Removal of JAXB annotations

[jeandersonbc]

Description

Removal the JAXB-bind related annotations. This change is needed due to Jakarta EE +9 compatibility.
In addition, we Improved type safety for AuthenticatedData.keyTransportOrKEK deserialization**:

Previously, items in the keyTransportOrKEK list were deserialized as raw Object (a Gson LinkedTreeMap at runtime), requiring brittle map access to read fields. The TerminalAPIGsonBuilder now registers a custom adapter that detects the concrete type of each list item at deserialization time — objects containing a KEKIdentifier field are deserialized as KEK, all others as KeyTransport. This makes safe casting possible:

 // After
 AuthenticatedData data = gson.fromJson(json, AuthenticatedData.class);

 // Cast to KEK
 KEK kek = (KEK) data.getKeyTransportOrKEK().get(0);
 String keyId = kek.getKEKIdentifier().getKeyIdentifier();

 // Cast to KeyTransport
 KeyTransport kt = (KeyTransport) data.getKeyTransportOrKEK().get(0);
 RecipientIdentifier recipient = kt.getRecipientIdentifier();

Further details:

Since the underlying serializer relies on Gson lib, we are unable to use directly Jackson annotations since they don't work as expected. This was verified via test coverage. Furthermore, the required=true validation was never enforced (see AbortRequestTest tests).

The existing code in com.adyen.terminal.serialization relies on GSON; thus,the JAXB annotations were replaced by the GSON's @SerializedName.

The migration was guided by test coverage and focused on serialization and deserialization of JSON payloads.

POM XML changes:

• removal of jaxb dependency
• addition of plugin enforcement to block unwanted dependencies

Tested scenarios

• Serialization/Deserialization from external file
• Missing required fields (that are not enforced in practice)

[gemini-code-assist]

Code Review

This pull request migrates several Nexo model classes, including AbortRequest, DisplayRequest, LoginRequest, and MessageHeader, from JAXB XML annotations to GSON @SerializedName annotations. The changes also involve removing JAXB-specific metadata and adding unit tests to verify that serialization and deserialization remain functional even when fields previously marked as required are missing from the JSON payload. I have no feedback to provide.

[thomas-cools]

@jeandersonbc is my understanding correct that we were using the jaxb annotation with GSON as the serializer / deserializer, so there is no actual change in behavior other than using GSON annotations?

[jeandersonbc]

@jeandersonbc is my understanding correct that we were using the jaxb annotation with GSON as the serializer / deserializer, so there is no actual change in behavior other than using GSON annotations?

Correct @thomas-cools (cc @gcatanese)! I also pushed this test that verifies how GSON handles the JAXB annotations. The target class (EventNotification) has not been migrated and has some required=true fields. If those checks were really enforced, EventNotificationTest would have failed.

I'm going to proceed to JAXB -> Gson annontations as part of the original task.

[gcatanese]

Great work Jean, this is a challenging issue.

I left few comments in the code and there is here one about test coverage, they might be edge cases so please assess whether they are applicable or not

Test Coverage Gaps

• No direct unit tests for XMLEnumTypeAdapter with @SerializedName, especially the edge case where the annotation is absent on an enum constant.
• No round-trip tests for SaleToPOIRequest — only SaleToPOIResponse is covered despite the same migration pattern.
• RepeatedMessageResponseBody / RepeatedResponseMessageBody — migrated but zero test coverage.
• TerminalAPIGsonBuilder fallback behavior — no test verifying the behavior when @SerializedName is missing.