gistfile1.java

    public static String getActionUrl(String itUrl,Action action) {
        String urlName = action.getUrlName();
        if(urlName==null)   return null;    // to avoid NPE and fail to render the whole page
        if(SCHEME.matcher(urlName).find())
            return urlName; // absolute URL
        if(urlName.startsWith("/"))
            return joinPath(Stapler.getCurrentRequest().getContextPath(),urlName);
        else
            // relative URL name
            return urlName;
    }