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7.2 HTTP 1.1 Response Headers and Their Meaning

153

Set Cookie

The 

Set Cookie

 header specifies a cookie associated with the page. 

Each cookie requires a separate 

Set Cookie

 header. Servlets should not 

use 

response.setHeader("Set Cookie", ...)

, but instead should 

use the special purpose 

addCookie

 method of 

HttpServletResponse

. 

For details, see Chapter 8 (Handling Cookies). Technically, 

Set Cookie

is not part of HTTP 1.1. It was originally a Netscape extension but is now 

very widely supported, including in both Netscape and Internet Explorer.

Trailer

This new and rarely used HTTP 1.1 header identifies the header fields 

that are present in the trailer of a message that is sent with  chunked  

transfer coding. See Section 3.6 of the HTTP 1.1 specification (RFC 

2616) for details. Recall that 

http://www.rfc editor.org/

 maintains 

an up to date list of RFC archive sites.

Transfer Encoding

Supplying this header with a value of 

chunked

 indicates  chunked  

transfer coding. See Section 3.6 of the HTTP 1.1 specification (RFC 

2616) for details.

Upgrade

This header is used when the client first uses the 

Upgrade

 request 

header to ask the server to switch to one of several possible new proto 

cols. If the server agrees, it sends a 101 (

Switching Protocols

) status 

code and includes an 

Upgrade

 response header with the specific proto 

col it is switching to. This protocol negotiation is usually carried on by 

the server itself, not by a servlet.

Vary

This rarely used new HTTP 1.1 header tells the client which headers 

can be used to determine if the response document can be cached.

Via

This header is used by gateways and proxies to list the intermediate sites 

the request passed through. It is new in HTTP 1.1.

Warning

This new and rarely used catchall header lets you warn clients about 

caching or content transformation errors.

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