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From Dennis Dai <ddai...@ddai.net>
Subject Re: How do you set cache-control for static (gif, jpg) resources
Date Fri, 30 Jul 2004 20:07:17 GMT
I've been reading this thread back and forth for quite a few times :)

My observations are tomcat does send response code 304 on static 
contents (.js, .jpg, .gif, etc.), so I don't know why you said "Tomcat 
always returns Cache-Control: no-cache with every response" at the very 
beginning of this thread. Well I haven't done any request dump to see if 
that's the case, but I do see lots of 304s in my access log (which, I 
assume, is not quite possible if it sets Cache-Control to no-cache with 
every response).

Speaking of cache, there was an onJava article about caching with 
filter, but that's mostly for caching dynamically generated pages, which 
may or may not be of interests to you guys:

http://www.onjava.com/pub/a/onjava/2003/11/19/filters.html?page=3


Regards,

Dennis

On 7/30/2004 8:25 AM, Keith Bottner wrote:
> It must be something particular about Tomcat, or some other weirdness with
> my configuration. I will continue to look for the long term problem/solution
> when I have more time.
> 
> Thanks again,
> 
> Keith
> 
> -----Original Message-----
> From: Shapira, Yoav [mailto:Yoav.Shapira@mpi.com] 
> Sent: Friday, July 30, 2004 10:14 AM
> To: Tomcat Users List
> Subject: RE: How do you set cache-control for static (gif, jpg) resources
> 
> 
> 
> Hi,
> No problem about the help ;)  Sadly enough, I know most of the Servlet Spec
> by heart now. But more importantly, I have filters that do stuff on the
> request side, check the response headers, and then add headers on the
> response side, and they work just as the Spec says on every stable Tomcat
> version I've used within the last couple of years.
> 
> Yoav Shapira
> Millennium Research Informatics
> 
> 
>>-----Original Message-----
>>From: Keith Bottner [mailto:kbottner@comcast.net]
>>Sent: Friday, July 30, 2004 11:10 AM
>>To: 'Tomcat Users List'
>>Subject: RE: How do you set cache-control for static (gif, jpg)
> resources
>>
>>Actually I never got any IllegalStateExceptions. When I get some more
> time
>>I
>>will have to step through the Tomcat code and find out why I get called 
>>twice since I should only be getting called once.
>>
>>BTW, the 2.4 Servlet spec supports your analysis. It says the steps are 
>>(specifically step4-5):
>>
>>
>>Step 1: The method examines the request's headers.
>>
>>Step 2: The method may wrap the request object with a customized 
>>implementation of ServletRequest or HttpServletRequest in order to 
>>modify request headers or data.
>>
>>Step 3: The method may wrap the response object passed in to its
> doFilter
>>method with a customized implementation of ServletResponse or 
>>HttpServletResponse to modify response headers or data.
>>
>>Step 4: The filter may invoke the next entity in the filter chain. The
> next
>>entity may be another filter, or if the filter making the invocation is
> the
>>last
>>filter configured in the deployment descriptor for this chain, the next 
>>entity is the target Web resource. The invocation of the next entity is
> effected
>>by
>>calling the doFilter method on the FilterChain object, and passing in
> the
>>request and response with which it was called or passing in wrapped 
>>versions it may have created.
>>
>>The filter chain's implementation of the doFilter method, provided by
> the
>>container, must locate the next entity in the filter chain and invoke
> its
>>doFilter method, passing in the appropriate request and response
> objects.
>>Alternatively, the filter chain can block the request by not making the 
>>call to
>>invoke the next entity, leaving the filter responsible for filling out
> the
>>response
>>object.
>>
>>Step 5: After invocation of the next filter in the chain, the filter
> may
>>examine response headers.
>>
>>Step 6: Alternatively, the filter may have thrown an exception to
> indicate
>>an error in processing. If the filter throws an UnavailableException
> during
>>its doFilter processing, the container must not attempt continued 
>>processing down the filter chain. It may choose to retry the whole
> chain at
>>a later time if the exception is not marked permanent.
>>
>>Step 7: When the last filter in the chain has been invoked, the next
> entity
>>accessed is the target servlet or resource at the end of the chain.
>>
>>Step 8: Before a filter instance can be removed from service by the 
>>container, the container must first call the destroy method on the
> filter
>>to
>>enable the filter to release any resources and perform other cleanup 
>>operations.
>>
>>
>>Thanks for all you help, I appreciate your time.
>>
>>Keith
>>-----Original Message-----
>>From: Shapira, Yoav [mailto:Yoav.Shapira@mpi.com]
>>Sent: Friday, July 30, 2004 9:55 AM
>>To: Tomcat Users List
>>Subject: RE: How do you set cache-control for static (gif, jpg)
> resources
>>
>>
>>
>>Hi,
>>Yeah, I saw his response, but you didn't mention IllegalStateExceptions
> in
>>your log so I assumed the response being committed wasn't the problem
>>;)  Weird.
>>
>>Yoav Shapira
>>Millennium Research Informatics
>>
>>
>>>-----Original Message-----
>>>From: Keith Bottner [mailto:kbottner@comcast.net]
>>>Sent: Friday, July 30, 2004 10:45 AM
>>>To: 'Tomcat Users List'
>>>Subject: RE: How do you set cache-control for static (gif, jpg)
>>resources
>>>
>>>RequestDumperValve dump's the request and the response.
>>>
>>>So the request is first and the response follows the double dash line
>>for
>>>that request.
>>>
>>>Tim Funk though pointed out the problem.
>>>
>>>"You probably can't set headers after doChain() because the response
>>was
>>>committed."
>>>
>>>See his entire message for more details. For now my filter works, I
>>will
>>>just have to use setHeader instead of addHeader and be happy with it
>>being
>>>called twice.
>>>
>>>Keith
>>>
>>>-----Original Message-----
>>>From: Shapira, Yoav [mailto:Yoav.Shapira@mpi.com]
>>>Sent: Friday, July 30, 2004 9:28 AM
>>>To: Tomcat Users List
>>>Subject: RE: How do you set cache-control for static (gif, jpg)
>>resources
>>>
>>>
>>>
>>>Hola,
>>>How's the RequestDumperValve useful, if what you want to inspect are
>>the
>>>response headers?  Unless you're sending the response to another
> Tomcat
>>>server and this is the RequestDumperValve's log from that second
>>server?
>>>
>>>Yoav Shapira
>>>Millennium Research Informatics
>>>
>>>
>>>>-----Original Message-----
>>>>From: Keith Bottner [mailto:kbottner@comcast.net]
>>>>Sent: Friday, July 30, 2004 9:59 AM
>>>>To: 'Tomcat Users List'
>>>>Subject: RE: How do you set cache-control for static (gif, jpg)
>>>resources
>>>>
>>>>
>>>>
>>>>Unfortunately HttpServletResponse has now way to query the headers
>>only
>>>to
>>>>set them and determine if they exist. However I have the
>>>RequestDumperValve
>>>>for both editions of the code. Here is the log for the 1st set of
> code
>>>>(your suggestions).
>>>>
>>>>
>>>>: ---------------------------------------------------------------
>>>>:           authType=BASIC
>>>>:      contentLength=659
>>>>:        contentType=image/gif
>>>>:             header=Pragma=No-cache
>>>>:             header=Cache-Control=no-cache
>>>>:             header=Expires=Wed, 31 Dec 1969 18:00:00 CST
>>>>:             header=ETag=W/"659-1091194009140"
>>>>:             header=Last-Modified=Fri, 30 Jul 2004 13:26:49 GMT
>>>>:            message=null
>>>>:         remoteUser=username
>>>>:             status=200
>>>>:             scheme=http
>>>>:         serverName=localhost
>>>>:         serverPort=8080
>>>>:        servletPath=/common/inject/emp-ui-bg-con-tl.gif
>>>>:           isSecure=false
>>>>: ---------------------------------------------------------------
>>>>: ---------------------------------------------------------------
>>>>:           authType=BASIC
>>>>:      contentLength=7675
>>>>:        contentType=image/gif
>>>>:             header=Pragma=No-cache
>>>>:             header=Cache-Control=no-cache
>>>>:             header=Expires=Wed, 31 Dec 1969 18:00:00 CST
>>>>:             header=ETag=W/"7675-1091194009140"
>>>>:             header=Last-Modified=Fri, 30 Jul 2004 13:26:49 GMT
>>>>:            message=null
>>>>:         remoteUser=username
>>>>:             status=200
>>>>
>>>>Above you can see that none of my changes to the response stream were
>>>used.
>>>>
>>>>
>>>>Here is the headers for the 2nd set of code (the original)
>>>>
>>>>: ---------------------------------------------------------------
>>>>: REQUEST URI       =/common/inject/emp-ui-bg-con-tl.gif
>>>>:           authType=BASIC
>>>>:  characterEncoding=null
>>>>:      contentLength=-1
>>>>:        contentType=null
>>>>:        contextPath=
>>>>:             cookie=JSESSIONIDSSO=47372C3C7BB03505C936A20970ACB1F9
>>>>:             cookie=JSESSIONID=B75E4FA2AA8047CCD40A885A0A84DFB5
>>>>:             header=accept=*/*
>>>>:             header=accept-language=en-us
>>>>:             header=accept-encoding=gzip, deflate
>>>>:             header=user-agent=Mozilla/4.0 (compatible; MSIE 6.0;
>>>Windows
>>>>NT 5.1; .NET CLR 1.0.3705; .NET CLR 1.1.4322)
>>>>:             header=host=localhost:8080
>>>>:             header=connection=Keep-Alive
>>>>:             header=authorization=Basic ZGhhbHBpbjpkaGFscGlu
>>>>:             locale=en_US
>>>>:             method=GET
>>>>:           pathInfo=null
>>>>:           protocol=HTTP/1.1
>>>>:        queryString=null
>>>>:         remoteAddr=127.0.0.1
>>>>:         remoteHost=127.0.0.1
>>>>:         remoteUser=username
>>>>: requestedSessionId=B75E4FA2AA8047CCD40A885A0A84DFB5
>>>>:             scheme=http
>>>>:         serverName=localhost
>>>>:         serverPort=8080
>>>>:        servletPath=/common/inject/emp-ui-bg-con-tl.gif
>>>>:           isSecure=false
>>>>: ---------------------------------------------------------------
>>>>: ---------------------------------------------------------------
>>>>:           authType=BASIC
>>>>:      contentLength=7675
>>>>:        contentType=image/gif
>>>>:             header=Pragma=No-cache
>>>>:             header=Cache-Control=no-cache
>>>>:             header=Cache-Control=max-age=1800
>>>>:             header=Expires=Wed, 31 Dec 1969 18:00:00 CST
>>>>:             header=Cache-Control=no-cache
>>>>:             header=Cache-Control=max-age=1800
>>>>:             header=ETag=W/"7675-1091159753343"
>>>>:             header=Last-Modified=Fri, 30 Jul 2004 03:55:53 GMT
>>>>:            message=null
>>>>:         remoteUser=username
>>>>:             status=200
>>>>
>>>>
>>>>Do you see the duplicate Cache-Control above? The first 
>>>>Cache-control=no-cache is the default then my addition then another
>>>filter
>>>>adds the Expires and then both of the cache control lines are added
>>>again.
>>>>
>>>>Thanks for the performance tip, now if I can just get this!
>>>>
>>>>I appreciate any help you can offer.
>>>>
>>>>Keith
>>>>
>>>>-----Original Message-----
>>>>
>>>>From: Shapira, Yoav [mailto:Yoav.Shapira@mpi.com]
>>>>Sent: Friday, July 30, 2004 8:40 AM
>>>>To: Tomcat Users List
>>>>Subject: RE: How do you set cache-control for static (gif, jpg)
>>>resources
>>>>
>>>>
>>>>
>>>>Hi,
>>>>
>>>>>Previously I was calling doChain at the end of my doFilter method.
>>>>>
>>>>>Making the change you suggest, calling doChain at the top like
>>>><snip />
>>>>>DOES NOT INSERT any of my changes into the response stream. If I do
>>it
>>>>like
>>>>>this:
>>>><snip />
>>>>>Then I get two additions in the response stream.
>>>>>
>>>>>Any more ideas?
>>>>
>>>>That's a bit strange.  Are you wrapping the response or setting these 
>>>>headers elsewhere?  Can you print out to the log a listing of all the 
>>>>response headers at the end of your filter?
>>>>
>>>>The addHeader method allows for multiple values, but many readers
> will
>>>only
>>>>see the first.  So if something in your code sets the cache-control
>>>header,
>>>>then you call it again, the header will be present twice with two
>>>values
>>>>(which is legal in the HTTP protocol for most headers).
>>>>
>>>>As an aside, you can read the enumeration of the init parameters in
>>the
>>>>filter's init method, store it in some member variable, and that will 
>>>>improve the performance of your filter because you won't have to do
> it
>>>on
>>>>every request.
>>>>
>>>>Yoav Shapira
>>>>
>>>>

-- 
Dennis Dai
ddai@ddai.net

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