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From "Osipov, Michael" <michael.osi...@siemens.com>
Subject RE: Availability of a resource in a realm
Date Thu, 19 Apr 2012 07:15:05 GMT
Konstantin Kolinko wrote:
> 2012/4/18 Osipov, Michael <michael.osipov@siemens.com>:
>> Konstantin Kolinko wrote:
>>> 2012/4/17 Osipov, Michael <michael.osipov@siemens.com>:
>>>> Hi folks,
>>>> 
>>>> I have a resource declared in my context.xml (not a resource link).
>>>> I want to retrieve that resource as soon as possible in my realm. I
>>>> tried start() and init() but it seems like that at this time the
>>>> InitialContext is not available. So at what time can I expect the
>>>> context being "complete"? 
>>>> 
>>>> I am on Tomcat 6.0.35
>>>> 
>>> 
>>> Look at DataSourceRealm for an example.
>>> 
>>> IIRC, what is seen as InitialContext depends on the value of
>>> Thread.getContextClassLoader() when InitialContext instance is
>>> created.
>> 
>> I have found the spot. Thanks!
>> You have the same approach as me. Prior authentication you retrieve
>> the resource. But, I do cache the resource object you don't. Are
>> there any implications? How costly is a recurring lookup?  
> 
> Personally, I'd cache the DataSource obtained through the lookup.  I
> think it is oversight, though maybe it makes the realm more manageable
> through JMX.

A doCache property would be nice though I do not use this realm.

> During first releases of Tomcat 7 there was some discussion about
> objects created by factories in JNDI. Tomcat approach was to cache the
> created object and return it for further lookups. Some recent JavaEE
> spec required a new instance of the object to be created on each
> lookup.   We updated implementation in early Tomcat 7 releases to
> match the recent spec, but had to revert on users' demands, making it
> configurable. See "singleton" attribute
> http://tomcat.apache.org/tomcat-7.0-doc/config/context.html
> 
> If each lookup created a new DataSource instance it would certainly be
> expensive.
> 
> I'd say that DataSourceRealm does not create new InitialContext
> instance, so that avoids some initialization overhead. I do not know
> how expensive is the lookup itself.

Thanks for the insight. I ended up init my object like this:

protected synchronized void initDirContextSource()
			throws NamingException {
		
		if (dirContextSource == null) {
			Context context = null;
			if (localDirContextSource) {
				context = ContextBindings.getClassLoader();
	            context = (Context) context.lookup("comp/env");
			} else {
				StandardServer server = (StandardServer) ServerFactory.getServer();
                context = server.getGlobalNamingContext();
			}
			
			dirContextSource = (DirContextSource) context.lookup(dirContextSourceName);
		}
	}

Which is called by getPrincipal.


Michael

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