[Springframework-developer] AOP changes

[Rod J. <rod...@in...>]

All,

I've made some further AOP changes, partly to allow for further CGLIB
optimization, but principally to allow for a cleaner approach to pooling
etc.

The InvokerInterceptor is now gone. The old approach of the terminal
interceptor invoking the target object has been replaced by this behaviour
in the MethodInvocation itself. Of course other "terminal" invokers such as
the EJB invokers will continue to work just fine as they don't call proceed.

Other MethodInvocation implementations--CGLIB etc.--can have their own
invocation behavior, for greater efficiency. (We don't want to end up
calling Method.invoke with CGLIB.)

Instead, there's a new interface: org.springframework.aop.TargetSource will
identifies the "this" part of the joinpoint. (Of course this kind of thing
isn't "classic" AOP and I don't think it can be done with AspectJ. But it's
useful.) Normally the implementation is SingletonTargetSource, which caches
a target. However, PrototypeInvokerInterceptor etc. are now in the
aop.target package as PrototypeTargetSource, ThreadLocalTargetSource etc. A
TargetSource or target can be used as the final name in an interceptor
chain, as a target could formerly, so there shouldn't be that much impact on
code.

The only effect on your code should be:
- if you use the PrototypeInvokerInterceptor, PoolingInvokerInterceptor or
ThreadLocalInvokerInterceptor, in which case you need to move that bean
definition to the corresponding TargetSource, which will be configured
similarly.
- if you created AOP proxies programmatically using an InvokerInterceptor.
This is no longer necessary.
- if you've subclassed or otherwise depended on the internals of some of the
AOP classes.

Note that it's no longer necessary to add an InvokerInterceptor as the last
advisor when creating a proxy programmatically: a nice feature.

So for:

ProxyFactory p = new ProxyFactory(target);
p.addInterceptor(0, new DebugInterceptor());

Can omit the index (0) in the second line.

In the second line now we can add interceptors in order without bothering
about the index (although this version will still work). Because there's no
InvokerInterceptor, there are no longer any special requirements for the
last interceptor.

Regards,
Rod