SERVICE LOCATOR ?? Is it really an interesting Design pattern??

Hi everybody,
i've a problem with the J2EE Design Pattern "Services locator" (it's a singleton).
It is said that by making use of a Service Locator we can :
- hide to the client the complexities of initial context creation, EJB home object lookup,and EJB objectre-creation.
- multiple clients can reuse the Service Locator object to reduce code complexity, provide a single point of control, and improve performance by providing a caching facility.
But i would like to understand at which side should that service locator object reside??!!??
If it is at server side then the clients need well an initial context in order to make a lookup on that object.
Conclusion :
the service locator doesn't hide the complexities of initial context!!
Furthermore the client has to perform a look-up on that service locator object!! The only advantage left is caching facility.
If it is at client side, each client needs his own services locator object
Conclusion :
multiple client don't reuse the same service locator. What's the advantage to be a singleton ???
There is certainly something that i don't understand so help me please!! Thanks.

Hi Yves,
But i would like to understand at which side should
that service locator object reside??!!??
If it is at client side, each client needs his own
services locator object
Conclusion :
multiple client don't reuse the same service locator.
What's the advantage to be a singleton ???The service locator resides on the client side and is implemented as
a singleton. Since it is possible that there could be multiple
class loaders/JVMs on the client side, and therefore, multiple
instances of the "singleton" service locator. This is typical
in a distributed environment (e.g. servlets/JSPs in a web-tier
cluster using service locator). Thus service locator is not
a truly "distributed singleton" object. But, the empahsis
is to design the service locator such that it does not hold
any state that needs to be replicated across multiple
instances across different JVMs as mentioned. Thus, there
is no need for multiple clients to use the "same" service locator,
but still the benefits of implementing this pattern is realized.
By making it a singleton, and keeping it from holding state
that needs to be replicated, we realize the benefits of this pattern.
You may also want to visit the J2EE Pattern interest list
and see these relevant discussions :
Topic: Service Locator and passivation
http://archives.java.sun.com/cgi-bin/wa?A2=ind0106&L=j2eepatterns-interest&F=&S=&P=1026
Topic: Caching EJBHome interfaces
http://archives.java.sun.com/cgi-bin/wa?A2=ind0106&L=j2eepatterns-interest&F=&S=&P=9226
Topic: Using Service Locator for Data Source caching
http://archives.java.sun.com/cgi-bin/wa?A1=ind0106&L=j2eepatterns-interest#31
hope this helps,
thanks,
-deepak

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SERVICE LOCATOR ?? Is it really an interesting Design pattern??

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