MDBs must be run within an EJB container. Depending on the architecture of your app, this may be an excessive requirement, especially if you aren't use any other EJBs and do not require the features of a full-blown EJB container. Message-driven POJOs, on the other hand, can run anywhere, even (as shown here) in a simple main() method. The only requirement is an ActiveMQ message queue.
MDBs require that you implement the lifecycle methods of javax.ejb.MessageDrivenBean. Often these lifecycle methods aren't needed and are left as empty implementations. This isn't a real problem, except that it's simply unnecessary.
Although it may not be apparent from the simple HelloBean example, message-driven POJOs can take full advantage of the dependency injection and AOP support offered by Spring (including Spring's support for declarative transactions and Acegi's support for declarative security). In short, you can do anything with the POJO that you can do with any other bean in a Spring context.
The XML used to declare a message-driven POJO is slightly more verbose then for an MDB. You should, however, keep in mind that you'll only need to declare one JCAContainer bean, regardless of how many message-driven POJOs your application has.
MDBs require that you implement the lifecycle methods of javax.ejb.MessageDrivenBean. Often these lifecycle methods aren't needed and are left as empty implementations. This isn't a real problem, except that it's simply unnecessary.
Although it may not be apparent from the simple HelloBean example, message-driven POJOs can take full advantage of the dependency injection and AOP support offered by Spring (including Spring's support for declarative transactions and Acegi's support for declarative security). In short, you can do anything with the POJO that you can do with any other bean in a Spring context.
The XML used to declare a message-driven POJO is slightly more verbose then for an MDB. You should, however, keep in mind that you'll only need to declare one JCAContainer bean, regardless of how many message-driven POJOs your application has.
