code: protected String getEmbeddedId(
              final HttpServletRequest servletRequest, final Prefix prefix) {
          String requestPath = servletRequest.getPathInfo();
  
          // http://stackoverflow.com/questions/18963562/grizzlys-request-getpathinfo-returns-always-null
          if (requestPath == null && servletRequest.getContextPath().isEmpty()) {
              requestPath = servletRequest.getRequestURI();
          }
  
          String id = null;
          if (requestPath != null) {
              final String pathPrefix = prefix.getPrefix();
              final String[] part = requestPath.split("/");
              if (part.length > 1 && part[1].startsWith(pathPrefix)) {
                  id = part[1].substring(pathPrefix.length());
              }
          }
          return id;
      }
docs: Extract the id embedded at the beginning of a request path
  
  @param servletRequest the servlet request
  @param prefix the prefix for the id
  @return the found id or null