ctxUrl = sb.append(req.getScheme()).append("://")
.append(req.getgetServerName()).append(":")
.append(req.getServerPort()) etc

ctxUrl = req.getRequestURL();
ctxUrl = ctxUrl.substring(0, ctxUrl.lastIndexOf("/")));

StringBuffer url = req.getRequestURL();
String uri = req.getRequestURI();
String ctx = req.getContextPath();
String base = url.substring(0, url.length() - uri.length() + ctx.length()) + "/";

URI contextUrl = URI.create(req.getRequestURL().toString()).resolve(req.getContextPath());