goja-web/src/main/java/goja/mvc/kits/Servlets.java
public static boolean checkIfModifiedSince(HttpServletRequest request,
                                               HttpServletResponse response,
                                               long lastModified) {
        long ifModifiedSince = request.getDateHeader(HttpHeaders.IF_MODIFIED_SINCE);
        if ((ifModifiedSince != -1) && (lastModified < (ifModifiedSince + 1000))) {
            response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            return false;
        }
        return true;
    }
public static boolean checkIfModifiedSince(HttpServletRequest request,
                                               HttpServletResponse response,
                                               long lastModified) {
        long ifModifiedSince = request.getDateHeader(HttpHeaders.IF_MODIFIED_SINCE);
        if ((ifModifiedSince != -1) && (lastModified < (ifModifiedSince + 1000))) {
            response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            return false;
        }
        return true;
    }
根据浏览器If-Modified-Since Header, 计算文件是否已被修改. <p/> 如果无修改, checkIfModify返回false ,设置304 not modify
status.

@param lastModified 内容的最后修改时间.