JBoss

Seam is a "lightweight framework" because it promotes the use of POJO (plain old Java objects) as service components. There are no framework interfaces or abstract classes to "hook" components into the application. The question, of course, is how do those POJOs interact with each other to form an application? How do they interact with container services (e.g., the database persistence service)?

Seam wires POJO components together using a popular design pattern known as "dependency injection" (DI). Under this pattern, the Seam framework manages the lifecyle of all the components. When a component needs to use another, it declares this dependency to Seam using annotations. Seam determines where to get this dependent component based on the application's current state and "injects" it into the asking component.
Expanding on the dependency injection concept, a Seam component A can also create another component B and "outjects" the created component B back to Seam for other components, such as C, to use later.