private Map<String, List<String>> unmodifiableHeaders(Map<String, List<String>> allHeaders) {
        Map<String, List<String>> unmodifiable = new HashMap<String, List<String>>();
        for (Map.Entry<String, List<String>> e : allHeaders.entrySet()) {
            unmodifiable.put(e.getKey(), Collections.unmodifiableList(e.getValue()));
        }
        return Collections.unmodifiableMap(unmodifiable);
    }
Static factory to create an {@link SdkHttpMetadata} from the details in a {@link
HttpResponse}.
aws-java-sdk-core/src/main/java/com/amazonaws/http/SdkHttpMetadata.java