Spring is the most popular open source Java application Framework. Most of the existing frameworks like Struts or Hibernate take care of one layer or a part of the application development.
As Struts take care of MVC model, Hibernate provides ease of working with databases. However, Spring Framework combines all the industry standard framework approaches (e.g. Struts and Hibernate) into one bundle.
Spring provides Dependency Injection, Aspect Oriented Programming and support for unit testing. This gives the developer time to work on main business logic rather than worrying about non-application code. Spring makes the application development fast and increases the productivity of developers.