Twitter对象始终为null我从twitter4j中获取了示例

Question

protected void doGet（HttpServletRequest请求，HttpServletResponse响应）抛出ServletException，IOException     {

    TwitterFactory twitterFac = new TwitterFactory();
    Twitter twitter = twitterFac.getInstance();
    twitter.setOAuthConsumer("key", "secret");
    request.getSession().setAttribute("twitter", twitter);
    try
    {
        RequestToken requestToken = twitter.getOAuthRequestToken("http://local.your-domain.com:8080/sign-in-with-twitter/callback");
        request.getSession().setAttribute("requestToken", requestToken);
        System.out.println(requestToken.getAuthenticationURL());
        response.sendRedirect(requestToken.getAuthenticationURL());
    } catch (TwitterException e)
    {
        throw new ServletException(e);
    }

}

}

****然后Twitter页面重定向到我的应用程序页面（CallbackServlet）。所有这些都是正确执行的。****

然后CallbackServlet具有以下doGet方法：

public class CallbackServlet扩展HttpServlet {     private static final long serialVersionUID = 1657390011452788111L;

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    Twitter twitter = (Twitter) request.getSession().getAttribute("twitter");
    RequestToken requestToken = (RequestToken) request.getSession().getAttribute("oauth_token");
    String verifier = request.getParameter("oauth_verifier");
    try {
        twitter.getOAuthAccessToken(requestToken, verifier);
        request.getSession().removeAttribute("requestToken");
    } catch (TwitterException e) {
        throw new ServletException(e);
    }
    response.sendRedirect(request.getContextPath() + "/");
}

}

============================= CallbackServlet尝试将login和requestToken保存在LoginServlet中（使用方法getSession（）。getAttribute（））。这就是问题所在：twitter对象总是为空！

plz排序