code: @Nonnull
    @ReturnsMutableCopy
    public static HttpHeaderMap getResponseHeaderMap (@Nonnull final HttpServletResponse aHttpResponse)
    {
      ValueEnforcer.notNull (aHttpResponse, "HttpResponse");
  
      final HttpHeaderMap ret = new HttpHeaderMap ();
      for (final String sName : aHttpResponse.getHeaderNames ())
        for (final String sValue : aHttpResponse.getHeaders (sName))
          ret.addHeader (sName, sValue);
      return ret;
    }
docs: Get a complete response header map as a copy.
  
  @param aHttpResponse
  The source HTTP response. May not be <code>null</code>.
  @return Never <code>null</code>.
  @since 8.7.3