微信BAE+Servlet+JSP OAuth2.0网页授权Tomcat 500错误

问题如图
访问url能出现微信授权页面，后面跳转页面index.jsp就出现这种状况。Servlet api包也加了，怎么样解决？

public class OAuthServlet extends HttpServlet {
private static final long serialVersionUID = -1847238807216447030L;[/align][align=left] public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  request.setCharacterEncoding("gb2312");
  response.setCharacterEncoding("gb2312");[/align][align=left]  // 用户同意授权后，能获取到code
  String code = request.getParameter("code");[/align][align=left]  // 用户同意授权
  if (!"authdeny".equals(code)) {
   // 获取网页授权access_token
   WeixinOauth2Token weixinOauth2Token = AdvancedUtil.getOauth2AccessToken("APPID", "APPSECRET", code);
   // 网页授权接口访问凭证
   String accessToken = weixinOauth2Token.getAccessToken();
   // 用户标识
   String openId = weixinOauth2Token.getOpenId();
   // 获取用户信息
   SNSUserInfo snsUserInfo = AdvancedUtil.getSNSUserInfo(accessToken, openId);[/align][align=left]   // 设置要传递的参数
   request.setAttribute("snsUserInfo", snsUserInfo);
  }
  // 跳转到index.jsp
  request.getRequestDispatcher("index.jsp").forward(request, response);
}
}[code=html]<servlet>
  <servlet-name>oauthServlet</servlet-name>
  <servlet-class>
   org.liufeng.course.servlet.OAuthServlet
  </servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>oauthServlet</servlet-name>
  <url-pattern>/oauthServlet</url-pattern>
</servlet-mapping>[/align][align=left] <welcome-file-list>
  <welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

[/code]