AspectJ2EE = AOP + J2EE Towards an Aspect Based, Programmable and Extensible Middleware Framework

摘要

J2EE is a middleware architecture augmented with supporting tools for developing large scale client/server and multi-tier applications. J2EE uses Enterprise JavaBeans as its component model. The realization of these components by a J2EE application server can be conceptually decomposed into distinct aspects such as persistence, transaction management, security, and load balancing. However, current servers do not employ aspect-oriented programming in their implementation. In this paper, we describe a new aspect language, AspectJ2EE, geared towards the generalized implementation of J2EE application servers, and applications within this framework. AspectJ2EE can be easily employed to extend the fixed set of services that these servers provide with new services such as logging and performance monitoring. Even tier-cutting concerns like encryption, data compression, and memoization can be added while avoiding the drags of cross-cutting and scattered code. AspectJ2EE is less general (and hence less complicated) than AspectJ, yet demon-strably powerful enough for the systematic development of large scale (and distributed) applications. The introduction of parameterized aspects makes aspects in AspectJ2EE more flexible and reusable than aspects in AspectJ. AspectJ2EE also generalizes the process of binding services to user applications in the application server into a novel deploy-time weaving of aspects. Deploy-time weaving is superior to traditional weaving mechanisms, in that it preserves the object model, has a better management of aspect scope, and presents a more understandable and maintainable semantic model.