Re: Looking for a pattern
Bilz wrote:
On Oct 31, 4:32 pm, Roedy Green <see_webs...@mindprod.com.invalid>
wrote:
On Wed, 31 Oct 2007 19:30:23 -0000, Bilz <BrianGeni...@gmail.com>
wrote, quoted or indirectly quoted someone who said :
Now we have a new requirement... run multiple instances of the
software in the same application space with different configurations.
<sarcasm>shocking</sarcasm>
You need some sort of factory to create your service provider. Perhaps
it can cache them, and reuse an existing provider if its set of
configurations have already been used before.
You create a key class that contains the various distinguishing
initialisation parameters, then a hashCode that xors the various
fields. Then use this key class to create index into your HashMap
cache of pre-built providers.
--
Roedy Green Canadian Mind Products
The Java Glossaryhttp://mindprod.com
Ok, that is fine... but how does all of the classes get the key? Do
you pass them in to every constructor, and keep track of the key all
the way down the object graph? This is what I am trying to avoid...
though I can't think of a way how.
Even if you pass a key all the way down, you'd be better off passing the
actual object all the way down, then you eliminate the need to do a map
lookup.
If you're using Java, and the partition aligns nicely with threads, you
can use ThreadLocal variables...
Also, look into the Dependency Injection pattern, as well as other forms
of Inversion of Control.
You don't have to pass it into every constructor, but just make sure
that your object relationships have everything you need to get the
configuration you care about.
As a matter of fact, you should probably have your configuration object
instantiate most of the objects (think of it as a factory), and have it
connect them to each other.
--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>