8.4.2 Client view of a message-driven bean
Unlike session and entity beans, message-driven beans do not expose home or component interfaces. A client is not able to locate instances of an MDB and invoke methods on it directly.
The only manner in which a client can interact with an MDB is to send a message to the destination or endpoint for which the MDB is the listener. The EJB container is responsible for invoking an instance of the MDB as a result of the arrival of a message. From the client's perspective, the existence of the MDB is completely transparent.
Figure 8-13 Client view of a message-driven bean
A bean provider developing a message-driven bean must provide a message-driven bean implementation class. This class must implement, directly or indirectly, the javax.ejb.MessageDrivenBean interface and a message listener interface. It must also provide an ejbCreate method implementation.