INTERVIEW QUESTIONS J2EE EJB DETAILS

Question: Why an onMessage call in Message-driven bean is always a seperate transaction?

Answer: EJB 2.0 specification: "An onMessage call is always a separate transaction, because there is never a transaction in progress when the method is called."

When a message arrives, it is passed to the Message Driven Bean through the onMessage() method, that is where the business logic goes.

Since there is no guarantee when the method is called and when the message will be processed, is the container that is responsible of managing the environment, including transactions ?

Hence it is always carried as a seperate Transaction.

Submitted by Sagar GV ([email protected])


__________________________

The container invokes a message driven bean method
with its transaction attribute set to Required with a
valid transaction context. Since there is no client
transaction context available for a message-driven
bean, the container automatically starts a new
transaction before the dequeuing of the JMS message
which is before the invocation of the onMessage
method. The container automatically enlists the
resource manager associated with the arriving message
and all the resource managers accessed by the
onMessage method with the transaction. If the
onMessage method invokes other enterprise beans, the
container propagates the transaction context with the
invocation. Finally, it attempts to commit the
transaction when the onMessage method has completed.
In case the onMessage method does not successfully
complete, the transaction is rolled back by the
container and typical JMS message redelivery semantics
apply.

Submitted by Anuya Inamdar. ([email protected])

EJB 2.0 specification: "An onMessage call is always a separate transaction, because there is never a transaction in progress when the method is called."

When a message arrives, it is passed to the Message Driven Bean through the onMessage() method, that is where the business logic goes.

Since there is no guarantee when the method is called and when the message will be processed, is the container that is responsible of managing the environment, including transactions ?

Hence it is always carried as a seperate Transaction.

Submitted by Sagar GV ([email protected])


__________________________

The container invokes a message driven bean method
with its transaction attribute set to Required with a
valid transaction context. Since there is no client
transaction context available for a message-driven
bean, the container automatically starts a new
transaction before the dequeuing of the JMS message
which is before the invocation of the onMessage
method. The container automatically enlists the
resource manager associated with the arriving message
and all the resource managers accessed by the
onMessage method with the transaction. If the
onMessage method invokes other enterprise beans, the
container propagates the transaction context with the
invocation. Finally, it attempts to commit the
transaction when the onMessage method has completed.
In case the onMessage method does not successfully
complete, the transaction is rolled back by the
container and typical JMS message redelivery semantics
apply.

Submitted by Anuya Inamdar. ([email protected]) Source: CoolInterview.com

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