Eamonn McManus's Blog

JMX API 2.0 Early Draft Review

The first draft of JSR 255 is out! This defines version 2.0 of the JMX API. We're planning to integrate it into the Java SE 7 platform, subject to the approval of the Expert Group for that platform.

Here's a summary of the important changes. If you're interested, I'd encourage you to download the draft and look at the summary in the Overview Description, which has links into the relevant parts of the API.

This draft contains all the major features that we are planning to add in this version of the API. If there's anything you'd like to see changed, this would be a very good time to let us know!

Namespaces and Cascading

The concept of namespaces is new. All MBeans whose domain begins with foo//, for example foo//com.example:type=CacheController, belong to the namespace foo//. Previously, MBeanServer.queryNames(null, null)) returned a list of all MBeans. Now, MBeans within namespaces do not appear in that list. Additionally, namespaces can contain Virtual MBeans which do not have to exist as Java objects when they are not being accessed. Namespaces allow much improved scalability, especially when accessing certain MBeans is expensive.

Cascading or Federation means that it is straightforward to import MBeans from a remote MBean Server as if they were local. This blog entry gives an overview of what Cascading is about.

Event Service and Notifications

The Event Service provides greater control over notification handling than the default technique using MBeanServer.addNotificationListener. The Event Service separates the logic for notification handling from the particular connector that you are using. You can transport notifications using that connector, or using a completely different transport. See the description of the javax.management.event package for more information.

A new class QueryNotificationFilter allows notifications to be filtered using the existing query subsystem.

Resource injection provides an alternative to implementing the NotificationBroadcaster interface or extending the NotificationBroadcasterSupport class. See the next section.

Annotations and Resource Injection

MBeans can now be defined using annotations. Also, the @Resource annotation allows an MBean to get a reference to its MBeanServer and ObjectName references, as an alternative to implementing MBeanRegistration.

This blog entry provides details and rationale.

Client Contexts and Localization

MBeans now have access to a context that can contain information such as locale or transaction ids. (Note though that there is no explicit support for transactions in the API.)

The descriptions in an MBeanInfo can be localized using a new method MBeanInfo.localizeDescriptions. A way will be provided to cause this method to be called for all MBeans, using a locale communicated by a remote client. The details are still being sorted out so this area of the API will change.

Queries

A new Query Language provides an alternative way to specify queries that is often simpler than constructing QueryExp objects using the static methods of the Query class. (The idea of an SQL-like query language for JMX queries was first proposed by Norbert Lataille and Marc Fleury in 2000, although the language in this draft is not derived from that proposal.)

Attributes appearing in a query can now use a dot (.) to specify a value contained in an attribute of complex type, similar to the existing support in the javax.management.monitor package.

MXBeans

The type mappings can now be customized for any MXBean using annotations or options. Previously the mapping rules were fixed.

Options for StandardMBean and Proxies

A new MBeanOptions class provides control over details of StandardMBean and MXBean proxy operation.

DynamicWrapperMBean

A new interface DynamicWrapperMBean gives better behaviour for MBeans that wrap other objects, in particular as regards class loading.

NotificationManager interface

Three methods of the MBeanServerConnection interface are promoted to a new parent interface NotificationManager, which can be implemented by classes such as EventClient that provide addNotificationListener/removeNotificationListener functionality.

Model MBeans

It is no longer required that the Descriptor in, for example, ModelMBeanAttributeInfo contain redundant descriptorType and name fields. The previously-required values are supplied by default if omitted. (Thanks to Lars Westergren for this contribution.)

Send feedback!

Feel free to comment here, or send mail to jmx-spec-comments@sun.com.

[Tags: jmx jsr jsr255 jcp edr]

Comments

• "Cascading or Federation means that it is straightforward to import MBeans from a remote MBean Server as if they were local.."

  but this means that cascading also virtualize connection and synchronization with remote mbeanServer? i.e. what happens if connection with remote mbServer goes down, or an Mbean mirrored has been unregistered from its remote mbeanServer?

  thanks

  Posted by: lukebike on February 14, 2008 at 12:42 AM

• These are excellent questions, and we have given considerable thought to them. The blog entry I referenced described an implementation where the imported MBeans were represented by "mirror MBeans" locally, which means you do have to decide how synchronization works. But the design in the JMX API makes use of the new namespace support so that for example a reference to foo//bar:type=Baz can be forwarded directly to the remote server that is federated as "foo", where it is seen as a reference to bar:type=Baz. That means that if an MBean is unregistered from the remote server then it is immediately inaccessible in the local server too, and if the connection to the remote server breaks then accesses to its MBeans will get exceptions. You can also add a listener to the namespace in order to be informed when the connection breaks. See the class javax.management.namespaces.JMXServiceURLNamespace in the API documentation.

  Posted by: emcmanus on February 14, 2008 at 01:07 AM

• maybe it's a stupid question, but where can I download jmx2.0 jar??
  thanks

  Posted by: lukebike on February 14, 2008 at 07:11 AM

• Not a stupid question at all. The jar currently isn't available publicly but we're working on it. Stay tuned!

  Posted by: emcmanus on February 14, 2008 at 07:22 AM

• ok!

  Posted by: lukebike on February 14, 2008 at 07:40 AM

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