If you have been using the Spring Framework for some time, you will be aware that Spring has undergone two major revisions: Spring 2.0, released in October 2006, and Spring 2.5, released in November 2007. It is now time for a third overhaul resulting in Spring 3.0.
The entire framework code has been revised to take advantage of Java 5 features like generics, varargs and other language improvements. We have done our best to still keep the code backwards compatible. We now have consistent use of generic Collections and Maps, consistent use of generified FactoryBeans, and also consistent resolution of bridge methods in the Spring AOP API. Generified ApplicationListeners automatically receive specific event types only. All callback interfaces such as TransactionCallback and HibernateCallback declare a generic result value now. Overall, the Spring core codebase is now freshly revised and optimized for Java 5.
Spring's TaskExecutor abstraction has been updated for close integration with Java 5's java.util.concurrent facilities. We provide first-class support for Callables and Futures now, as well as ExecutorService adapters, ThreadFactory integration, etc. This has been aligned with JSR-236 (Concurrency Utilities for Java EE 6) as far as possible. Furthermore, we provide support for asynchronous method invocations through the use of the new @Async annotation (or EJB 3.1's @Asynchronous annotation).