Dependency injection removes the responsibility for object creation and object linking from the objects themselves to a factory. The factory is often provided by an Inversion of Control (IoC) container. For an overview of of Inversion of Control containers and the Dependency Injection pattern, please see Martin Fowler's article.
Spring
By default, the framework uses Spring for dependency injection. You may also use Spring to inject objects into your own applications. Besides Spring, there are other containers that you can use, such as Pico.
WebWork/XWork integrated IoC Container
The WebWork/XWork IoC container utilized by WebWork 2.1 is not supported by Action 2.