dirtyaffairs

    public static String getQueryStringParameter(
            String queryString, String parameterName) {

        String[] parametersArray = queryString.split("&");
        for (String parameter : parametersArray) {

            if (parameter.contains(parameterName + "=")) {

                return parameter.split("=")[1];
            }
        }
        return null;
    }

    public static String getSearchEngineQueryString(
            HttpServletRequest request) {

        String referer = request.getHeader("Referer");
        String queryString;
        String hostName;
        if (referer != null) {

            //Validate that Referer header value is a correct URL, a
            //MalformedURLException is thrown if not
            URL refererURL;
            try {
                refererURL = new URL(referer);
            } catch (MalformedURLException e) {
                return null;
            }

            hostName = refererURL.getHost();
            queryString = refererURL.getQuery();

            if (hostName.toLowerCase().contains("google")) {

                queryString = getQueryStringParameter(queryString, "q");

            } else if (hostName.toLowerCase().contains("yahoo")) {

                queryString = getQueryStringParameter(queryString, "p");

            } else if (hostName.toLowerCase().contains("bing")) {

                queryString = getQueryStringParameter(queryString, "q");

            } else {

                //Search engine not recognized
                return null;
            }
            return queryString;
        }
        //No Referer header found
        return null;
    }