Spring mvc interceptor配置拦截器，没有登录跳到登录页

<?xml  version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd" default-autowire="byName">
<!-- auto register Processor -->
<context:annotation-config />
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="com.anxin.msapweb.db.mybatis.mapper" />
</bean>

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="db2dataSource" />
</bean>

<mvc:interceptors>
<mvc:interceptor>
<!-- 需拦截的地址 -->
<!-- 一级目录 -->
<mvc:mapping path="/*.do" />
<mvc:mapping path="/*.ajax" />
<mvc:mapping path="/*.htm" />

<!-- 二级目录 -->
<mvc:mapping path="/*/*.do" />
<mvc:mapping path="/*/*.ajax" />
<mvc:mapping path="/*/*.htm" />
<!-- 需排除拦截的地址 -->
<mvc:exclude-mapping path="/login.htm"/>
<bean class="com.anxin.msapweb.web.interceptor.SecurityInterceptor" />
</mvc:interceptor>
</mvc:interceptors>
</beans>

package com.anxin.msapweb.web.interceptor;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import com.anxin.msapweb.common.Config;

public class SecurityInterceptor implements HandlerInterceptor {

private static final String LOGIN_URL = "/login.htm";

@Override
public boolean preHandle(HttpServletRequest req, HttpServletResponse res, Object handler) throws Exception {
HttpSession session = req.getSession(true);
// 从session 里面获取用户名的信息
Object obj = session.getAttribute(Config.Passport.SESSION_NAME_LOGIN_RESULT);
// 判断如果没有取到用户信息，就跳转到登陆页面，提示用户进行登陆
if (obj == null || "".equals(obj.toString())) {
res.sendRedirect(LOGIN_URL);
}
return true;
}

@Override
public void postHandle(HttpServletRequest req, HttpServletResponse res, Object arg2, ModelAndView arg3) throws Exception {
}

@Override
public void afterCompletion(HttpServletRequest req, HttpServletResponse res, Object arg2, Exception arg3) throws Exception {
}

}