How can I get the HTTP status code out of a ServletResponse in a ServletFilter?

Question

I'm trying to report on every HTTP status code returned from my webapp. However the status code does not appear to be accessible via the ServletResponse, or even if I cast it to a HttpServletResponse. Is there a way to get access to this value within a ServletFilter?

Answer 1

Write an HttpServletResponseWrapper and override all the setStatus(), sendError(), and sendRedirect() methods to log everything. Write a Filter that swaps your wrapper in for the response object on every request.

Answer 2

First, you need to save the status code in an accessible place. The best to wrap the response with your implementation and keep it there:

public class StatusExposingServletResponse extends HttpServletResponseWrapper {

    private int httpStatus;

    public StatusExposingServletResponse(HttpServletResponse response) {
        super(response);
    }

    @Override
    public void sendError(int sc) throws IOException {
        httpStatus = sc;
        super.sendError(sc);
    }

    @Override
    public void sendError(int sc, String msg) throws IOException {
        httpStatus = sc;
        super.sendError(sc, msg);
    }


    @Override
    public void setStatus(int sc) {
        httpStatus = sc;
        super.setStatus(sc);
    }

    public int getStatus() {
        return httpStatus;
    }

}

In order to use this wrapper, you need to add a servlet filter, were you can do your reporting:

public class StatusReportingFilter implements Filter {

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        StatusExposingServletResponse response = new StatusExposingServletResponse((HttpServletResponse)res);
        chain.doFilter(req, response);
        int status = response.getStatus();
        // report
    }

    public void init(FilterConfig config) throws ServletException {
        //empty
    }

    public void destroy() {
        // empty
    }

}

Answer 3

One thing missing from David's answer above is that you should also override the other form of sendError:

@Override
public void sendError(int sc, String msg) throws IOException {
    httpStatus = sc;
    super.sendError(sc, msg);
}