The Hundred-Kilobyte Kernel (HK2) is the lightweight and extensible kernel of GlassFish Server. HK2 consists of the following technologies:
Module subsystem. The HK2 module subsystem provides isolation between components of the GlassFish Server. The HK2 module subsystem is compatible with existing technologies such as the OSGi framework.
Component model. The HK2 component model eases the development of components that are also services. GlassFish Server discovers these components automatically and dynamically. HK2 components use injection of dependencies to express dependencies on other components. GlassFish Server provides two-way mappings between the services of an HK2 component and OSGi services.
For more information, see Chapter 2, Writing HK2 Components.