public Date unmarshall(JsonUnmarshallerContext unmarshallerContext)
                throws Exception {
            // If value is string, assume ISO8601. Otherwise parse as epoch seconds.
            if (unmarshallerContext.getCurrentToken() == JsonToken.VALUE_STRING) {
                return DateUtils.parseISO8601Date(unmarshallerContext.readText());
            } else {
                return DateUtils.parseServiceSpecificDate(unmarshallerContext.readText());
            }
        }
Unmarshaller for Date values - JSON dates come in as epoch seconds for AWS services and ISO8601 string
for API Gateway fronted services..
aws-java-sdk-core/src/main/java/com/amazonaws/transform/SimpleTypeJsonUnmarshallers.java