Retrieve value of 'contentWritten' from 'HttpServletResponse' Object

Question

I have a function which have 'HttpServletResponse' object named 'lResponse'. I want to get the size of the Http Response. I want to retrieve a value of attribute 'contentWritten' from that object (lResponse object) so that I will save it in the 'responseSize' variable and pass it to the next function. The current code/function is like this.

private void filterPublicRequest(HttpServletRequest lRequest, HttpServletResponse lResponse, DbRouteMonitor dbRouteMonitor, FilterChain pFilterChain) throws IOException, ServletException {
    if (lRequest.getRequestURI().contains(API_ROUTE) && ConfigHelper.isMonitorEnabled()) {
        int id = dbRouteMonitorService.addMonitorData(dbRouteMonitor);
        pFilterChain.doFilter(lRequest, lResponse);
        String responseSize =  "";
        //code here to get response size from 'lResponse' Object and pass to 'updateResponseData' function.

        dbRouteMonitorService.updateResponseData(id, lResponse.getStatus(), responseSize);
    } else {
        pFilterChain.doFilter(lRequest, lResponse);
    }
}

When I debug this code I am getting value of 'contentWritten' attribute in the 'HttpServletResponse' Object (for example here that value of 'contentWritten' is 445872). I want to assign it to the variable 'responseSize'. Please have look at below snapshot.

How could I get the value of the attribute 'contentWritten' from the 'HttpResponseObject'?

Thanks in advance.