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148

Chapter 7 Generating the Server Response: HTTP Response Headers

details (you can access RFCs on line at one of the archive sites listed at 

http://www.rfc editor.org/

).

Content Length

This header indicates the number of bytes in the response. This infor 

mation is needed only if the browser is using a persistent (keep alive) 

HTTP connection. See the 

Connection

 header for determining when 

the browser supports persistent connections. If you want your servlet to 

take advantage of persistent connections when the browser supports it, 

your servlet should write the document into a 

ByteArrayOutput 

Stream

, look up its size when done, put that into the 

Content Length

field with 

response.setContentLength

, then send the content via 

byteArrayStream.writeTo(response.getOutputStream())

. For 

an example of this approach, see Section 7.4.

Content Location

This header supplies an alternative address for the requested docu 

ment. 

Content Location

 is informational; responses that include this 

header also include the requested document, unlike the case with the 

Location

 header. This header is new to HTTP 1.1.

Content MD5

The 

Content MD5

 response header provides an MD5 digest for the 

subsequent document. This digest provides a message integrity check 

for clients that want to confirm they received the complete, unaltered 

document. See RFC 1864 for details on MD5. This header is new in 

HTTP 1.1.

Content Range

This new HTTP 1.1 header is sent with partial document responses and 

specifies how much of the total document was sent. For example, a value 

of  

bytes 500 999/2345

  means that the current response includes 

bytes 500 through 999 of a document that contains 2345 bytes in total.

Content Type

The 

Content Type

 header gives the MIME (Multipurpose Internet 

Mail Extension) type of the response document. Setting this header is 

so common that there is a special method in 

HttpServletResponse

 for 

it: 

setContentType

. MIME types are of the form 

maintype/subtype

for officially registered types, and of the form 

maintype/x subtype

 for 

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