Spring is a non-invasive framework

Spring is a non-invasive framework. This is the key departure from most previous frameworks. Whereas traditional frameworks such as EJB or Apache Avalon force application code to be aware of the framework, implementing framework-specific interfaces or extending framework- specific classes, Spring aims to minimize the dependence of application code on the framework. Thus Spring can configure application objects that don't import Spring APIs; it can even be used to configure many legacy classes that were written without any knowledge of Spring. This has many benefits. For example:

Application code written as part of a Spring application can be run without Spring or any other container.

Lock-in to Spring is minimized. For example, you could migrate to another lightweight container, or possibly even reuse application objects in an EJB 3.0 EJB container, which supports a subset of Spring's Dependency Injection capability.

Migration to future versions of Spring is easier. The less your code depends on the framework, the greater the decoupling between the implementation of your application and that of the framework. Thus the implementation of Spring can change significantly without breaking your code, allowing the framework to be improved while preserving backward compatibility.

Of course in some areas, such as the web framework, it's impossible to avoid application code depending on the framework. But Spring consistently attempts to reach the non-invasive ideal where configuration management is concerned.