Hi,
right this is a know problem and discussed several times, we should
start solving this. :-)
I suggest that we make the Plugin Class implementing the Configurable
interface. In case a plugin needs any configuration value it will
request them from the plugin instance.
The next step would be changing the plugin Registry from a singleton
to a normal object that need to be instantiated with a nutch
configuration object in the constructor.
In general I suggest we use a Inversion of control style mechanism
(http://www.martinfowler.com/articles/injection.html) to solve these
kind of problems, this is from my point of view the cleanest possible
solution and allows also changing e.g. configuration objects until
runtime.
Stefan
Am 20.12.2005 um 14:19 schrieb Andrzej Bialecki:
Hi,
This was mentioned before: there are many places in Nutch that rely
on static initializers. This is so-so or sometimes plainly bad,
depending on a situation.
I'm facing a problem now with URLFilters. I need to run several
fetchers inside a single VM, with different parameters such as
different url patterns (which is handled by URLFilters). But even
if I specify different NutchConf-s to each fetcher, the list of
implementations and the instances of URLFilter[] in URLFilters are
initialized only once, and this happens from the default
configuration obtained through a call to static NutchConf.get().
I would like to change it somehow, but I'm not sure how... One way
to solve this would be to instantiate the plugins based on a
concrete NutchConf instance, like this:
URLFilters:
private URLFilters(NutchConf) {
// initialize plugins based on this instance of NutchConf
}
public static URLFilters get(NutchConf conf) {
URLFilters res = (URLFilters)conf.get("urlfilters.key");
if (res == null) {
res = new URLFilters(conf);
conf.put("urlfilters.key", res);
}
return res;
}
In case you are running with a single NutchConf per JVM it doesn't
change anything. In case you want to run several different configs
in a single JVM this approach provides the solution. We could
follow this strategy for other plugin registry facades. Comments?
--
Best regards,
Andrzej Bialecki <><
___. ___ ___ ___ _ _ __________________________________
[__ || __|__/|__||\/| Information Retrieval, Semantic Web
___|||__|| \| || | Embedded Unix, System Integration
http://www.sigram.com Contact: info at sigram dot com
