On Wednesday 24 December 2003 07:33, Marco Tedone wrote:
> ----- Original Message -----
> From: "Niclas Hedhman" <[EMAIL PROTECTED]>
> > Furthermore, I think that "ohh, the service I need is now available,
> > let's use it." is intrinsic to the LifeCycle of all (but the most simple)
> > components.
>
> Could you make an example?
Almost all systems are based on some form of lookup of service, whether it be
Avalon ServiceManager, JNDI, JDBC connects, whatever.
So the code would be;
SomeService s = (SomeService) provider.lookup( whatever );
s.useService();
which makes a lot of assumptions about what is available. This is the most
important lesson from learning Jini.
In truly distributed and robust environments, a client doesn't do lookups at
all. It registers itself as "interested" in a service and then gets
notifications of when this service is available. So the above could look
like;
provider.addInterestListener( whatever, this );
:
:
if( m_Available )
{
m_Service.useService();
}
else
{
// some necessary backup...
}
public void serviceAvailable( InterestEvent event )
{
if( whatever.equals( event.getLookupRole() )
{
m_Service = event.getService();
m_Available = true;
}
}
public void serviceUnavailable( InterestEvent event )
{
if( whatever.equals( event.getLookupRole() )
{
m_Service = null;
m_Available = false;
}
}
There is of course a lot more to it, and better names can be used, and 100
other implementation details.
Most programmers would call the above an overkill for most applications, since
they "know" the execution will be local. That may not be true later.
But please do come over to [EMAIL PROTECTED] with these kind of discussion. It
belongs more there, than in the [EMAIL PROTECTED]
Cheers
Niclas
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