private FilterConfig config = null;    @Override    public void init(FilterConfig config) throws ServletException {        this.config = config;    }    @Override    public void destroy() {        this.config = null;    }    /**     *      * @author wwhhf     * @since 2016/5/30     * @comment 跨域的设置     */    @Override    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException {        HttpServletResponse httpResponse = (HttpServletResponse) response;        // 表明它允许"http://xxx"发起跨域请求        httpResponse.setHeader("Access-Control-Allow-Origin",                config.getInitParameter("AccessControlAllowOrigin"));        // 表明在xxx秒内，不需要再发送预检验请求，可以缓存该结果        httpResponse.setHeader("Access-Control-Allow-Methods",                config.getInitParameter("AccessControlAllowMethods"));        // 表明它允许xxx的外域请求        httpResponse.setHeader("Access-Control-Max-Age",                config.getInitParameter("AccessControlMaxAge"));        // 表明它允许跨域请求包含xxx头        httpResponse.setHeader("Access-Control-Allow-Headers",                config.getInitParameter("AccessControlAllowHeaders"));        chain.doFilter(request, response);    }