这个其实是在web.xml文件中配置mime下载文件类型就可以了，配置的示例：
<mime-mapping>
<extension>doc</extension>
<mime-type>application/msword</mime-type>
</mime-mapping>
<mime-mapping>
<extension>xls</extension>
<mime-type>application/msexcel</mime-type>
</mime-mapping>
<mime-mapping>
<extension>pdf</extension>
<mime-type>application/pdf</mime-type>
</mime-mapping>
<mime-mapping>
<extension>zip</extension>
<mime-type>application/zip</mime-type>
</mime-mapping>
<mime-mapping>
<extension>rar</extension>
<mime-type>application/rar</mime-type>
</mime-mapping>
<mime-mapping>
<extension>txt</extension>
<mime-type>application/txt</mime-type>
</mime-mapping>
<mime-mapping>
<extension>chm</extension>
<mime-type>application/mshelp</mime-type>
</mime-mapping>
这样就可以防止在浏览器是直接打开文件，而是弹出下载框供用户下载了。
