Hibernate team member Emmanuel Bernard recently wrote on the issues with the ActiveRecord pattern and statically typed languages like Java. He states that:
...Dynamic languages (and to a certain extend AOP) have the nice ability to decorate an object with additional features on the fly, without linking it "the hard way": you can then easily reuse your domain classes out of the persistence context...
Bernard goes on to say that this lack of ability with statically typed languages has given rise to DAO (DAL in .Net land) patterns to separate data representation and persistence technology. The solution to this in the statically typed world in his opinion is dynamic DAO generation which is already being done in JBoss Seam from generics and GORM in Grails.
Grails project lead Graeme Rocher adds:
...With GORM not forcing you to extend any base class and being totally unobtrusive this is all possible. The reality is Java frameworks force you to have a DAO layer, its not out of choice that they exist. Still this is not an insurmountable problem, I'm surprised there aren't more AOP based solutions around. In the meantime GORM is solving real problems...