Error handling in typesafe clients

System-level errors

If the service returns a system-level error (which means the response body doesn't contain a valid GraphQL response document), the client invocation will throw a io.smallrye.graphql.client.InvalidResponseException whose message contains information about the received status code, status message, and body contents.

Application-level errors

If the service returns one or more application-level errors (which means that there is valid GraphQL response in the body that has a non-empty errors entry), the client normally throws a GraphQLClientException containing the details in a list of GraphQLClientError.

[NOTE] An error response is considered application-level regardless of the HTTP status code as long as it contains a valid GraphQL response. We define a GraphQL response as a well-formed JSON document that contains at least one of errors, data and extensions entries, and no other entries beyond that.

If the error is specific to a location, you can use an ErrorOr wrapper on the target field; the client the maps the error to that wrapper instead of throwing an exception. I.e. your SuperHero class could look like this:

class SuperHero {
    String name;
    ErrorOr<Location> location;
}

If the service returns a response like this:

{
  "data": {
    "superHero": {
      "name": "Wolverine",
      "location": null
    }
  },
  "errors": [{
    "message":"location unknown",
    "path": ["superHero","location"],
    "extensions":{"code":"location-unknown"}
  }]
}

Then the SuperHero#location wrapper field will not contain a value but only the error above. See the ErrorOr class for details.