Spring is a J2EE application framework based on code published in the book "ExpertOneonOneJ2EE" by Rod Johnson. Spring includes: 1) Powerful JavaBeans-based configuration management. 2) JDBC abstraction layer. 3) Abstraction layer for transaction management. 4) Flexible MVC web application framework. 5) AOP functionality, fully integrated into Spring configuration management. You can use all of Spring's functionality in any J2EE server, or outside a server.