Adobe Flex is one of the most widely used client technologies for building rich applications and Spring 3 is one of the most popular Java application frameworks. These two technologies make a great combination for building enterprise applications with a modern-looking and rich user interface.
There are various options to integrate them, and each has its pros and cons, such as Web/REST services and the Spring-Flex project promoted by Adobe and SpringSource. There are lots of articles and resources about them. Here, I will focus on an alternative approach using the open-source project GraniteDS.