Add awsGeneratedTags field to S3Bucket in s3-event-notifications

[ylyu-eng]

Motivation and Context

Amazon S3 event notifications delivered to SNS, SQS, and Lambda will include a new awsGeneratedTags map on the bucket object when system tags are enabled on the source bucket. The Java SDK model did not round-trip this field, so consumers had to fall back to raw JSON parsing to read the tags. This PR adds first-class support for the field on both the reader and writer sides.

Related: SIM P459766202 (internal launch coordination).

Note to reviewers: This PR targets master for review only. The intent is to retarget to a feature branch once the AWS Java SDK team creates one, and merge on launch day (7/15/2026).

Modifications

• S3Bucket: new Map<String, String> awsGeneratedTags field with getter, a new four-argument constructor, and updates to equals/hashCode/toString. The pre-existing three-argument constructor is preserved so existing callers are source- and behavior-compatible. Tags are defensively copied on construction and returned as an unmodifiable view..
• DefaultS3EventNotificationReader: parses awsGeneratedTags as Map<String, String> using a LinkedHashMap (preserves S3 emission order). Absent field yields null. Null value entries are preserved. Non-string values throw IllegalArgumentException with a helpful message including the offending key and value.
• DefaultS3EventNotificationWriter: emits awsGeneratedTags only when the map is non-null and non-empty, matching S3 server-side @JsonInclude(NON_EMPTY) behavior so round-tripped output is indistinguishable from what S3 emits.
• Bumps eventVersion fixtures in the module test files from 2.4 to 2.5 to reflect the schema version emitted alongside this launch.

Testing

Added tests in three files:

• S3BucketTest (new): S3BucketTest (new): 3-arg and 4-arg constructor defaults, toString behavior (omit-when-null, include-when-present with key/value assertions across multiple tags), defensive-copy of the tag map, and unmodifiable view via the getter.
• S3EventNotificationReaderTest: parse when present, absent, empty; null value preserved; empty string preserved; non-string value throws; boolean value throws; non-object throws.
• S3EventNotificationWriterTest: written when set (with round-trip); omitted when null; omitted when empty; null tag value preserved (round-trip); empty-string tag value preserved (round-trip).

Local run of ./mvnw test -pl :s3-event-notifications passes with 39 tests, 0 failures.

Screenshots (if appropriate)

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING document
• Local run of mvn install succeeds (module-level tests pass)
• My code follows the code style of this project
• My change requires a change to the Javadoc documentation
• I have updated the Javadoc documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed
• I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.

License

• I confirm that this pull request can be released under the Apache 2 license

[alextwoods]

Overall looking good!

This also needs a change log - you can create one with ./scripts/new-change