object. This is done in the MarshallingDirectives.request or MarshallingDirectives.entity directive. There are several unmarshallers provided by akka-http:

  • Use Json Support via Jackson to create an unmarshaller that can convert an application/json request to a POJO using jackson.
  • Use the predefined Unmarshaller.entityToString, Unmarshaller.entityToByteString, Unmarshaller.entityToByteArray, Unmarshaller.entityToCharArray to convert to those basic types.
  • Use Unmarshaller.sync or Unmarshaller.async to create a custom unmarshaller.