Apache Geronimo
Like an enterprise operating system, Geronimo is built on a kernel—a microkernel that lays the foundation for everything above it. Geronimo's kernel is Java EE agnostic. Its sole purpose is to manage Geronimo's building blocks. Geronimo is marked by an architectural design that is based on the concept of Inversion of Control (IoC) (sometimes called Dependency Injection), which means that the kernel has no direct dependency on any of its components. The kernel is a framework for services that controls the service life cycle and registry. The kernel is based on Java EE. It works with Java EE services and components to build specific configurations—one of which is a full Java EE solution stack. A majority of the Geronimo services are added and configured through GBeans to become a part of the overall application server. A "GBean" is the interface that connects the component to the kernel. Each GBean can maintain state, depend on, and interrelate with other GBeans, and operate on events from the kernel and other GBeans. The GBeans interface makes it possible to switch between two servlet containers, for example Jetty or Tomcat, without affecting the whole architecture using a GBeans interface. This flexible architecture makes it possible for the Geronimo developers to integrate several existing field-tested open source software projects. Here a list of the open source components that are included in the Geronimo project.
Components
Apache Geronimo is an open source application server developed by the Apache Software Foundation and distributed under the Apache license.