Filter实际应用案例

用户登录之后才能进入主页，用户注销之后就不能进入主页
1.用户登录之后，向session中放入用户的数据
2.进入主页时候要判断用户是否已经登录，在过滤器中实现

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        Object user_session = request.getSession().getAttribute("USER_SESSION");
        if (user_session==null) {
            response.sendRedirect("/show/error.jsp");
        }
        filterChain.doFilter(servletRequest,servletResponse) ;
    }