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Chapter

response from a Web server normally consists of a status line, one or

more response headers, a blank line, and the document. To get the

A

most out of your servlets, you need to know how to use the status line

and response headers effectively, not just how to generate the document.

Setting the HTTP response headers often goes hand in hand with setting

the status codes in the status line, as discussed in the previous chapter. For

example, all the  document moved  status codes (300 through 307) have an

accompanying 

Location

 header, and a 401 (

Unauthorized

) code always

includes an accompanying 

WWW Authenticate

 header. However, specifying

headers can also play a useful role even when no unusual status code is set.

Response headers can be used to specify cookies, to supply the page modifi 

cation date (for client side caching), to instruct the browser to reload the

page after a designated interval, to give the file size so that persistent HTTP

connections can be used, to designate the type of document being generated,

and to perform many other tasks. 

7.1 Setting Response Headers 

from Servlets

The most general way to specify headers is to use the 

setHeader

 method of

HttpServletResponse

. This method takes two strings: the header name and

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