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Java Survival Kit

Bean Overview

A Spring IoC container manages one or more beans. These beans are created with the configuration metadata that you supply to the container (for example, in the form of XML definitions).

Within the container itself, these bean definitions are represented as BeanDefinition objects, which contain (among other information) the following metadata:

  • A package-qualified class name: typically, the actual implementation class of the bean being defined.
  • Bean behavioral configuration elements, which state how the bean should behave in the container (scope, lifecycle callbacks, and so forth).
  • References to other beans that are needed for the bean to do its work. These references are also called collaborators or dependencies.
  • Other configuration settings to set in the newly created object — for example, the size limit of the pool or the number of connections to use in a bean that manages a connection pool.

In addition to bean definitions that contain information on how to create a specific bean, the ApplicationContext implementations also permit the registration of existing objects that are created outside the container (by users). This is done by accessing the ApplicationContext’s BeanFactory through the getBeanFactory() method, which returns the DefaultListableBeanFactory implementation. DefaultListableBeanFactory supports this registration through the registerSingleton(..) and registerBeanDefinition(..) methods. However, typical applications work solely with beans defined through regular bean definition metadata.