Content-Disposition 属性是作为对下载文件的一个标识字段，在rfc2616http://www.rfc-editor.org/rfc/rfc2616.pdf章节19.5 Additional Features中
有介绍，具体介绍请看http://www.rfc-editor.org/rfc/rfc1806.txt
字段介绍如下：
disposition :="Content-Disposition"":"
disposition-type
*(";"disposition-parm)
disposition-type:="inline"
/"attachment"
/ extension-token
; values are notcase-sensitive
disposition-parm := filename-parm / parameter
filename-parm :="filename""="value;
Content-Disposition属性有两种类型：inline 和 attachment
inline ：将文件内容直接显示在页面
Filefile=newFile("rfc1806.txt");
Stringfilename=file.getName();
response.setHeader("Content-Type","text/plain");
response.addHeader("Content-Disposition","inline;filename="+newString(filename.getBytes(),"utf-8"));
response.addHeader("Content-Length",""+ file.length());
attachment：弹出对话框让用户下载
Filefile=newFile("rfc1806.txt");
Stringfilename=file.getName();
response.setHeader("Content-Type","text/plain");
response.addHeader("Content-Disposition","attachment;filename="+newString(filename.getBytes(),"utf-8"));
response.addHeader("Content-Length",""+ file.length());
