spring security插件--获取 登录前被拦截的URL

在web项目中，登录某些页面 需要登录权限，有些是由插件拦截，有的是自己手动写的判断代码在spring securrity中，会有映射的权限访问URL，如果在没有登录情况下 访问这些URL会被插件拦截器自动拦截，那么怎样获取当前被拦截的URL，用来实现跳转？1.一般实现  登录前的跳转---将登录前访问的URL放入session，登录成功后取出该URL，再删除改属性     

request.getHeader("referer")//获取登录访问前的URL

2.如果是spring security等安全插件拦截的URL，该如何获取被拦截的URL？

-----这里以AJAX请求登录为例

public class AjaxAwareAuthenticationEntryPoint extends LoginUrlAuthenticationEntryPoint {

private String ajaxLoginFormUrl;

@Override
protected String determineUrlToUseForThisRequest(final HttpServletRequest request,
final HttpServletResponse response, final AuthenticationException e) {

if (ajaxLoginFormUrl != null && SpringSecurityUtils.isAjax(request)) {
return ajaxLoginFormUrl;
}
try{
//设置  session属性--登录成功后要 要跳转的URL
request.getSession().setAttribute("back",buildHttpReturnUrlForRequest(request));
}catch(Exception ex){

}

return getLoginFormUrl();
}
//获取 当前被 （登录前）被拦截的URL
protected String buildHttpReturnUrlForRequest(HttpServletRequest request)
throws IOException, ServletException {
RedirectUrlBuilder urlBuilder = new RedirectUrlBuilder();
urlBuilder.setScheme("http");
urlBuilder.setServerName(request.getServerName());
urlBuilder.setPort(request.getServerPort());
urlBuilder.setContextPath(request.getContextPath());
urlBuilder.setServletPath(request.getServletPath());
urlBuilder.setPathInfo(request.getPathInfo());
urlBuilder.setQuery(request.getQueryString());

return urlBuilder.getUrl();
}
/**
* Dependency injection for the Ajax login form url, e.g. '/login/authAjax'.
* @param url  the url
*/
public void setAjaxLoginFormUrl(final String url) {
Assert.isTrue(url == null || url.startsWith("/"), "ajaxLoginFormUrl must begin with '/'");
ajaxLoginFormUrl = url;
}
}