MDB configuration in JBoss4
The default configuration of an MDB in JBoss4 is backwardly compatible with jboss-3.2.x. That is, it uses the EJB2.0 notions rather EJB2.1 configuration.
This allows people to easily migrate from JBoss-3.2.x to JBoss4.
You can find this configuration in conf/standardjboss.xml, search for "message-driven-bean".
EJB2.1 inflow driven bean
From EJB2.1 in JBoss4, you can configure an MDB to use JCA message inflow with activation-config parameters.
This can also be found in conf/standardjboss.xml, search for "message-inflow-driven-bean".
EJB2.1 and JMS
There is a convenience configuration for JMS in EJB2.1 when using JBoss's inbound jms resource adapter. This configuration has defaults similar to what is provided in the EJB2.0/jboss-3.2.x MDB config.
You will find this "commented out" in conf/standardjboss.xml
A note about JBoss's inbound jms resource adapter
The inbound jms message inflow provided by deploy/jms/jmsra.rar is currently experimental.
It hasn't had any serious stress testing
All the corner cases of the configuration options have not been tested
DO NOT USE IT IN PRODUCTION UNLESS YOU DO SOME SERIOUS TESTING FIRST
MDB - message driven beans
JCA message inflow - EJB2.1 style message inflow
JMS message inflow - JBoss's inbound jms resource adapter
JMS provider - Configuring the jms implementation