In accordance with modern development methods JBoss Microcontainer supports POJO configuration via annotations and/or deployment descriptors. The decision to use one or the other depends on what you are trying to achieve. If there is a sensible default configuration for your POJOs then it may be worthwhile defining this using annotations so that users do not have to maintain a separate deployment descriptor. Since annotations are overriden by deployment descriptors at runtime it is always possible for users to change the default configuration using a descriptor if necessary.

If there is no sensible default configuration then it may be worthwhile using a deployment descriptor instead of annotations. This keeps the source code free of potentially redundant information and allows for easy customization since the initial deployment descriptor acts as a template for further changes.

Sometimes a mixture of annotations and a deployment descriptor is best. It's up to you to discover what makes most sense for your particular situation.