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4.3 HTTP 1.1 Request Headers

101

Content Type

Although this header is usually used in responses from the server, it can 

also be part of client requests when the client attaches a document as 

the 

POST

 data or when making 

PUT

 requests. You can access this header 

with the shorthand 

getContentType

 method of 

HttpServletRequest

.

Cookie

This header is used to return cookies to servers that previously sent 

them to the browser. For details, see Chapter 8 (Handling Cookies). 

Technically, 

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.

Expect

This rarely used header lets the client tell the server what kinds of 

behaviors it expects. The one standard value for this header, 

100 con 

tinue

, is sent by a browser that will be sending an attached document 

and wants to know if the server will accept it. The server should send a 

status code of either 100 (

Continue

) or 417 (

Expectation Failed

) in 

such a case. For more details on HTTP status codes, see Chapter 6 

(Generating the Server Response: HTTP Status Codes).

From

This header gives the e mail address of the person responsible for the 

HTTP request. Browsers do not send this header, but Web spiders 

(robots) often set it as a courtesy to help identify the source of server 

overloading or repeated improper requests.

Host

Browsers are required to specify this header, which indicates the host 

and port as given in the original URL. Due to request forwarding and 

machines that have multiple hostnames, it is quite possible that the 

server could not otherwise determine this information. This header is 

not new in HTTP 1.1, but in HTTP 1.0 it was optional, not required.

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