[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index] [Thread Index] [Home]

GNUJSP caching page submission

Hi all,

Rob Chou just send me an interesting patch for adding caching to GNUJSP.
I have not yet made a proper patch for GNUJSP 0.9.10 but you can find
his complete source on the patches page
<http://www.klomp.org/gnujsp/patches.html>
Attached is the readme.
Thanks Rob.

Have fun,

Mark


Caching for GNUJSP 0.9.10 jsp pages
Robert Chou v1
===================================


Why?
----

I implement a lot of jsp pages simply to take
advantage of substitions for things like email
addresses, version numbers, etc.  I change these
values infrequently, but when I do, they get
propagated through my entire site.

This works great, but performance is slow.  It doesn't
return a content length and can't use keep alives.  It
also can't use the last modified dates for conditional
gets and heads.

So, for those pages which do not let users query
database tables for results, I added the ability for
GNUJSP to cache jsp's output.  I called this the
"cache_simple_html" directive.


How to use it
-------------

From here on, when I refer to GNUJSP, I refer to my
modified version.

By default, the new caching functionality is turned
off for ALL jsp pages.  To enable this new behavior,
you must first set the following servlet property:

cache_simple_html=true

For example, my zone.properties has this line:

servlet.gnujsp.initArgs=repository=c:\apps\jserv\gnujsp\generatedClassfiles,cache_simple_html=true

Next, you need to add a directive to every jsp file
which you want to cache.  For example, if you wanted
to cache /htdocs/main.jsp (which simply had substitutions
for your most current email address), add the following
line at the beginning of the file:

<%@ cache_simple_html="true" %>

<HTML>
...
...<%= bSomeBean.show_email_somehow() %>...
...

</HTML>

Now, bring up this page in your browser and the
page will show, after jsp compilation, as usual.
However, hit it again with telnet and you'll see
that it's now returning a last modified date, along
with a content length! (see Issues at end of readme
for info about apache/jserv bug).

If you take a look at your /htdocs directory, you
should now see a main.jsp.*.html along with your
main.html file.  (see How it works section below
for eplanation of the "*").

If you want to refresh this file, you can either
edit main.jsp, or delete this cache file.


Advanced options:
-----------------

Ok, so you've got most of you jsp's cached now,
and you change your email address.  What now?

1. You can either touch all the jsp files,

2. or you can use a script to delete all the
cache files (see how it works section on how to
uniquely identify cache html files).

3. set a "cache_recycle_millis" directive!

The following directive in a jsp file will recycle
the cache every 10 seconds:
<%@ cache_recycle_millis="10000" %>

The following directive in a jsp file will also recycle
the cache every 10 seconds:
<%@ cache_recycle_millis="s10" %>

The following directive in a jsp file will recycle
the cache every 10 minutes:
<%@ cache_recycle_millis="m10" %>

The valid prefixes are:
s=seconds
m=minutes
h=hours
d=days
w=weeks (7 days)


How it works
------------

Caching only works with GET and HEAD requests.
The caching directives will be ignored for PUT,
POST, etc.  You can even GET/POST to the same jsp
with cache enabled, with no ill effects.

QueryStrings for GETs are supported, but you should
only cache jsp pages where are not allowing the user
to selectively query from a database table.  Otherwise,
the cache files may get numerous.

Different character encodings are supported also.

Basically, here's a sample mapping from jsp file
to cache file names.

GET /main.jsp?test=abc HTTP/1.0

If caching is enabled, and main.jsp has the caching
directive, and main.jsp resides /htdocs.
The cache file will also reside in /htdocs, under the name:

main.jsp.test%3Dabc.ISO-8859-1.html

The querystring and character encoding is embedded
inside the cache file name.  You should be able to
uniquely identify jsp cache files with the mask
"*.jsp.*.html".


Issues:
-------

Q> If you return the last modfied date, then why does
a conditional get not return a 304 on cache files that
have not changed?  

A> This seems to be a bug somewhere in Apache/JServ.
I've contacted the apache mailing list for help.  The
header "If-Modified-Since" is always null to servlets
in Apache 1.3.6./JServ 1.0b5.