Fix Jaxb2Marshaller when mtomEnabled and schema validation are both set

[arimu1]

Overview

When Jaxb2Marshaller has both mtomEnabled=true and a configured schema/schemas, marshalling fails with:

cvc-type.3.1.2: Element '…' is a simple type, so it must have no element information item [children].

XOP packaging replaces xs:base64Binary simple content with xop:Include element children. JAXB applies the Schema to the XOP-encoded stream, so validation rejects valid logical content.

Reported via spring-projects/spring-ws#1030 (SWS-958); sample: https://github.com/mpeterka/spring-ws-mtom (testMarshallMtom).

The bug lives in spring-oxm (Jaxb2Marshaller), not in Spring WS itself.

Fix

When MTOM is active and a schema is configured:

1. Validate the logical infoset first: marshall with schema, with a non-XOP AttachmentMarshaller (isXOPPackage() == false) so base64Binary stays simple content and @XmlAttachmentRef/SWA still get a placeholder content id.
2. MTOM-encode without schema: marshall with the real MimeContainer attachment marshaller so xop:Include is written without re-validating the XOP package.

This matches the expected order from the issue: validate → replace with MTOM includes → send.

Tests

• marshalAttachmentsWithSchema — MTOM + matching XSD succeeds and still adds attachments
• marshalAttachmentsWithSchemaRejectsInvalidGraph — wrong schema still fails before attachments are added
• Existing marshalAttachments unchanged

./gradlew :spring-oxm:test --tests org.springframework.oxm.jaxb.Jaxb2MarshallerTests \
  --tests org.springframework.oxm.jaxb.Jaxb2UnmarshallerTests

24 + 12 tests green (Temurin 25).

Related

• Fixes spring-projects/spring-ws#1030
• Does not change inbound unmarshalling + schema (still XOP-on-the-wire vs logical schema); server-side PayloadValidatingInterceptor can be a follow-up if needed.