Not suitable for dynamic urls calculated for each request

Hello:
First, thank you very much for sharing your excellent work.

In my case, I need a proxy for which I get the full (complete) url through a service, like this: http://user:password@10.0.2.40/112/2015_04/file88d78d.mp3

For this case, your servlet does not work unless some methods are overridden, because you code assumes that targetUri and targetHost are fixed and initialized once.

Then my solution working:

    @Override
    public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException,
            IOException {
        log.trace("<== {}?{}",request.getRequestURL(),request.getQueryString());
        if (cat.verify(request.getQueryString())) {
            try {
                targetUriObj = new URI(sercomResources.getRecord(request.getParameter("id")).getUrl());
                targetHost = URIUtils.extractHost(targetUriObj);
                log.trace("==> {}",targetUriObj);
                super.service(request, response);
            } catch (Exception e) {
                log.warn("Error obteniendo destino",e);
                throw new ServletException("Trying to process targetUri init parameter: " + e, e);
            }
        } else {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, CAT.CESTEL_AUTH_TOKEN
                    + " missing.");
            log.warn("Intento de acceso prohibido: {}", request.getRequestURI());
        }
    }

    @Override
    protected void initTarget() throws ServletException {
        /**
         * evitar super.initTarget() porque, al no estabecer parámetros en la
         * inicialización, esta llamada genera NPE
         */
        // super.initTarget();
    }

    @Override
    protected String rewriteUrlFromRequest(HttpServletRequest servletRequest) {
        /**
         * super.rewriteUrlFromRequest(servletRequest) genera Url errónea
         */
        return targetUriObj.toString();
    }

Thanks again.
Regards.

Start by reading the servlet's initTarget and rewriteUrlFromRequest entry points and the request lifecycle around them. Define how a complete destination URL can be selected for each request without requiring subclass overrides, then verify that authenticated requests proxy to that destination while invalid requests still return an error.