Hi Nathan,
John Caron wrote:
Nathan, I've answered a little bit, but I need to forward this to
ethan to answer most of these questions, I hope he's watching his
email to answer soon.
Nathan Potter wrote:
John,
So I made this catalog.xml:
<?xml version="1.0" encoding="UTF-8"?>
<catalog name="TestData_NC" version="1.0.1"
xmlns="http://www.unidata.ucar.edu/namespaces/thredds/
InvCatalog/v1.0">
<service name="TestData" serviceType="OpenDAP" base="/thredds/
contextPath/"/>
<datasetScan location="/nc" path="nc" name="Test netCDF Data"
serviceName="OpenDAP">
<crawlableDatasetImpl
className="opendap.olfs.S4CrawlableDataset">
</datasetScan>
</catalog>
And I have questions:
- In the <service> element what is the attribute "base" set to, the
location of the servlet:
$CATALINA_HOME/webapps/myservlet
Or is it set to:
$CATALINA_HOME/content/thredds
The service base is the (first part of the) external URL of the
dataset, that is the URL that your clients will see. Since this
determines which servlet gets called when it comes into Tomcat, you
need to make sure it matches. I prefer using
"/contextName/servletMapping/", which then makes it reletive to the
catalog URL. The contextName matches your war file, and the
servletMapping matches what you put into the web.xml. So if your war
file is opendap.war, and you have
<servlet-mapping>
<servlet-name>DefaultHandlerServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
in your web.xml,
then use /opendap/ as the service base, and the DefaultHandlerServlet
will bet called when any URLS of the form
http://servername:8080/opendap/
get sent.
- Given that I identify my implementation of CrawlableDataset to the
THREDDS code as above, how do I get one built? The constructor
requires both a path and a config object, and that config object is
something I have and THREDDS doesn't. Seems like I either need to
pass an instance of my CrawlableDataset, or my config object, into
CatalogRootHandler.
I think the code will instantiate an object for you.
ethan?
Your CrawlableDataset will be passed an org.jdom.Element object that is
the child of the crawlableDatasetImpl element. That is the only thing
that is supported at the moment.
- Logging: I read the basic docs on the Log4j and the Simple Logging
Facade. I like this. I don't understand how to use it. I am
concerned that my hacks to get THREDDS into my servlet don't address
a number of startup issues surrounding logging that THREDDS may
require. You're ThreddsDefault.makeDebugActions() is pretty
involved, and I don't really get it.
There's a question of how much of the thredds framework you want to
use. If you want to use all of it, thats great, we can leverage each
others work. The DebugActions allow remote testing and info. Very
useful. I can give you permssion to look at how the TDS on motherlode
works if you want. Anyway, you need to decide whether to use all or a
part of it.
The SLF/Log4j is worth useing in any case.
- Caching: It looks like caching is an integral part of your code
base. Is it isolated in the servlet related code, or are there
implementations of caching related activities in the catalog stuff
that I need to be aware of?
Im using caching deep in my data server, but not in the servlet
handling part. So you still have a choice.
I am NOT talking to a filesystem. I can't give THREDDS a file root,
or a file type/format. I can give provide a CrawlableDataset
instance that can traverse the data store. I can hand you all of
the traditional OPeNDAP/DODS responses, although from what I got
from Ethan's description once I get the catalog working I would have
my servlet to respond to a DODS request for, say a DDS, by calling
CatalogRootHandler.findRequestedDataset(...) for the data set, then
if a CRawlableDataset comes back (indicating that this data set
exists and is not filtered) I can use the CrawlableDataset to do
what I need to get the stuff to send to the client. Is that true?
We undersstand that, thats what CrawlableDataset does for you.
Ethan can you explain his next steps?
I think you've got it Nathan. You check that a CrawlableDataset is
allowed for that path by calling findRequestedDataset(...). If you get a
CrawlableDataset back, you can cast it to a
opendap.olfs.S4CrawlableDataset and call whatever access
information/methods you need to on that. We would cast to
CrawlableDatasetFile and call getFile() on it.
Ethan
Lets just incrementally get this working one step at a time. First
thing is to get catalogs generated using CrawlableDataset.
Dont worry, we will get all this working ASAP.
--
Ethan R. Davis Telephone: (303) 497-8155
Software Engineer Fax: (303) 497-8690
UCAR Unidata Program Center E-mail: edavis@xxxxxxxx
P.O. Box 3000
Boulder, CO 80307-3000 http://www.unidata.ucar.edu/
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