@Override
    public Collection<String> getHeaderNames(HttpURLConnection response) {
        final Map<String, List<String>> headerFields = response.getHeaderFields();
        if (MapUtils.isEmpty(headerFields)) {
            return Collections.emptyList();
        }
        return headerFields.keySet();
    }
return the last header value if set
agent-module/plugins/jdk-http/src/main/java/com/navercorp/pinpoint/plugin/jdk/http/JdkHttpClientResponseAdaptor.java