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by Jon Tirsen.
Original Post: PicoContainer / NanoContainer
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The founders of the project are Paul (AltRMI, Enterprise Object Broker) and Aslak (XDoclet, MiddleGen). Actually they pair-programmed most of it at Paul's place and a lot of beer was involved. The end result: a neat, simplistic and wonderfully TDDed piece of work. Joe (SiteMesh, QDox), my unit-testing guru, is also in on it.
It's basically an Inversion-of-Control-container/framework/micro-kernel. Pico will be the simplistic micro-kernel and Nano will be a bunch of containers serving different purposes (most built on top of Pico).
I'm not an IoC-expert by any means, and, well, I didn't know much about it before chatting with Paul and Aslak. The cool (and quite controversial) thing is that Pico (at least by default) implements style 3 IoC, which means constructors are used to define dependencies. Smart!
I will implement some Nanning support in Nano so that aspects can define dependencies on services and the container will resolve them properly, the aspects will also be able to aspectify the components transparently. The details are far from finalized, just a bunch of semi-digested ideas. I'll give you a couple of use-cases though. An aspect implementing transparent persistence with Prevayler could retrieve it's Prevayler-instance just by declaring it in its constructor:
public class PrevaylerAspect {
public PrevaylerAspect(Prevayler prevayler) { /* ... */ }
/* ... */
}
A declarative transaction aspect could declare it's dependency on a TransactionManager by:
public class TransactionAspect {
public TransactionAspect(TransactionManager transactionManager) { /* ... */ }
/* ... */
}
Put these aspects along with their services in a container, Pico does it's work and all components are properly assembled:
PicoContainer pico = new HierarchicalPicoContainer.Default();
pico.registerComponent(RemoteTransactionManagerImpl.class);
pico.registerComponent(PicoPrevayler.class);
pico.registerComponent(PrevaylerAspect.class);
pico.registerComponent(TransactionAspect.class);
pico.start();
Neat and simple. No XML, no runtime attributes, no fuss.
Another great thing is that it's brilliant to mock-test the things. Say you want to mock-test your TransactionAspect to see that it actually demarcates it's transactions properly:
MockTransactionManager mockTransactionManager = new MockTransactionManager();
// ...set up expectations and so forth...
TransactionAspect transactionAspect = new TransactionAspect(mockTransactionManager);
AspectSystem aspectSystem = new AspectSystem();
aspectSystem.addAspect(transactionAspect);
TestObject testObject = (TestObject) aspectSystem.newInstance(TestObject.class);
// ...run your tests on your testObject...
mockTransactionManager.verify();
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