由于安全因素android webview屏蔽了文件上传控件，但是他并没有完全封掉。

<form method="POST" enctype="multipart/form-data">
File to upload: <input type="file" name="uploadfile">&nbsp;&nbsp;
<input type="submit" value="Press to Upload..."> to upload the file!
</form>

1.activity定义