[[Message_Driven_Beans_Controlled_Delivery]]
= Message Driven Beans Controlled Delivery

There are three mechanisms in WildFly that allow controlling if a
specific MDB is actively receiving or not messages:

* delivery active
* delivery groups
* clustered singleton

We will see each one of them in the following sections.

[[delivery-active]]
== Delivery Active

Delivery active is simply an attribute associated with the MDB that
indicates if the MDB is receiving messages or not. If an MDB is not
currently receiving messages, the messages will be saved in the queue or
topic for later, according to the rules of the topic/queue.

You can configure delivery active using xml or annotations, and you can
change its value after deployment using the cli.

* jboss-ejb3.xml:

In the jboss-ejb3 xml file, configure the value of active as false to
mark that the MDB will not be receiving messages as soon as it is
deployed:

[source,xml,options="nowrap"]
----
<?xml version="1.1" encoding="UTF-8"?>
<jboss:ejb-jar xmlns:jboss="http://www.jboss.com/xml/ns/javaee"
               xmlns="http://java.sun.com/xml/ns/javaee"
               xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
               xmlns:d="urn:delivery-active:1.2"
               xsi:schemaLocation="http://www.jboss.com/xml/ns/javaee http://www.jboss.org/j2ee/schema/jboss-ejb3-2_0.xsd http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/ejb-jar_3_1.xsd"                version="3.1"
               impl-version="2.0">
    <assembly-descriptor>
        <d:delivery>
            <ejb-name>HelloWorldQueueMDB</ejb-name>
            <d:active>false</d:active>
        </d:delivery>
    </assembly-descriptor>
</jboss:ejb-jar>
----

You can use a wildcard "*" in the place of ejb-name if you want to apply
that active value to all MDBs in your application.

* annotation

Alternatively, you can use the org.jboss.ejb3.annotation.DeliveryActive
annotation, as in the example below:

[source,java,options="nowrap"]
----
@MessageDriven(name = "HelloWorldMDB", activationConfig = {

 @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue"),

 @ActivationConfigProperty(propertyName = "destination", propertyValue = "queue/HELLOWORLDMDBQueue"),

 @ActivationConfigProperty(propertyName = "acknowledgeMode", propertyValue = "Auto-acknowledge") })

@DeliveryActive(false)

public class HelloWorldMDB implements MessageListener {
    public void onMessage(Message rcvMessage) {
      // ...
    }
}
----

[[start-delivery-and-stop-delivery]]
=== Start-delivery and Stop-Delivery

These management operations dynamically change the value of the active
attribute, enabling or disabling delivery for the MDB. at runtime To use
them, connect to the WildFly instance you want to manage, then enter the
path of the MDB you want to manage delivery for:

[source,options="nowrap"]
----
[standalone@localhost:9990 /] cd deployment=jboss-helloworld-mdb.war/subsystem=ejb3/message-driven-bean=HelloWorldMDB

[standalone@localhost:9990 message-driven-bean=HelloWorldMDB] :stop-delivery
{"outcome" => "success"}

[standalone@localhost:9990 message-driven-bean=HelloWorldMDB] :start-delivery
{"outcome" => "success"}
----

[[delivery-groups]]
== Delivery Groups

Delivery groups provide a straightforward way to manage delivery for a
group of MDBs. Every MDB belonging to a delivery group has delivery
active if that group is active, and has delivery inactive
whenever the group is not active.

You can add a delivery group to the ejb3 subsystem using either the
subsystem xml or cli. Next, we will see examples of each case. In those
examples we will add only a single delivery group, but keep in mind that
you can add as many delivery groups as you need to a WildFly instance.

* the ejb3 subsystem xml (located in your configuration xml, such as
standalone.xml)

[source,xml,options="nowrap"]
----
<subsystem xmlns="urn:jboss:domain:ejb3:4.0">
    ...
    <mdb>
        ...
        <delivery-groups>
            <delivery-group name="mdb-group-name" active="true"/>
        </delivery-groups>
    </mdb>
    ...
</subsystem>
----

The example above adds a delivery group named "mdb-group-name" (you can
use whatever name suits you best as the group name). The "true" active
attribute indicates that all MDBs belonging to that group will have
delivery active right after deployment. If you mark that attribute as
false, you are indicating that every MDB belonging to the group will not
start receiving messages after deployment, a condition that will remain
until the group becomes active.

* jboss-cli

You can add a mdb-delivery-group using the add command as below:

[source,options="nowrap"]
----
[standalone@localhost:9990 /] ./subsystem=ejb3/mdb-delivery-group=mdb-group-name:add
{"outcome" => "success"}
----

[[reading-and-writing-the-delivery-state-of-a-delivery-group]]
=== Reading and Writing the Delivery State of a Delivery Group

You can check whether delivery is active for a group by reading the
active attribute, which defaults to true:

[source,options="nowrap"]
----
[standalone@localhost:9990 /] ./subsystem=ejb3/mdb-delivery-group=mdb-group-name:read-attribute(name=active)
{ "outcome" => "success", "result" => true }
----

To make the the delivery-group inactive, just write the active attribute
with a false value:

[source,options="nowrap"]
----
[standalone@localhost:9990 /] ./subsystem=ejb3/mdb-delivery-group=mdb-group-name:write-attribute(name=active,value=false)
{"outcome" => "success"}

[standalone@localhost:9990 /] ./subsystem=ejb3/mdb-delivery-group=mdb-group-name:read-attribute(name=active)
{ "outcome" => "success", "result" => false }
----

To make it active again, write the attribute with a true value:

[source,options="nowrap"]
----
[standalone@localhost:9990 /] ./subsystem=ejb3/mdb-delivery-group=mdb-group-name:write-attribute(name=active,value=true)
{"outcome" => "success"}

[standalone@localhost:9990 /] ./subsystem=ejb3/mdb-delivery-group=mdb-group-name:read-attribute(name=active)
{ "outcome" => "success", "result" => true }
----

[[using-delivery-groups]]
=== Using Delivery Groups

To mark that an MDB belongs to a delivery-group, declare so in the
jboss-ejb3.xml file:

[source,xml,options="nowrap"]
----
<?xml version="1.1" encoding="UTF-8"?>

<jboss:ejb-jar xmlns:jboss="http://www.jboss.com/xml/ns/javaee"
               xmlns="http://java.sun.com/xml/ns/javaee"
               xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
               xmlns:d="urn:delivery-active:1.2"
               xsi:schemaLocation="http://www.jboss.com/xml/ns/javaee http://www.jboss.org/j2ee/schema/jboss-ejb3-2_0.xsd http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/ejb-jar_3_1.xsd"
               version="3.1"
               impl-version="2.0">
    <assembly-descriptor>
        <d:delivery>
            <ejb-name>HelloWorldMDB</ejb-name>
            <d:group>mdb-delivery-group</d:group>
        </d:delivery>
    </assembly-descriptor>
</jboss:ejb-jar>
----

You can also use a wildcard to mark that all MDBs in your application
belong to a delivery-group. In the following example, we add all MDBs in
the application to group1, except for HelloWorldMDB, that is added to
group2:

[source,xml,options="nowrap"]
----
<?xml version="1.1" encoding="UTF-8"?>
<jboss:ejb-jar xmlns:jboss="http://www.jboss.com/xml/ns/javaee"
               xmlns="http://java.sun.com/xml/ns/javaee"
               xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
               xmlns:d="urn:delivery-active:1.2"
               xsi:schemaLocation="http://www.jboss.com/xml/ns/javaee http://www.jboss.org/j2ee/schema/jboss-ejb3-2_0.xsd http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/ejb-jar_3_1.xsd"
               version="3.1"
               impl-version="2.0">
    <assembly-descriptor>
        <d:delivery>
            <ejb-name>*</ejb-name>
            <d:group>group1</d:group>
        </d:delivery>
        <d:delivery>
            <ejb-name>HelloWorldMDB</ejb-name>
            <d:group>group2</d:group>
        </d:delivery>
    </assembly-descriptor>
</jboss:ejb-jar>
----

Another option is to use org.jboss.ejb3.annotation.DeliveryGroup
annotation on each MDB class belonging to a group:

[source,java,options="nowrap"]
----
@MessageDriven(name = "HelloWorldQueueMDB", activationConfig = {
 @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue"),
 @ActivationConfigProperty(propertyName = "destination", propertyValue = "queue/HELLOWORLDMDBQueue"),
 @ActivationConfigProperty(propertyName = "acknowledgeMode", propertyValue = "Auto-acknowledge") })

@DeliveryGroup("group2")

public class HelloWorldMDB implements MessageListener {
    ...
}
----

A MDB can belong to more than one delivery group. See the following example:
[source,xml]
----
<?xml version="1.1" encoding="UTF-8"?>

<jboss:ejb-jar xmlns:jboss="http://www.jboss.com/xml/ns/javaee"
               xmlns="http://java.sun.com/xml/ns/javaee"
               xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
               xmlns:d="urn:delivery-active:1.2"
               xsi:schemaLocation="http://www.jboss.com/xml/ns/javaee http://www.jboss.org/j2ee/schema/jboss-ejb3-2_0.xsd http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/ejb-jar_3_1.xsd"
               version="3.1"
               impl-version="2.0">
    <assembly-descriptor>
        <d:delivery>
            <ejb-name>*</ejb-name>
            <d:group>mdb-delivery-group1</d:group>
        </d:delivery>
        <d:delivery>
            <ejb-name>HelloWorldMDB</ejb-name>
            <d:group>mdb-delivery-group2</d:group>
            <d:group>mdb-delivery-group3</d:group>
        </d:delivery>
    </assembly-descriptor>
</jboss:ejb-jar>
----

In the example above, we use the wildcard to specify that every MDB in the
ejb-jar will belong to mdb-delivery-group1.
That means that, in order for delivery of messages to be active for those MDBs,
mdb-delivery-group1 must be active.

In addition, the configuration above specifies that HelloWorldMDB belongs also
to mdb-delivery-group2 and mdb-delivery-group3. So, delivery of messages to
 HelloWorldMDB will only be active when mdb-delivery-group1,
 mdb-delivery-group2, and mdb-delivery-group3 are all active.

The same could be specified using the @DeliveryGroup annotation:

[source, java]
----
@MessageDriven(name = "HelloWorldQueueMDB", activationConfig = {
 @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue"),
 @ActivationConfigProperty(propertyName = "destination", propertyValue = "queue/HELLOWORLDMDBQueue"),
 @ActivationConfigProperty(propertyName = "acknowledgeMode", propertyValue = "Auto-acknowledge") })

@DeliveryGroup("mdb-delivery-group2")
@DeliveryGroup("mdb-delivery-group3")

public class HelloWorldMDB implements MessageListener {
    ...
}
----

Notice that all the delivery-groups used by an application must be installed in
the WildFly server upon deployment, or the deployment will fail with a message
stating that the delivery-group is missing.

[[clustered-singleton-delivery]]
== Clustered Singleton Delivery

Delivery can be marked as singleton in a clustered environment. In this
case, only one node in the cluster will have delivery active for that
MDB, whereas in all other nodes, delivery will be inactive. This option
can be used for applications that are deployed in all nodes of the
cluster. Such applications will be active in all nodes of the cluster,
except for the MDBs that are marked as clustered singleton. For those
MDBs, only one cluster node will be processing their messages. In case
that node stops, another node will have delivery activated, guaranteeing
that there is always one node processing the messages. This node is what
we call primary singleton provider of the MDB.

Notice that applications using clustered singleton delivery can only be
deployed in clustered WildFly servers (i.e., servers that are using the
ha configuration).

To mark delivery as clustered singleton, you can use the jboss-ejb3.xml
or the @ClusteredSingleton annotation:

* jboss-ejb3.xml:

[source,xml,options="nowrap"]
----
<?xml version="1.1" encoding="UTF-8"?>
<jboss:ejb-jar xmlns:jboss="http://www.jboss.com/xml/ns/javaee"
               xmlns="http://java.sun.com/xml/ns/javaee"
               xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
               xmlns:c="urn:clustering:1.1"
               xsi:schemaLocation="http://www.jboss.com/xml/ns/javaee http://www.jboss.org/j2ee/schema/jboss-ejb3-2_0.xsd http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/ejb-jar_3_1.xsd"
               version="3.1"
               impl-version="2.0">
    <assembly-descriptor>
        <c:clustering>
            <ejb-name>HelloWorldMDB</ejb-name>
            <c:clustered-singleton>true</c:clustered-singleton>
        </c:clustering>
    </assembly-descriptor>
</jboss:ejb-jar>
----

As in the previous jboss-ejb3.xml examples, a wildcard can be used in
the place of the ejb-name to indicate that all MDBs in the application
are singleton clustered.

* annotation

You can use the org.jboss.ejb3.annotation.ClusteredSingleton annotation
to mark an MDB as clustered singleton:

[source,java,options="nowrap"]
----
@MessageDriven(name = "HelloWorldQueueMDB", activationConfig = {
 @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue"),
 @ActivationConfigProperty(propertyName = "destination", propertyValue = "queue/HELLOWORLDMDBQueue"),
 @ActivationConfigProperty(propertyName = "acknowledgeMode", propertyValue = "Auto-acknowledge") })

@ClusteredSingleton

public class HelloWorldMDB implements MessageListener { ... }
----

[[using-multiple-mdb-delivery-control-mechanisms]]
== Using Multiple MDB Delivery Control Mechanisms

The previous delivery control mechanisms can be used together in a
single MDB. In this case, they work as a set of restrictions for
delivery to be active in a MDB.

For example, if an MDB belongs to one or more delivery groups and is also a
clustered singleton MDB, the delivery will be active for that MDB only
if the delivery groups are active in the cluster node that was elected as
the primary singleton provider.

Also, if you use jboss-cli to stopDelivery on a MDB that belongs to one or more
delivery groups, the MDB will stop receiving messages in case all groups
were active. If one or more of the groups associated with the MDB was not active,
the MDB will continue in the same, inactive state. But, once all groups become active,
the MDB will still be prevented from receiving messages, unless a startDelivery
operation is executed to revert the previously executed stopDelivery operation.

Invoking stopDelivery on an MDB that is marked as clustered singleton
will work in a similar way: no visible effect if the current node is not
the primary singleton provider; but it will stop delivery of messages
for that MDB if the current node is the primary singleton provider. If
the current node is not the primary singleton provider, but eventually becomes so, the
delivery of messages will not be active for that MDB, unless a
startDelivery operation is invoked.

In other words, when more than one delivery control mechanism is used in
conjunction, they act as a set of restrictions that need all to be true
in order for the MDB to receive messages:

* * MDB belongs to one delivery-group + stop-delivery was invoked*: the delivery group
needs to be active and the delivery needs to be restarted (via start-delivery) in order
for that MDB to start receiving messages;

* * MDB belongs to one delivery-group + MDB is clustered singleton*: the delivery group
needs to be active and the current node needs to be the primary singleton provider
node in order for that MDB to start receiving messages;

* * MDB belongs to one delivery-group + MDB is clustered singleton + stop-delivery was invoked*:
as above, the delivery-group has to be active, the current cluster node must be the
primary singleton provider node, plus, start-delivery needs to be invoked on that MDB,
only with these three factors being true the MDB will start receiving messages.

* * MDB belongs to multiple delivery-groups + stop-delivery was invoked*: all the delivery
groups need to be active and the delivery needs to be restarted (via start-delivery) in
order for that MDB to start receiving messages;

* * MDB belongs to multiple delivery-groups + MDB is clustered singleton*: all the delivery
groups need to be active and the current node needs to be the primary singleton
provider node in order for that MDB to start receiving messages;

* * MDB belongs to multiple delivery-groups + MDB is clustered singleton + stop-delivery was
invoked*: as above, all delivery-groups must be active, and current cluster node has to be the
primary singleton provider node, plus, start-delivery needs to be invoked on that MDB, only
with these three factors being true the MDB will start receiving messages.
