I am coming back to Java from Ruby and ActiveRecord and want to use something as easy as ActiveRecord in Ruby. What options do I have?
I like JPA myself (Java Persistence API). Easy to configure and with the right tools you can generate the database from classes or generate the classes from the database. It's easy to configure your classes with the annotations that you can use.
I use the OpenJPA implementation myself.
It'll probably some sort of Object Relational Mapping framework you end up using. Grails (a Java Rails like framework) has GORM:
If you're not using a web framework like that then it'll prob. be some sort of ORM framework - Hibernate, OpenJPA etc...
If you don't want to do the full heavyweight ORM way then look at something like MyBatis (used to be iBatis) which has SQLMaps:
Hibernate provides very nice ActiveRecord-like access. There are tools to reverse-engineer models from the database. I keep it simple and it works well for me.
There is a project that a colleague recently released called ActiveJDBC that is an implementation of ActiveRecord for Java.