Management

Apache ActiveMQ Artemis has an extensive management API that allows a user to modify a server configuration, create new resources (e.g. addresses and queues), inspect these resources (e.g. how many messages are currently held in a queue) and interact with it (e.g. to remove messages from a queue). Apache ActiveMQ Artemis also allows clients to subscribe to management notifications.

There are four ways to access Apache ActiveMQ Artemis management API:

• Using JMX -- JMX is the standard way to manage Java applications

• Using Jolokia -- Jolokia exposes the JMX API of an application through a REST interface

• Using the Core Client -- management operations are sent to Apache ActiveMQ Artemis server using Core Client messages

• Using the Core JMS Client -- management operations are sent to Apache ActiveMQ Artemis server using Core JMS Client messages

Although there are four different ways to manage Apache ActiveMQ Artemis, each API supports the same functionality. If it is possible to manage a resource using JMX it is also possible to achieve the same result using Core messages.

Besides the programmatic management interfaces, a Web Console and a Command Line management utility are also available to administrators of ActiveMQ Artemis.

The choice depends on your requirements, your application settings and your environment to decide which way suits you best.

Note

In version 2 of Apache ActiveMQ Artemis the syntax used for MBean Object names has changed significantly due to changes in the addressing scheme. See the documentation for each individual resource for details on the new syntax.

The Management API

Regardless of the way you invoke management operations, the management API is the same.

For each managed resource, there exists a Java interface describing what operations can be invoked for this type of resource.

To learn about available management operations, see the Javadoc for these interfaces. They are located in the org.apache.activemq.artemis.api.core.management package and they are named with the word Control at the end.

The way to invoke management operations depends on whether JMX, Core messages, or Core JMS messages are used.

Management API

For full details of the API please consult the Javadoc. In summary:

Server Management

The ActiveMQServerControl interface is the entry point for broker management.

• Listing, creating, deploying and destroying queues

  A list of deployed queues can be retrieved using the getQueueNames() method.

  Queues can be created or destroyed using the management operations createQueue() or deployQueue() or destroyQueue()

  createQueue will fail if the queue already exists while deployQueue will do nothing.

• Listing and closing remote connections

  Client's remote addresses can be retrieved using listRemoteAddresses(). It is also possible to close the connections associated with a remote address using the closeConnectionsForAddress() method.

  Alternatively, connection IDs can be listed using listConnectionIDs() and all the sessions for a given connection ID can be listed using listSessions().

• Transaction heuristic operations

  In case of a server crash, when the server restarts, it it possible that some transaction requires manual intervention. The listPreparedTransactions() method lists the transactions which are in the prepared states (the transactions are represented as opaque Base64 Strings.) To commit or rollback a given prepared transaction, the commitPreparedTransaction() or rollbackPreparedTransaction() method can be used to resolve heuristic transactions. Heuristically completed transactions can be listed using the listHeuristicCommittedTransactions() and listHeuristicRolledBackTransactions methods.

• Enabling and resetting Message counters

  Message counters can be enabled or disabled using the enableMessageCounters() or disableMessageCounters() method. To reset message counters, it is possible to invoke resetAllMessageCounters() and resetAllMessageCounterHistories() methods.

• Retrieving the server configuration and attributes

  The ActiveMQServerControl exposes Apache ActiveMQ Artemis server configuration through all its attributes (e.g. getVersion() method to retrieve the server's version, etc.)

• Listing, creating and destroying Core bridges and diverts

  A list of deployed core bridges (resp. diverts) can be retrieved using the getBridgeNames() (resp. getDivertNames()) method.

  Core bridges (resp. diverts) can be created or destroyed using the management operations createBridge() and destroyBridge() (resp. createDivert() and destroyDivert()).

• It is possible to stop the server and force failover to occur with any currently attached clients.

  To do this use the forceFailover() operation.

  Note

  Since this method actually stops the server you will probably receive some sort of error depending on which management service you use to call it.

Address Management

Individual addresses can be managed using the AddressControl interface.

• Modifying roles and permissions for an address

  You can add or remove roles associated to a queue using the addRole() or removeRole() methods. You can list all the roles associated to the queue with the getRoles() method

Queue Management

The bulk of the management API deals with queues. The QueueControl interface defines the queue management operations.

Most of the management operations on queues take either a single message ID (e.g. to remove a single message) or a filter (e.g. to expire all messages with a given property.)

Note

Passing null or an empty string in the filter parameter means that the management operation will be performed on all messages in a queue.

• Expiring, sending to a dead letter address and moving messages

  Messages can be expired from a queue by using the expireMessages() method. If an expiry address is defined, messages will be sent to it, otherwise they are discarded. The queue's expiry address can be set with the setExpiryAddress() method.

  Messages can also be sent to a dead letter address with the sendMessagesToDeadLetterAddress() method. It returns the number of messages which are sent to the dead letter address. If a dead letter address is not defined, message are removed from the queue and discarded. The queue's dead letter address can be set with the setDeadLetterAddress() method.

  Messages can also be moved from a queue to another queue by using the moveMessages() method.

• Listing and removing messages

  Messages can be listed from a queue by using the listMessages() method which returns an array of Map, one Map for each message.

  Messages can also be removed from the queue by using the removeMessages() method which returns a boolean for the single message ID variant or the number of removed messages for the filter variant. The removeMessages() method takes a filter argument to remove only filtered messages. Setting the filter to an empty string will in effect remove all messages.

• Counting messages

  The number of messages in a queue is returned by the getMessageCount() method. Alternatively, the countMessages() will return the number of messages in the queue which match a given filter.

• Changing message priority

  The message priority can be changed by using the changeMessagesPriority() method which returns a boolean for the single message ID variant or the number of updated messages for the filter variant.

• Message counters

  Message counters can be listed for a queue with the listMessageCounter() and listMessageCounterHistory() methods (see Message Counters section). The message counters can also be reset for a single queue using the resetMessageCounter() method.

• Retrieving the queue attributes

  The QueueControl exposes queue settings through its attributes (e.g. getFilter() to retrieve the queue's filter if it was created with one, isDurable() to know whether the queue is durable or not, etc.)

• Pausing and resuming Queues

  The QueueControl can pause and resume the underlying queue. When a queue is paused, it will receive messages but will not deliver them. When it's resumed, it'll begin delivering the queued messages, if any.

Other Resources Management

Apache ActiveMQ Artemis allows to start and stop its remote resources (acceptors, diverts, bridges, etc.) so that a server can be taken off line for a given period of time without stopping it completely (e.g. if other management operations must be performed such as resolving heuristic transactions). These resources are:

• Acceptors

  They can be started or stopped using the start() or. stop() method on the AcceptorControl interface. The acceptors parameters can be retrieved using the AcceptorControl attributes (see Understanding Acceptors)

• Diverts

  They can be started or stopped using the start() or stop() method on the DivertControl interface. Diverts parameters can be retrieved using the DivertControl attributes (see Diverting and Splitting Message Flows))

• Bridges

  They can be started or stopped using the start() (resp. stop()) method on the BridgeControl interface. Bridges parameters can be retrieved using the BridgeControl attributes (see Core bridges)

• Broadcast groups

  They can be started or stopped using the start() or stop() method on the BroadcastGroupControl interface. Broadcast groups parameters can be retrieved using the BroadcastGroupControl attributes (see Clusters)

• Cluster connections

  They can be started or stopped using the start() or stop() method on the ClusterConnectionControl interface. Cluster connections parameters can be retrieved using the ClusterConnectionControl attributes (see Clusters)

Using Management Via JMX

Apache ActiveMQ Artemis can be managed using JMX.

The management API is exposed by Apache ActiveMQ Artemis using MBeans interfaces. Apache ActiveMQ Artemis registers its resources with the domain org.apache.activemq.artemis.

For example, the ObjectName to manage the anycast queue exampleQueue on the address exampleAddress is:

org.apache.activemq.artemis:broker=<brokerName>,component=addresses,address="exampleAddress",subcomponent=queues,routing-type="anycast",queue="exampleQueue"

and the MBean is:

org.apache.activemq.artemis.api.core.management.QueueControl

The MBean ObjectName's are built using the helper class org.apache.activemq.artemis.api.core.management.ObjectNameBuilder. You can also use jconsole to find the ObjectName of the MBean you want to manage.

Example usage of the ObjectNameBuilder to obtain ActiveMQServerControl's name:

brokerName = "0.0.0.0";  // configured e.g. in broker.xml <broker-name> element
objectNameBuilder = ObjectNameBuilder.create(ArtemisResolver.DEFAULT_DOMAIN, brokerName, true);
serverObjectName = objectNameBuilder.getActiveMQServerObjectName()

Managing Apache ActiveMQ Artemis using JMX is identical to management of any Java Applications using JMX. It can be done by reflection or by creating proxies of the MBeans.

Configuring JMX

By default, JMX is enabled to manage Apache ActiveMQ Artemis. It can be disabled by setting jmx-management-enabled to false in broker.xml:

<!-- false to disable JMX management for Apache ActiveMQ Artemis -->
<jmx-management-enabled>false</jmx-management-enabled>

Role Based Authorisation for JMX

Although by default Artemis uses the Java Virtual Machine's Platform MBeanServer this is guarded using role based authentication that leverages Artemis's JAAS plugin support. This is configured via the authorisation element in the management.xml configuration file and can be used to restrict access to attributes and methods on mbeans.

There are 3 elements within the authorisation element, whitelist, default-access and role-access, Lets discuss each in turn.

Whitelist contains a list of mBeans that will by pass the authentication, this is typically used for any mbeans that are needed by the console to run etc. The default configuration is:

<whitelist>
   <entry domain="hawtio"/>
</whitelist>

This means that any mbean with the domain hawtio will be allowed access without authorisation. for instance hawtio:plugin=artemis. You can also use wildcards for the mBean properties so the following would also match.

<whitelist>
   <entry domain="hawtio" key="type=*"/>
</whitelist>

The role-accessdefines how roles are mapped to particular mBeans and its attributes and methods, the default configuration looks like:

<role-access>
    <match domain="org.apache.activemq.artemis">
       <access method="list*" roles="view,update,amq"/>
       <access method="get*" roles="view,update,amq"/>
       <access method="is*" roles="view,update,amq"/>
       <access method="set*" roles="update,amq"/>
       <access method="*" roles="amq"/>
    </match>
</role-access>

This contains 1 match and will be applied to any mBean that has the domain org.apache.activemq.artemis. Any access to any mBeans that have this domain are controlled by the access elements which contain a method and a set of roles. The method being invoked will be used to pick the closest matching method and the roles for this will be applied for access. For instance if you try the invoke a method called listMessages on an mBean with the org.apache.activemq.artemis domain then this would match the access with the method of list*. You could also explicitly configure this by using the full method name, like so:

<access method="listMessages" roles="view,update,amq"/>

You can also match specific mBeans within a domain by adding a key attribute that is used to match one of the properties on the mBean, like:

<match domain="org.apache.activemq.artemis" key="subcomponent=queues">
   <access method="list*" roles="view,update,amq"/>
   <access method="get*" roles="view,update,amq"/>
   <access method="is*" roles="view,update,amq"/>
   <access method="set*" roles="update,amq"/>
   <access method="*" roles="amq"/>
</match>

You could also match a specific queue for instance :

org.apache.activemq.artemis:broker=<brokerName>,component=addresses,address="exampleAddress",subcomponent=queues,routing-type="anycast",queue="exampleQueue"

by configuring:

<match domain="org.apache.activemq.artemis" key="queue=exampleQueue">
   <access method="list*" roles="view,update,amq"/>
   <access method="get*" roles="view,update,amq"/>
   <access method="is*" roles="view,update,amq"/>
   <access method="set*" roles="update,amq"/>
   <access method="*" roles="amq"/>
</match>

Access to JMX mBean attributes are converted to method calls so these are controlled via the set*, get* and is*. The * access is the catch all for everything other method that isn't specifically matched.

The default-access element is basically the catch all for every method call that isn't handled via the role-access configuration. This has teh same semantics as a match element.

Note

If JMX is enabled, Apache ActiveMQ Artemis can not be managed locally using jconsole when connecting as a local process, this is because jconsole does not using any authentication when connecting this way. If you want to use jconsole you will either have to disable authentication, by removing the authentication element or enable remote access.

Configuring remote JMX Access

By default remote JMX access to Artemis is disabled for security reasons.

Artemis has a JMX agent which allows access to JMX mBeans remotely. This is configured via the connector element in the management.xml configuration file. To enable this you simply add the following xml:

<connector connector-port="1099"/>

This exposes the agent remotely on the port 1099. If you were connecting via jconsole you would connect as a remote process using the service url service:jmx:rmi:///jndi/rmi://localhost:1099/jmxrmi and an appropriate user name and password.

You can also configure the connector using the following:

• connector-host

  The host to expose the agent on

• connector-port

  The port to expose the agent on

• jmx-realm

  The jmx realm to use for authentication, defaults to activemq to match the JAAS configuration.

• object-name

  The object name to expose the remote connector on, default is connector:name=rmi

• secured

  Whether the connector is secured using SSL

• key-store-path

  The location of the keystore

• key-store-password

  The keystore password

• key-store-provider The provider, JKS by default

• trust-store-path

  The location of the truststore

• trust-store-password

  The trustore password

• trust-store-provider

  The provider, JKS by default

Note

It is important to note that the rmi registry will pick an ip address to bind to, If you have a multi IP addresses/NICs
present on the system then you can choose the ip address to use by adding the following to artemis.profile -Djava.rmi.server.hostname=localhost

Note

Remote connections using the default JVM Agent not enabled by default as Artemis exposes the mBean Server via its own configuration. This is so Artemis can leverage the JAAS authentication layer via JMX. If you want to expose this then you will need to disable both the connector and the authorisation by removing them from the management.xml configuration. Please refer to Java Management guide to configure the server for remote management (system properties must be set in artemis.profile).

By default, Apache ActiveMQ Artemis server uses the JMX domain "org.apache.activemq.artemis". To manage several Apache ActiveMQ Artemis servers from the same MBeanServer, the JMX domain can be configured for each individual Apache ActiveMQ Artemis server by setting jmx-domain in broker.xml:

<!-- use a specific JMX domain for ActiveMQ Artemis MBeans -->
<jmx-domain>my.org.apache.activemq</jmx-domain>

Example

See the Examples chapter for an example which shows how to use a remote connection to JMX and MBean proxies to manage Apache ActiveMQ Artemis.

Exposing JMX using Jolokia

The default Broker configuration ships with the Jolokia HTTP agent deployed as a Web Application. Jolokia is a remote JMX-over-HTTP bridge that exposes MBeans. For a full guide as to how to use it refer to Jolokia Documentation, however a simple example to query the broker's version would be to use a browser and go to the URL http://username:password@localhost:8161/console/jolokia/read/org.apache.activemq.artemis:broker="0.0.0.0"/Version.

This would give you back something like the following:

{"request":{"mbean":"org.apache.activemq.artemis:broker=\"0.0.0.0\"","attribute":"Version","type":"read"},"value":"2.0.0-SNAPSHOT","timestamp":1487017918,"status":200}

JMX and the Console

The console that ships with Artemis uses Jolokia under the covers which in turn uses JMX. This will use the authentication configuration in the management.xml file as described in the previous section. This means that when mBeans are accessed via the console the credentials used to log into the console and the roles associated with them. By default access to the console is only allow via users with the amq role. This is configured in the artemis.profile via the system property -Dhawtio.role=amq. You can configure multiple roles by changing this to -Dhawtio.roles=amq,view,update.

If a user doesn't have the correct role to invoke a specific operation then this will display an authorisation exception in the console.

Using Management Message API

The management message API in ActiveMQ Artemis is accessed by sending Core Client messages to a special address, the management address.

Management messages are regular Core Client messages with well-known properties that the server needs to understand to interact with the management API:

• The name of the managed resource

• The name of the management operation

• The parameters of the management operation

When such a management message is sent to the management address, Apache ActiveMQ Artemis server will handle it, extract the information, invoke the operation on the managed resources and send a management reply to the management message's reply-to address (specified by ClientMessageImpl.REPLYTO_HEADER_NAME).

A ClientConsumer can be used to consume the management reply and retrieve the result of the operation (if any) stored in the reply's body. For portability, results are returned as a JSON String rather than Java Serialization (the org.apache.activemq.artemis.api.core.management.ManagementHelper can be used to convert the JSON string to Java objects).

These steps can be simplified to make it easier to invoke management operations using Core messages:

1. Create a ClientRequestor to send messages to the management address and receive replies

2. Create a ClientMessage

3. Use the helper class org.apache.activemq.artemis.api.core.management.ManagementHelper to fill the message with the management properties

4. Send the message using the ClientRequestor

5. Use the helper class org.apache.activemq.artemis.api.core.management.ManagementHelper to retrieve the operation result from the management reply

For example, to find out the number of messages in the queue exampleQueue:

ClientSession session = ...
ClientRequestor requestor = new ClientRequestor(session, "activemq.management");
ClientMessage message = session.createMessage(false);
ManagementHelper.putAttribute(message, "queue.exampleQueue", "messageCount");
session.start();
ClientMessage reply = requestor.request(m);
int count = (Integer) ManagementHelper.getResult(reply);
System.out.println("There are " + count + " messages in exampleQueue");

Management operation name and parameters must conform to the Java interfaces defined in the management packages.

Names of the resources are built using the helper class org.apache.activemq.artemis.api.core.management.ResourceNames and are straightforward (e.g. queue.exampleQueue for QueueControl of the Queue exampleQueue, or broker for the ActiveMQServerControl).

NOTE

The ManagementHelper class can be used only with Core JMS messages. When called with a message from a different JMS library, an exception will be thrown.

Configuring Management

The management address to send management messages is configured in broker.xml:

<management-address>activemq.management</management-address>

By default, the address is activemq.management.

The management address requires a special user permission manage to be able to receive and handle management messages. This is also configured in broker.xml:

<!-- users with the admin role will be allowed to manage -->
<!-- Apache ActiveMQ Artemis using management messages        -->
<security-setting match="activemq.management">
   <permission type="manage" roles="admin" />
</security-setting>

Example

See the Examples chapter for an example which shows how to use JMS messages to manage the Apache ActiveMQ Artemis server.

Management Notifications

Apache ActiveMQ Artemis emits notifications to inform listeners of potentially interesting events (creation of new resources, security violation, etc.).

These notifications can be received by two different ways:

• JMX notifications

• Notification messages

JMX Notifications

If JMX is enabled (see Configuring JMX section), JMX notifications can be received by subscribing to org.apache.activemq.artemis:type=Broker,brokerName=<broker name>,module=Core,serviceType=Server for notifications on resources.

Notification Messages

Apache ActiveMQ Artemis defines a special management notification address. Queues can be bound to this address so that clients will receive management notifications as messages.

A client which wants to receive management notifications must create a queue bound to the management notification address. It can then receive the notifications from its queue.

Notifications messages are regular messages with additional properties corresponding to the notification (its type, when it occurred, the resources which were concerned, etc.).

Since notifications are regular messages, it is possible to use message selectors to filter out notifications and receives only a subset of all the notifications emitted by the server.

Configuring The Management Notification Address

The management notification address to receive management notifications is configured in broker.xml:

<management-notification-address>activemq.notifications</management-notification-address>

By default, the address is activemq.notifications.

Receiving Notification Messages

Apache ActiveMQ Artemis's Core JMS Client can be used to receive notifications:

Topic notificationsTopic = ActiveMQJMSClient.createTopic("activemq.notifications");

Session session = ...
MessageConsumer notificationConsumer = session.createConsumer(notificationsTopic);
notificationConsumer.setMessageListener(new MessageListener()
{
   public void onMessage(Message notif)
   {
      System.out.println("------------------------");
      System.out.println("Received notification:");
      try
      {
         Enumeration propertyNames = notif.getPropertyNames();
         while (propertyNames.hasMoreElements())
         {
            String propertyName = (String)propertyNames.nextElement();
            System.out.format("  %s: %s\n", propertyName, notif.getObjectProperty(propertyName));
         }
      }
      catch (JMSException e)
      {
      }
      System.out.println("------------------------");
   }
});

Example

See the Examples chapter for an example which shows how to use a JMS MessageListener to receive management notifications from ActiveMQ Artemis server.

Notification Types and Headers

Below is a list of all the different kinds of notifications as well as which headers are on the messages. Every notification has a _AMQ_NotifType (value noted in parentheses) and _AMQ_NotifTimestamp header. The timestamp is the un-formatted result of a call to java.lang.System.currentTimeMillis().

• BINDING_ADDED (0)

  _AMQ_Binding_Type, _AMQ_Address, _AMQ_ClusterName, _AMQ_RoutingName, _AMQ_Binding_ID, _AMQ_Distance, _AMQ_FilterString

• BINDING_REMOVED (1)

  _AMQ_Address, _AMQ_ClusterName, _AMQ_RoutingName, _AMQ_Binding_ID, _AMQ_Distance, _AMQ_FilterString

• CONSUMER_CREATED (2)

  _AMQ_Address, _AMQ_ClusterName, _AMQ_RoutingName, _AMQ_Distance, _AMQ_ConsumerCount, _AMQ_User, _AMQ_RemoteAddress, _AMQ_SessionName, _AMQ_FilterString

• CONSUMER_CLOSED (3)

  _AMQ_Address, _AMQ_ClusterName, _AMQ_RoutingName, _AMQ_Distance, _AMQ_ConsumerCount, _AMQ_User, _AMQ_RemoteAddress, _AMQ_SessionName, _AMQ_FilterString

• SECURITY_AUTHENTICATION_VIOLATION (6)

  _AMQ_User

• SECURITY_PERMISSION_VIOLATION (7)

  _AMQ_Address, _AMQ_CheckType, _AMQ_User

• DISCOVERY_GROUP_STARTED (8)

  name

• DISCOVERY_GROUP_STOPPED (9)

  name

• BROADCAST_GROUP_STARTED (10)

  name

• BROADCAST_GROUP_STOPPED (11)

  name

• BRIDGE_STARTED (12)

  name

• BRIDGE_STOPPED (13)

  name

• CLUSTER_CONNECTION_STARTED (14)

  name

• CLUSTER_CONNECTION_STOPPED (15)

  name

• ACCEPTOR_STARTED (16)

  factory, id

• ACCEPTOR_STOPPED (17)

  factory, id

• PROPOSAL (18)

  _JBM_ProposalGroupId, _JBM_ProposalValue, _AMQ_Binding_Type, _AMQ_Address, _AMQ_Distance

• PROPOSAL_RESPONSE (19)

  _JBM_ProposalGroupId, _JBM_ProposalValue, _JBM_ProposalAltValue, _AMQ_Binding_Type, _AMQ_Address, _AMQ_Distance

• CONSUMER_SLOW (21)

  _AMQ_Address, _AMQ_ConsumerCount, _AMQ_RemoteAddress, _AMQ_ConnectionName, _AMQ_ConsumerName, _AMQ_SessionName

Message Counters

Message counters can be used to obtain information on queues over time as Apache ActiveMQ Artemis keeps a history on queue metrics.

They can be used to show trends on queues. For example, using the management API, it would be possible to query the number of messages in a queue at regular interval. However, this would not be enough to know if the queue is used: the number of messages can remain constant because nobody is sending or receiving messages from the queue or because there are as many messages sent to the queue than messages consumed from it. The number of messages in the queue remains the same in both cases but its use is widely different.

Message counters give additional information about the queues:

• count

  The total number of messages added to the queue since the server was started

• countDelta

  the number of messages added to the queue since the last message counter update

• messageCount

  The current number of messages in the queue

• messageCountDelta

  The overall number of messages added/removed from the queue since the last message counter update. For example, if messageCountDelta is equal to -10 this means that overall 10 messages have been removed from the queue (e.g. 2 messages were added and 12 were removed)

• lastAddTimestamp

  The timestamp of the last time a message was added to the queue

• udpateTimestamp

  The timestamp of the last message counter update

These attributes can be used to determine other meaningful data as well. For example, to know specifically how many messages were consumed from the queue since the last update simply subtract the messageCountDelta from countDelta.

Configuring Message Counters

By default, message counters are disabled as it might have a small negative effect on memory.

To enable message counters, you can set it to true in broker.xml:

<message-counter-enabled>true</message-counter-enabled>

Message counters keep a history of the queue metrics (10 days by default) and sample all the queues at regular interval (10 seconds by default). If message counters are enabled, these values should be configured to suit your messaging use case in broker.xml:

<!-- keep history for a week -->
<message-counter-max-day-history>7</message-counter-max-day-history>
<!-- sample the queues every minute (60000ms) -->
<message-counter-sample-period>60000</message-counter-sample-period>

Message counters can be retrieved using the Management API. For example, to retrieve message counters on a queue using JMX:

// retrieve a connection to Apache ActiveMQ Artemis's MBeanServer
MBeanServerConnection mbsc = ...
QueueControlMBean queueControl = (QueueControl)MBeanServerInvocationHandler.newProxyInstance(mbsc,
   on,
   QueueControl.class,
   false);
// message counters are retrieved as a JSON String
String counters = queueControl.listMessageCounter();
// use the MessageCounterInfo helper class to manipulate message counters more easily
MessageCounterInfo messageCounter = MessageCounterInfo.fromJSON(counters);
System.out.format("%s message(s) in the queue (since last sample: %s)\n",
messageCounter.getMessageCount(),
messageCounter.getMessageCountDelta());

Example

See the Examples chapter for an example which shows how to use message counters to retrieve information on a queue.