Head First EJB

Chapter 8. Message-Driven Beans: Getting the Message

It’s fun to receive messages. Not as much fun as, say, getting that EBay package with the genuine Smurf™ lamp, but fun and efficient nonetheless. Imagine if you sent your order to EBay, and you couldn’t leave your house until the package was delivered. That’s what it’s like with Session and Entity beans, because there’s all calls to a bean’s client interface (home, component, local, Remote, doesn’t matter) are synchronous. But with message-driven beans, the client makes a message and sends it to a messaging service. Then the client walks away. Later, the messaging service sends the Container the message, and the Container give it to a message-driven bean.

Objectives: Message-Driven Beans

Official:		What it really means:
10.1	Identify correct and incorrect statements or examples about the client view, and lifecycle, of a message-driven bean.	You have to know that message-driven beans don’t have clients! That means no home interface, no component interface, and no issues of local vs. Remote. Of course message-driven beans do have a caller, but that’s the Container. And we don’t consider the Container a client. The Container is the boss, not the customer. Message-driven beans have a very simply lifecycle—if you know how stateless session beans work, you know how message-driven beans work. The only different is that instead of bringing a bean ...