Something about POJOS in Spring 2.5.6 Ducument

 POJOs are essentially plain old Java classes free from any contract usually enforced by a framework or component architecture through subclassing or the implementation of interfaces. POJOs are plain old objects that are free from such constraints, making object-oriented programming possible once again. When you are working with Spring, the domain objects and services you implement will be POJOs. In fact, almost everything you implement should be a POJO. If it's not, you should be sure to ask yourself why that is.