public Map<String, List<String>> getAllHttpHeaders() {
        return allHeaders;
    }
Returns all the headers sent in a response. Unlike
{@link #getHttpHeaders()}, this returns all the values given for a
field-name, rather than the last seen value.

@return All the headers returned in a response.
aws-java-sdk-core/src/main/java/com/amazonaws/http/SdkHttpMetadata.java