The Open Source Zone

Excalibur is an open source software project of The Apache Software Foundation. Our primary product is a lightweight, embeddable Inversion of Control container named Fortress that is written in java.

Inversion of control, also known as the hollywood principle ("don't call us, we'll call you") is a simple put powerful concept. The idea is that we don't " wire up" all the pieces that make up an application (the "components") by writing lots of this-component-uses-that-one-like-so code, nor do we use some kind of lookup directory (like JNDI, for example) where each component decides what components to interact with itself. Instead, we instruct a smart piece of software, the container, to tell the components how to interact.

Fortress (and also its predecessor, "ECM") is such a container. It is lightweight, by which we mean that it doesn't need a lot of resources, take a lot of disk or memory, or impose all sorts of demans on its environment. Fortress is also embeddable, by which we mean that you can use fortress inside just about every java environment. More concretely, you can use it as the basis of a large standalone development platform (like the Keel project), at the core of a servlet-based web application (like Cocoon) or even as the basis of a GUI application (like GuiApp).

Fortress knows how to manage components that have been developed using a rigid lifecycle contract called Avalon- Framework. In the next upcoming release, fortress will also be able to manage ordinary javabeans, and support for other kinds of Inversion of Control are planned.

Besides providing fortress, excalibur also provides a small library of very useful components. We also distribute some of the libraries used to build fortress (and some other containers) seperately. This selection of libraries is called containerkit.