private List<T> unmarshallResponseHeaderToList(
            JsonUnmarshallerContext context) throws Exception {

        String headerValue = context.readText();

        List<T> list = new ArrayList<T>();

        String[] headerValues = headerValue.split("[,]");

        for (final String headerVal : headerValues) {
            list.add(itemUnmarshaller.unmarshall(new JsonUnmarshallerContext() {
                @Override
                public String readText() {
                    return headerVal;
                }
            }));
        }
        return list;
    }
Un marshalls the response header into the list.
aws-java-sdk-core/src/main/java/com/amazonaws/transform/ListUnmarshaller.java