I'm trying to embed Axis2 into a clustered environment and have found that
the code doesn't neatly fit into the existing extensible handler chain.
The scenario I'm trying to support is non-Axis2 code which can decide to
override the target address which is dispatched to based on some
clustering information. This could either recognise that the address is
local, allowing a local optimisation or decide to workload balance to
another member of the defined cluster.
This doesn't really fit into the handler chain because the decision on
which transport to use is (and should be) taken before the handler chain
is selected and invoked. This is important because it allows different
chains to be executed depending on the transport - e.g.a local-only
transport might not need to encrypt the message.
In order to support this scenario I'm proposing that we add pluggable
TargetResolvers. They would be registered in axis2.xml and be available
from the AxisConfiguration object. The OperationClient would then invoke
the chain prior to selecting the transport and invoking the AxisEngine
(and hence the handler chain). This would also be done in the
MessageReceivers prior to the AxisEngine.send() so any non-anonymous
ReplyTo is treated properly.
A TargetResolver would simply be passed the MessageContext which it could
then modify appropriately.
Thus we'd have:
interface TargetResolver{
/**
* resolveTarget examines the MessageContext and updates the
MessageContext
* in order to resolve the target.
*/
void resolveTarget(MessageContext mc);
}
an additional section in axis2.xml looking like:
<targetResolvers>
<targetResolver name="LocalOptimisationResolver" class="..."/>
...
</targetResolvers>
and a new method on AxisConfiguration:
/**
* getTargetResolverChain returns and instance of
* TargetResolver which iterates over the registered
* TargetResolvers, calling each one in turn when
* resolveTarget is called
*/
public TargetResolver getTargetResolverChain();
I'll have code for this ready in a few days.
Questions/Comments?
David
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