public String getExpiration() {
        return expiration;
    }
If the object expiration is configured (see PUT Bucket lifecycle), the response includes this header. It
includes the expiry-date and rule-id key-value pairs providing object expiration information. The value of
the rule-id is URL encoded.
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/model/WriteGetObjectResponseRequest.java