Using annotations in JavaBeans is an elegant way of defining validation rules in a declarative way. Apart from MyFaces ExtVal there are other projects that introduced declarative validation, such as the Hibernate Validator and the Bean Validation Framework for Spring. Some framework developers realized that it would be a good idea to standardize this type of validation. This led to the Bean Validation specification that was developed as JSR 303 in the Java Community Process. Accordingly, Bean Validation will be a standard part of Java EE 6, but it can be used in Java EE 5 by manually including a Bean Validation implementation.
One of the benefits of having an official standard for validation is that various user interface frameworks can implement support for this type of validation. For example, JavaServer Faces 2.0 will have support for Bean Validation embedded in it, and other UI frameworks will probably follow.
But at the moment, we’re still building Java EE 5 and...