Inversion of control container (dependency injection)
Central to the Spring Framework is its inversion of control (IoC) container, which provides a consistent means of configuring and managing Java objects using reflection. The container is responsible for managing object lifecycles of specific objects: creating these objects, calling their initialization methods, and configuring these objects by wiring them together.
Objects created by the container are also called managed objects or beans. The container can be configured by loading XML files or detecting specific Java annotations on configuration classes. These data sources contain the bean definitions that provide the information required to create the beans.
Objects can be obtained by means of either dependency lookup or dependency injection.[11] Dependency lookup is a pattern where a caller asks the container object for an object with a specific name or of a specific type. Dependency injection is a pattern where the container passes objects by name to other objects, via either constructors, properties, or factory methods.
In many cases one need not use the container when using other parts of the Spring Framework, although using it will likely make an application easier to configure and customize. The Spring container provides a consistent mechanism to configure applications and integrates with almost all Java environments, from small-scale applications to large enterprise applications.
The container can be turned into a partially compliant EJB 3.0 container by means of the Pitchfork project. Some[who?] criticize the Spring Framework for not complying with standards.[12] However, SpringSource doesn't see EJB 3 compliance as a major goal, and claims that the Spring Framework and the container allow for more powerful programming models.[13] You do not create an object, but describe how they should be created, by defining it in the Spring configuration file. You do not call services and components, but tell which services and components must be called, by defining them in the Spring configuration files. This makes the code easy to maintain and easier to test through IoC.