Content-length
返回数据的大小，单位 bytes
Content-Type
常用
- application/octet-stream
- application/json
- application/javascript
- application/xml
- application/x-www-form-urlencoded
- text/plain
- text/xml
- text/html
- image/jpeg
- image/jpeg
- multipart/form-data
详细内容:http://tool.oschina.net/commons