How to define Workflow method arguments and return values as Java interface or abstract class?

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1

I want to define Workflow method arguments and return values as Java interface so the API is generic (without using Java generic since I don’t know all implementations of the interface). Is this supported OOTB?

I understand the default JSON data converter doesn’t know how to de/serialize interface/abstract classes. Is the only way is to provide my own data converter? If yes, then it’s not “elegant” since I can only provide data converter once per Temporal workflow client which my app has only one, therefore, I have to “inspect” the payload type, i.e., having conditional which I don’t want to do and I don’t want one workflow client per workflow type.

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4

By default Temporal uses Jackson for serialization and deserialization of arguments. It looks like Jackson supports polymorphic deserialization. It needs to be configured, but DataConverter APIs allow such configuration.

I personally would not recommend going this route as RPC that passes around non value classes is too brittle for my taste.

5

I’ve successfully used Jackson’s polymorphic deserialisation without having to define a custom data converter. Just using the @JsonTypeInfo and JsonSubTypes annotations on my value objects. I can then define both Workflow methods and Activity methods to accept and return Interface types rather than concrete classes. Here is an example in Kotlin. I think there are other ways to define the subtypes with Jackson annotations but this is the way that I knew how to do with Jackson.

@JsonTypeInfo(
  use = Id.NAME,
  include = As.Property,
  property = "@type"
)
@JsonSubTypes(
  JsonSubTypes.Type(value = First::class, name = "first"),
  JsonSubTypes.Type(value = Second::class, name = "second")
)
interface CustomInterface

data class First(
  @JsonProperty val first: String
) : CustomInterface

data class Second(
  @JsonProperty val second: Long
) : CustomInterface

The JSON payloads you’ll get for these will look like

{
  "@type": "first",
  "first": "this is a value"
}

{
  "@type": "second",
  "second": 123456789
}
1 Like
6

Thanks Tucker. Let me explore this approach.