Hi Stuart and Monika, I've been working with this issue and this
approach worked well with my DSpace instance:
- the date that DSpace stores as last modified has a big precision, and
the date that we receive from the http header "Last-Modified" doesn't
have precision enough (only with seconds), so when DSpace receives the
LastModified date from the item in milliseconds is different from the
date that gets from the http header in milliseconds.
- to avoid this issue I've created two Date classes and compare this
objects with the methods "before" or "after" and worked well:
if (isSpider)
{
// Check for if-modified-since header -- ONLY if not
authenticated
long modSince = request.getDateHeader("If-Modified-Since");
java.util.Date d1= new java.util.Date(modSince);
// if (modSince != -1 && item != null &&
item.getLastModified().getTime() <= modSince)
if (modSince != -1 && item != null &&
(item.getLastModified().toGMTString().equals(d1.toGMTString())||item.getLastModified().before(d1))
)
{
// Item has not been modified since requested date,
// hence bitstream has not; return 304
response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
return;
}
}
If you have a look at the code you'll see that this only works if DSpace
detects that this is a spider. To do this I tried with a curl request
like this:
curl -v -A "Mozilla/5.0 (compatible; Googlebot/2.1;
+http://www.google.com/bot.html)2011-05-19 10:53:08" -z 'Wed, 13 Apr
2011 00:32:26 GMT' 'http://.....sequence=1'
and it worked well.
I hope that this helps.
Best regards,
Jesús
On 05/09/2011 10:52 PM, Stuart Lewis wrote:
> Hi Monika,
>
>> There appears to be a problem with last modified handling of bitstreams
>>
>> For the bitstream
>> http://scholars.indstate.edu/bitstream/10484/108/1/Yazvac.pdf
>> the last modified is reported as Thu, 06 Jan 2011 17:54:26
>>
>> but requesting the stream with
>> curl -z 'Thu, 06 Jan 2011 17:54:26 GMT'
>> http://scholars.indstate.edu/bitstream/10484/108/1/Yazvac.pdf
>> returns the bitstream itself
>>
>> curl realizes that the bitstream is unchanged when doing (date + 1second)
>> curl -z 'Thu, 06 Jan 2011 17:54:27 GMT'
>> http://scholars.indstate.edu/bitstream/10484/108/1/Yazvac.pdf
>>
>> I found the same behavior for a bitstream from another DSPACE instance:
>> http://smartech.gatech.edu/bitstream/handle/1853/32992/museum_program.pdf?sequence=3
>>
>> It seems that the servlet may compare last modified dates with>= instead of>
>> Where can I check/fix this ?
> Take a look in:
>
> -
> dspace-jspui/dspace-jspui-api/src/main/java/org/dspace/app/webui/servlet/BitstreamServlet.java
>
> And look for the following code:
>
> // Check for if-modified-since header
> long modSince = request.getDateHeader("If-Modified-Since");
>
> if (modSince != -1&& item.getLastModified().getTime()<
> modSince)
> {
> // Item has not been modified since requested date,
> // hence bitstream has not; return 304
> response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
> return;
> }
>
> That might be the bit to check.
>
> Last modified date for an item is based on the last date that the item was
> modified (e.g. metadata updated, new file uploaded).
>
> Thanks,
>
>
> Stuart Lewis
> Digital Development Manager
> Te Tumu Herenga The University of Auckland Library
> Auckland Mail Centre, Private Bag 92019, Auckland 1142, New Zealand
> Ph: +64 (0)9 373 7599 x81928
>
>
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