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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters

Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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You must implement destroy()
but usually itÕs empty.
Every Þ lter MUST implement
the Filter interface.
You must implement init(), usually you
just save the conÞ g object.
doFilter() is where you do the real
work Notice that the method doesnÕt
take HTTP request and response
objects just regular ServletRequest and
ServletResponse objects.
But weÕre pretty sure
that we can cast the
request and response to
their HTTP subtypes.
This is how the next Þ lter or servlet
in line gets called - lots more on this
in the next couple of pages.
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Filter and FilterChain
are in javax.servlet
Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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ALREADYMENTIONEDTHATTHEFILTERSNOTTOMENTION
THESERVLETSHOULDNTKNOWANYTHINGABOUTTHE

OTHERFILTERSINVOLVEDINTHEREQUESTBUTSOMEONE
NEEDSTOKNOWTHEORDERANDTHATSOMEONEISTHE
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.

This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:

Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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The ÒMyResponseÓ object
delegates (passes-through),
most of the calls it receives,
to the ÒrealÓ response object.
The ÒMyResponseÓ object also has a custom
output stream that compresses the data
written by the servlet, and then sends the
compressed data to the original output
stream (that goes back to the client).
The Þ lter passes a custom ÒMyResponseÓ,
which implements HttpServletResponse
(instead of the original REAL response
the Container passed to the Þ lter).
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THENON(440INTERFACE3ERVLET2ESPONSEBUTTODAYTHECHANCESOFSOMEONE
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:

O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Remember, to implement
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both it and its superinterface
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters

Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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now letÕs assume Gzip
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extends
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ServletOutputStream to
whoever asks for one.
Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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put will be compressed.
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gives the compression Þ lter a handle on the
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:

Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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servlet output stream.
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stream, only if the servlet has not already
accessed the print writer.
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stream with our compression
servlet output stream.
To make a print writer, we have
to Þ rst wrap the servlet output
stream and then wrap the
compression servlet output stream
in two additional output stream
decorators: OutputStreamWriter
which converts characters into
bytes, and then a PrintWriter on
top of the OutputStreamWriter

object.
Provide access to a decorated
print writer.
Allow the servlet to access a print writer,
only if the servlet has not already accessed
the servlet output stream.
Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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wrapping the TCP network output stream to the client).
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instance variable is package-private to allow the
compression response wrapper access to this variable
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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PRFNH[DP
Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.

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
PRFNH[DP
Chapter 13. The Power of Filters
Chapter 13. The Power of Filters
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:
O'Reilly
Prepared for Augusto Jaramillo Forcada, Safari ID:
Print Publication Date: 8/1/2004 User number: 729515 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.