The Spring Framework (or Spring for short) is an open source application framework for the Java platform. The first version was written by Rod Johnson, who first released it with the publication of his book Expert One-on-One J2EE Design and Development (Wrox Press, October 2002). A port is available for the .NET Framework[1]. The Spring 1.2.6 framework won a Jolt productivity award in 2006 [2].
Although the Spring Framework does not enforce any specific programming model, it has become popular in the Java community as an alternative, replacement, or even addition to the Enterprise JavaBean (EJB) model. By design, the framework offers a lot of freedom to Java developers yet provides well documented and easy-to-use solutions for common practices in the industry.
While the core features of the Spring Framework can be used by any Java application, there are many extensions and improvements for building web-based applications on top of the Java Enterprise platform. Spring is popular because of this, and is recognized by vendors as a strategically important framework. [3]
The framework was first released under the Apache 2.0 license in June 2003. The first milestone release, 1.0, was released in March 2004, with further milestone releases in September 2004 and March 2005. Current version is 2.5.6.

http://en.wikipedia.org/wiki/Spring_framework
http://www.springsource.org/