24-filter-拦截器

在web.xml里面配置，有两种形式：

然后编写filter类：

	@Override
	public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
			throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest)arg0;
		HttpServletResponse response = (HttpServletResponse)arg1;
		HttpSession session = request.getSession();
		if(session.getAttribute("admin") == null && request.getRequestURL().indexOf("/admin/login") == -1) {
			response.sendRedirect(request.getContextPath()+"/admin/login");
		}else {
			arg2.doFilter(arg0, arg1);
		}
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		//@Description: TODO
	}