网上图书商城10--前台登录过滤器

<filter>
	<filter-name>LoginFilter</filter-name>
	<filter-class>cn.itcast.goods.web.filter.LoginFilter</filter-class>
</filter>
<filter-mapping>
	<filter-name>LoginFilter</filter-name>
	<url-pattern>/jsps/cart/*</url-pattern>
</filter-mapping>
<filter-mapping>
	<filter-name>LoginFilter</filter-name>
	<servlet-name>CartItemServlet</servlet-name>
</filter-mapping>
<filter-mapping>
	<filter-name>LoginFilter</filter-name>
	<url-pattern>/jsps/order/*</url-pattern>
</filter-mapping>
<filter-mapping>
	<filter-name>LoginFilter</filter-name>
	<servlet-name>OrderServlet</servlet-name>
</filter-mapping>

public void doFilter(ServletRequest request, ServletResponse response,
		FilterChain chain) throws IOException, ServletException {
	/*
	 * 1. 获取session中的user
	 * 2. 判断是否为null
	 *   > 如果为null：保存错误信息，转发到msg.jsp
	 *   > 如果不为null：放行
	 */
	HttpServletRequest req = (HttpServletRequest) request;
	Object user = req.getSession().getAttribute("sessionUser");
	if(user == null) {
		req.setAttribute("code", "error");//为了显示X图片
		req.setAttribute("msg", "您还没有登录，不能访问本资源");
		req.getRequestDispatcher("/jsps/msg.jsp").forward(req, response);
	} else {
		chain.doFilter(request, response);//放行
	}
}