29. JMX Support

Spring Integration provides Channel Adapters for receiving and publishing JMX Notifications. There is also an inbound Channel Adapter for polling JMX MBean attribute values, and an outbound Channel Adapter for invoking JMX MBean operations.

29.1 Notification Listening Channel Adapter

The Notification-listening Channel Adapter requires a JMX ObjectName for the MBean that publishes Notifications to which this listener should be registered. A very simple configuration might look like this:

 <jmx:notification-listening-channel-adapter id="adapter"

The notification-listening-channel-adapter registers with an MBeanServer at startup, and the default bean name is "mbeanServer" which happens to be the same bean name generated when using Spring's <context:mbean-server/> element. If you need to use a different name be sure to include the "mbean-server" attribute.

The adapter can also accept a reference to a NotificationFilter and a "handback" Object to provide some context that is passed back with each Notification. Both of those attributes are optional. Extending the above example to include those attributes as well as an explicit MBeanServer bean name would produce the following:

 <jmx:notification-listening-channel-adapter id="adapter"

Since the notification-listening adapter is registered with the MBeanServer directly, it is event-driven and does not require any poller configuration.

29.2 Notification Publishing Channel Adapter

The Notification-publishing Channel Adapter is relatively simple. It only requires a JMX ObjectName in its configuration as shown below.


 <jmx:notification-publishing-channel-adapter id="adapter"

It does also require that an MBeanExporter be present in the context. That is why the <context:mbean-export/> element is shown above as well.

When Messages are sent to the channel for this adapter, the Notification is created from the Message content. If the payload is a String it will be passed as the "message" text for the Notification. Any other payload type will be passed as the "userData" of the Notification.

JMX Notifications also have a "type", and it should be a dot-delimited String. There are two ways to provide the type. Precedence will always be given to a Message header value associated with the JmxHeaders.NOTIFICATION_TYPE key. On the other hand, you can rely on a fallback "default-notification-type" attribute provided in the configuration.


 <jmx:notification-publishing-channel-adapter id="adapter"

29.3 Attribute Polling Channel Adapter

The attribute polling adapter is useful when you have a requirement to periodically check on some value that is available through an MBean as a managed attribute. The poller can be configured in the same way as any other polling adapter in Spring Integration (or it's possible to rely on the default poller). The "object-name" and "attribute-name" are required. An MBeanServer reference is also required, but it will automatically check for a bean named "mbeanServer" by default just like the notification-listening-channel-adapter described above.

 <jmx:attribute-polling-channel-adapter id="adapter"
     <si:poller max-messages-per-poll="1" fixed-rate="5000"/>

29.4 Operation Invoking Channel Adapter

The operation-invoking-channel-adapter enables Message-driven invocation of any managed operation exposed by an MBean. Each invocation requires the operation name to be invoked and the ObjectName of the target MBean. Both of these must be explicitly provided via adapter configuration:

 <jmx:operation-invoking-channel-adapter id="adapter"

Then the adapter only needs to be able to discover the "mbeanServer" bean. If a different bean name is required, then provide the "mbean-server" attribute with a reference.

The payload of the Message will be mapped to the parameters of the operation, if any. A Map-typed payload with String keys is treated as name/value pairs whereas a List or array would be passed as a simple argument list (with no explicit parameter names). If the operation requires a single parameter value, then the payload can represent that single value, and if the operation requires no parameters, then the payload would be ignored.

If you want to expose a channel for a single common operation to be invoked by Messages that need not contain headers, then that option works well.

29.5 Operation Invoking outbound Gateway

Similar to operation-invoking-channel-adapter Spring Integration also provides operation-invoking-outbound-gateway which could be used when dealing with non-void operations and return value is required. Such return value will be sent as message payload to the 'reply-channel' specified by this Gateway.

 <jmx:operation-invoking-outbound-gateway request-channel="requestChannel"

Another way of provideing the 'reply-channel' is by setting MessageHeaders.REPLY_CHANNEL Message Header

29.6 MBean Exporter

Spring Integration components themselves may be exposed as MBeans when the IntegrationMBeanExporter is configured. To create an instance of the IntegrationMBeanExporter, define a bean and provide a reference to an MBeanServer and a domain name (if desired). The domain can be left out in which case the default domain is "spring.application".

 <jmx:mbean-exporter domain="my.company.domain" mbean-server="mbeanServer"/>

 <bean id="mbeanServer" class="org.springframework.jmx.support.MBeanServerFactoryBean">
     <property name="locateExistingServerIfPossible" value="true"/>

The MBean exporter is orthogonal to the one provided in Spring core - it registers message channels and message handlers, but not itself (you can expose the exporter itself using the standard <context:mbean-export/> tag).

29.7 Control Bus

As described in (EIP), the idea behind the Control Bus is that the same messaging system can be used for monitoring and managing the components within the framework as is used for "application-level" messaging. In Spring Integration we build upon the adapters described above so that it's possible to send Messages as a means of invoking exposed operations. Internally, the Control Bus uses a Spring MBeanExporter instance to expose the various endpoints and channels. To create an instance of the Control Bus, define a bean and provide a reference to an MBeanServer and a domain name.

 <jmx:control-bus mbean-exporter="mbeanExporter" operation-channel="operationChannel"/>

 <jmx:mbean-exporter id="mbeanExporter" mbean-server="mbeanServer"/>

The Control Bus has an "operationChannel" that can be accessed for invoking operations on the MBeans that it has exported. This will also be covered by namespace support soon to make it easier to configure references to that channel for other producers. We will likely add some other channels for notifications and attribute polling as well.

The Control Bus functionality is a work in progress. At this time, one can perform some basic monitoring of Message Channels and/or invoke Lifecycle operations (start/stop) on Message Endpoints. Now that the foundation is available, however, we will be able to extend the attributes and operations that are being exposed.