# 大文件上传

php中目前的上传原理:上传的整个文件提交到服务器的临时目录,然后再把临时目录的文件移动要需要的保存的地方,php]默认执行的时间是30s,如果一个文件超大,很可能会发生超时.(并且通常post的最大文件M数都是有限制的),导致上传不成功

## **大文件上传的方法:**

* 客户端控件: 需要本地安装指定控件
* 采用swfUpload、uploaddify等Flash组件
* 用XMLHttpRequest实现文件上传和断点续传

## XMLHttpRequest 2.0 的新特性

* 可以上传文件
* 可以设置HTTP请求的时限
* 可以使用FormData对象管理表单数据
* 可以请求不同域名下的数据（跨域请求）
* 可以获取服务器端的二进制数据
* 可以获得数据传输的进度信息


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