Marshalling & Unmarshalling
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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 a 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.completeAs or by using the BasicDirectives.completeAs 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 Marshallers.toEntityString, Marshallers.toEntityBytes, Marshallers.toEntityByteString, Marshallers.toEntity, and Marshallers.toResponse to create custom marshallers.

Unmarshalling

On the server-side unmarshalling is used to convert a request (entity) to a application-domain object. This means unmarshalling to a certain type is represented by a RequestVal. Currently, several options are provided to create an unmarshalling RequestVal:

  • Use Json Support via Jackson to create an unmarshaller that can convert an application/json request to a POJO using jackson.
  • Use the predefined Unmarshallers.String, Unmarshallers.ByteString, Unmarshallers.ByteArray, Unmarshallers.CharArray to convert to those basic types.
  • Use Unmarshallers.fromMessage or Unmarshaller.fromEntity to create a custom unmarshaller.

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