+1
Maybe it should be noted that the examples in proposal B and C are just pseudo code to make it more readable.
On 21.10.2011, at 20:05, Nigel Deakin wrote:
> I have logged the following JIRA issue
> http://java.net/jira/browse/JMS_SPEC-54
>
> This is a companion issue to http://java.net/jira/browse/JMS_SPEC-30 (Define mandatory activation config properties for
> JMS MDBs) which covers standardising how you can configure the queue or topic on which a MDB consumes messages.
>
> This isn't actually a JMS issue, it's a MDB issue, and I've already reviewed this in principle with the Java EE and EJB
> spec leads, but I'd like to run this past the JMS expert group before submitting this as a formal request to the EJB
> expert group.
>
> The issue description is below, but it may be easier to read the formatted version using the JIRA link above.
>
> This proposal suggests some new XML element and annotation attribute names: I expect these will be subject to change.
>
> As always, comments welcome (including those of the +1 variety...). Does anyone think I've missed anything?
>
> Nigel
>
>
> Define a standard way to configure the destination on which a MDB consumes messages
> -----------------------------------------------------------------------------------
>
> This is a request for the JMS and/or EJB specifications to improve the way in which specify how an application or
> deployer may specify the destination from which a JMS message-driven bean to receive messages. There are several
> significant omissions from the specification which need to be rectified.
> Although MDBs are specified in the EJB specification, this request should be considered first by the JMS 2.0 expert
> group who may then want to raise it with the EJB 3.2 expert group.
> h3. Review of existing specification (EJB 3.1)
>
> In the EJB 3.1 specification, Section 16.9 "Message Destination References" states that the destination used by a JMS
> message-driven bean can be specified using the {{<message-destination-link>}} element of the <message-driven> element in
> {{ejb-jar.xml}}:
>
> {noformat}
> <message-driven>
> <ejb-name>ExpenseProcessing</ejb-name>
> <ejb-class>com.wombat.empl.ExpenseProcessingBean</ejb-class>
> <messaging-type>javax.jms.MessageListener</messaging-type>
> ...
> <message-destination-type>javax.jms.Queue</message-destination-type>
> <message-destination-link>ExpenseProcessingQueue</message-destination-link>
> ...
> </message-driven>
> {noformat}
>
> h3. Issues with the existing specification
>
> This raises the following questions:
>
> h4. 1. What is <message-destination-link>?
>
> The {{<message-destination-link>}} element defines the destination from which the MDB consumes messages in terms of a
> "message destination reference".
> The purpose of "message destination references" is to allow an application which sends messages to a particular
> destination and also consumes from the same destination to inform the deployer of this fact without having to actually
> specify the name (or JNDI name) of the destination.
> As stated above, a MDB can specify the "message destination reference" of the destination from which it consumes
> messages using a {{<message-destination-link>}} element under the <message-driven> element. Another component (e.g. a
> session bean or another MDB) can specify the destination to which it sends messages using a
> {{<message-destination-link>}} element under a {{<message-destination-ref>}} element. If these two elements contain the
> same string then the deployer knows they refer to the same queue or topic.
>
> A message destination reference is not the JNDI name of the queue or topic. It is just a logical name. It can be mapped
> to an actual JNDI name using the {{<assembly-descriptor>}} element in {{ejb-jar.xml}} as follows:
>
> Here's how {{ejb-jar.xml}} could be used to define a MDB as consuming messages from a "message destination reference"
> called {{MsgBeanInQueue}} which was mapped to a JNDI name {{jms/inboundQueue}}:
>
> {noformat}
> <ejb-jar>
> <enterprise-beans>
> <message-driven>
> <display-name>MDB1</display-name>
> <ejb-name>MessageBean</ejb-name>
> <messaging-type>javax.jms.MessageListener</messaging-type>
> <transaction-type>Container</transaction-type>
> <message-destination-type>javax.jms.Queue</message-destination-type>
> <message-destination-link>MsgBeanInQueue</message-destination-link>
> </message-driven>
> </enterprise-beans>
> <assembly-descriptor>
> <message-destination>
> <lookup-name>jms/inboundQueue</lookup-name> <!---
> <message-destination-name>MsgBeanInQueue</message-destination-name>
> </message-destination>
> </assembly-descriptor>
> </ejb-jar> {noformat}
>
> A message destination reference can typically also be mapped to an actual JNDI name using the
> application-server-specific deployment descriptor, though by definition this is beyond the scope of the EJB specification.
>
> h4. 2. Is that the only way you can define the destination on which a MDB consumes messages in ejb-jar.xml? Can you
> define its JNDI name directly without bothering with references?
>
> No, the EJB specification doesn't mention any way to define the destination in {{ejb-jar.xml}} apart from using the
> {{<message-destination-link>}} element of {{ejb-jar.xml}}. In particular it doesn't define any way to define its JNDI
> name directly, analogous to using either the JNDI API or a {{_at_Resource(lookup="jms/foo")}} declaration for managed
> connections.
>
> h4. 3. Can I define the message destination reference for a MDB using annotation?
>
> No, there is equivalent to {{<message-destination-link>}} using annotation.
>
> h4. 4. Can I define the JNDI name of the destination on which a MDB consumes messages directly using annotation?
>
> No, there is no way to define this using annotation, analogous to using a {{_at_Resource(lookup="jms/foo")}} declaration
> when using the JMS API directly.
>
> So, what seems to be missing?
>
> A. As explained in (2) and (4) above, there isn't a standard way for MDB applications to short-circuit the use of
> message destination references and define the JNDI name of the destination from which a JMS message-driven bean consumes
> messages, either using {{ejb-jar.xml}} or annotations. This contrasts with EJBs which send messages, where the JNDI name
> of the destination can be specified in the MDB code using the JNDI API or a {{_at_Resource(lookup="jms/foo")}} declaration.
>
> B. As explained in (3) above, there is no standard way for the application to define using annotation the "message
> destination reference" on which the JMS message-driven bean is consuming messages.
>
> h3. Proposals:
>
> A. *It is proposed* that the {{<message-driven>}} element in {{ejb-jar.xml}} be extended to define an additional
> sub-element which can be used to specify the JNDI name of the destination from which a JMS message-driven mean consumes
> messages. A suggested element name is {{<message-destination-jndi-name>}}:
>
> {noformat}
> <ejb-jar>
> <display-name>Ejb1</display-name>
> <enterprise-beans>
> <message-driven>
> <display-name>MDB1</display-name>
> <ejb-name>MessageBean</ejb-name>
> <message-destination-type>javax.jms.Queue</message-destination-type>
> <message-destination-jndi-name>jms/inboundQueue<message-destination-jndi-name>
> ...
>
> {noformat}
>
> It might be asked why this needs to be defined by a new subelement of {{<message-driven>}} rather than, say, a new
> standard activation configuration property. The answer is that the way that the JNDI name is defined needs to be
> consistent with the way that the message destination reference is defined, which is by the
> {{<message-destination-link>}} subelement of {{<message-driven>}}
>
> B. *It is proposed* that the equivalent annotation be a new attribute of the {{_at_MessageDriven}} annotation, called
> {{message-destination-jndi-name}}. For example:
>
> {noformat}
> MessageDriven(message-destination-jndi-name="jms/inboundQueue")
> public class MyMDB implements MessageListener {
> ....
> {noformat}
>
> C. *It is proposed* that the {{_at_MessageDriven}} annotation be extended to allow applications to define the "message
> destination reference" on which the JMS message-driven bean is consuming messages, using a new attribute
> {{message-destination-link"}}
>
> {noformat}
> MessageDriven(message-destination-link="ExpenseProcessingQueue")
> public class MyMDB implements MessageListener {
> ....
> {noformat}
>
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