Not sure if this is the right forum for this, but I've come across a need for this pattern a few times lately, and I would love to get some opinions on options for how to handle it.

Say I have an app that takes data from an arbitrary number of third-party applications and wants to parse it into a unifying format:

    "field_1": "value_1",
    "field_2": "value_2"

So I might have integration 1 return a response that looks like

    "different_field_1_name": "desired_field_1_value",
    "field_2": "desired_field_2_value"

And integration 2 return a response that looks like

    "different_field_1_name_again": "desired_field_1_value",
    "different_field_2_name": "desired_field_2_value",
    "unneeded_field": "unneeded_value"


Ideally, adding new integrations should be as painless as possible. But every time I've had to do something like this, things like authentication, response formats, weird API quirks, etc. always make it feel like I'm starting from scratch with new integrations. Does anybody have examples of open-source applications that I can look at that do this sort of thing well? Or is there an obvious pattern I'm missing here that makes this easier?


1 Answer 1


Have a look at the adapter pattern (I'm guessing probably already know it). It is basically just a glorified mapper function:

DomainObject toDomain(ThirdPartyObject object) { ... } 

What you then need to do is just fetch the third party data. How that looks really depends on the provider and I don't think you can abstract it more than just:

List<ThirdPartyObject> fetch() { ... }

so basically you can create:

public abstract class IntegrationAdapter<T> {
  publict List<DomainObject> adapt() {
    List<T> thirdPartyObjects = fetch();
    return thirdPartyObjects.stream.map(this::toDomain).toList()

  private abstract List<T> fetch();
  private abstract DomainObject toDomain(T object);

You can then make implementations of this abstract class.

Or to have a more modular and easier to test components you could do:

public interface Client<T> {
  List<T> fetch();
public interface Mapper<D, T> {
  D toDomain(T object);
public interface DomainObjectRepository {
  List<DomainObject> getDomainObjects();
class ThirdPartyClient implements Client<ThirdPartyObject> { ... }
class DoTpoMapper implements Mapper<DomainObject, ThirdPartyObject> { ... }
class ThirdPartyRepository implements DomainObjectRepository {
  public ThirdPartyRepository(ThirdPartyClient, DoTpoMapper) {...}

  List<DomainObject> getDomainObjects() {
    List<T> thirdPartyObjects = this.thirdPartyClientfetch();
    return thirdPartyObjects.stream.map(doTpoMapper::toDomain).toList();

You can then write integration and unit tests for the client, the repository and the mapper, which you would write just once in a generic fashion, and could then reuse them when creating new adapters.

  • Yeah, this is pretty similar to what I was trying to do. I think I might just be bad at it haha. That's why I was hoping somebody had an example of it being done really well that I could look through. Jun 12, 2021 at 15:54
  • I am almost 100% sure that there is not much more to it. It is nice if the provider has some client in your language already setup, so you don't have to make your own, but it always is a lot of manual work making sure, that you fetch what you want and that you map all of the fields you want to map in the correct format. I guess you can test that pretty easily -> testing fetch() is an integration test and toDomain() can be a unit test. You would however have to split the adapter I showed into 3 classes - IntegrationAdapter, <Provider>Client and <Provider><DomainObject>Mapper
    – Blaž Mrak
    Jun 12, 2021 at 16:03
  • Actually you would have to create Client<T> and Mapper<T> interfaces before. I'll edit my answer with the code.
    – Blaž Mrak
    Jun 12, 2021 at 16:06

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