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What is the purpose of JMX and what is it used for? I have been scanning through some of the tutorials on JMX and all they do is register some Mbeans and invoke those Mbeans from jconsole. If that is its purpose, then what is the difference between JMX and RMI (remote procedure call)?

Thanks in advance!

Mihai Todor
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hnm
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3 Answers3

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JMX architecture.

Yes in JMX we register our objects in mbean server using the ObjectName and objectReference. We can then change attributes or invoke methods remotely.

A connector makes a Java Management Extensions (JMX) technology MBean server accessible to remote Java technology-based clients.Many different implementations of connectors are possible. In particular, there are many possibilities for the protocol used to communicate over a connection between client and server.Some Connectors defined by the JMX Remote API specification are

  • "RMI Connector": This standard Remote Method Invocation (RMI) protocol must be supported by every implementation that conforms to the JMX Remote API standard.
  • "Generic Connector": The JMX Remote API standard also defines an optional protocol based directly on TCP sockets, called the JMX Messaging Protocol (JMXMP). An implementation of the standard can omit the JMXMP connector, but must not omit the RMI connector. The Java SE platform does not include the optional JMXMP connector.
  • "User-Defined Protocols": A connector can also implement a protocol that is not defined in the JMX technology.

If you look at the above architecture a connector provides full remote access to the MBeanServer API using various communication frameworks (RMI, IIOP, JMS, WS-* …), while an adaptor adapts the API to another protocol (SNMP, …) or to Web-based GUI (HTML/HTTP, WML/HTTP, …).

Generally we use JMX connectors to connect to the MBean server but we can chose other connectors as well.

To sum up JMX is an java technology and RMI is for Remote Method Invocation a Java specific implementation of a Remote Procedure Call interface which can be used in the JMX to communicated remotely.

Aniket Thakur
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'Remote Procedure Call' is a distributed computing concept where a process running on one host can call a procedure on another remote host. RMI in Java is one implementation of this concept.

MBeans are bean classes that can be registered with a JMX bus to listen to events arriving on the bus or to send events on the bus or to collect various sorts of data from the other participating Mbeans etc. It is most often used for health monitoring of application servers etc. It can check the number of active connections, amount of free memory and many other statistics to an analysis engine. And yes, they can be invoked remotely using an RPC mechanism. This is vital to its functioning as data collectors since in a cluster of application servers the data has to be fetched from all the collectors and collated at one place for analysis.

rahulmohan
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  • Thanks for the response.One more related question, can't we use RMI for same purpose? – hnm Feb 24 '11 at 05:55
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    @hnm: RMI deals with calling a method remotely and nothing more than that. i.e it gives you a stub class which serializes the input parameters, encodes the call as data, sends the data across the wire, where a server-side entity called the skeleton gets the data, decodes it to understand which method to be called on which class on the server side process and makes the call. Once the call is complete, the output parameters or exceptions are serialized by the skeleton and sent back to the stub which again deserializes it to return it to the calling program. Its just a mechanism for remote call. – rahulmohan Feb 24 '11 at 06:26
  • @hnm: (continuation) MBeans are the special classes that interact with the application being monitored and gives methods to retrieve the data. Those methods can theoritically, be called using RMI. But the JMX mechanism provides much nicer way of doing the same thing. – rahulmohan Feb 24 '11 at 06:35
  • @rahulmohan I have seen Apache Tomcat use JMX. Does JMX provides daemon objects as well? – Jay Nov 18 '16 at 02:55
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JMX is a generic API for publishing an interface to monitor the internals of a Java application ( A Java version of SNMP ).

RMI is for Remote Method Invocation a Java specific implementation of a Remote Procedure Call interface, they are not related at all.