大佬教的，做个笔记

//Spring管理类中获取requets.attributes
ServletRequestAttributes attrs = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
if (attrs == null) {
    // throw new IllegalStateException("当前线程中不存在 Request 上下文");
}else{
    //信息源
    Properties properties = System.getProperties();
    //获取真实项目路径（'.../webapps' + '/images/testLog.txt'）
    String logRealPath = attrs.getRequest().getServletContext().getRealPath("/images/testLog.txt");
    //开启流
    OutputStream out=new FileOutputStream(logRealPath,true);
    //拿到系统信息
    Set<Map.Entry<Object, Object>> entries = properties.entrySet();
    //打印到文件当中
    for (Map.Entry entry:entries
         ) {
        out.write(entry.getKey().toString().getBytes("UTF-8"));
        out.write("-->".getBytes("UTF-8"));
        out.write(entry.getValue().toString().getBytes("UTF-8"));
        out.write("\n".getBytes("UTF-8"));
    }

    //关闭流
    out.close();
}

//浏览器输入项目路径/images/testLog.txt查看
查找“file.encoding”