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A.7 Generating the Server Response: HTTP Response Headers

529

browser supports a given encoding (by checking the 

Accept Encoding

request header) before using it. See compression example in 

Section 4.4.

  Content Length: the number of bytes in the response. See 

setContentLength

 above.

  Content Type: the MIME type of the document being returned. See 

setContentType

 above.

  Expires: the time at which document should be considered out of date 

and thus should no longer be cached. Use 

setDateHeader

 to set this 

header.

  Last Modified: the time document was last changed. Don't set this 

header explicitly; provide a 

getLastModified

 method instead. See 

example in Section 2.8.

  Location: the URL to which browser should reconnect. Use 

sendRedirect

 instead of setting this header directly. For an example, 

see Section 6.3.

  Pragma: a value of 

no cache

 instructs HTTP 1.0 clients not to cache 

document. See the 

Cache Control

 response header (Section 7.2).

  Refresh: the number of seconds until browser should reload page. Can 

also include URL to connect to. For an example, see Section 7.3.

  Set Cookie: the cookies that browser should remember. Don't set this 

header directly; use 

addCookie

 instead. See Chapter 8 for details.

  WWW Authenticate: the authorization type and realm client should 

supply in its 

Authorization

 header in the next request. For an 

example, see Section 4.5.

Generating GIF Images from Servlets

  Create an Image.

Use the 

createImage

 method of 

Component

.

  Draw into the Image.

Call 

getGraphics

 on the 

Image

, then do normal drawing operations.

  Set the Content Type response header.

Use 

response.setContentType("image/gif")

.

  Get an output stream.

Use 

response.getOutputStream()

.

  Send the Image down output stream in GIF format.

Use Jef Poskanzer's 

GifEncoder

. See http://www.acme.com/java/.

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.