How do I access memory usage programmatically via JMX?

Question

I'm looking for sample Java JMX code to access the values of JMX attributes from another VM.

With JConsole, I have no problem looking at java.lang/Memory/Attributes/HeapMemory

How would I get the same information from a Java program running in a VM?

Examples of any command line options needed, or other things that need to be started appreciated.

Answer 1

You need to setup a JMXConnector. Here is a code snippet that will get the committed heap memory usage on a remote machine.

String host ="myHost";
int port = 1234;
HashMap map = new HashMap();
String[] credentials = new String[2];
credentials[0] = user;
credentials[1] = password;
map.put("jmx.remote.credentials", credentials);
JMXConnector c = JMXConnectorFactory.newJMXConnector(createConnectionURL(host, port), map);
c.connect();
Object o = c.getMBeanServerConnection().getAttribute(new ObjectName("java.lang:type=Memory"), "HeapMemoryUsage");
CompositeData cd = (CompositeData) o;
System.out.println(cd.get("committed"));

private static JMXServiceURL createConnectionURL(String host, int port) throws MalformedURLException
{
    return new JMXServiceURL("rmi", "", 0, "/jndi/rmi://" + host + ":" + port + "/jmxrmi");
}

If you don't care about security you can set the map to null. You need to start up the remote server with;

-Dcom.sun.management.jmxremote.port=1234
-Dcom.sun.management.jmxremote.authenticate=false
-Dcom.sun.management.jmxremote.ssl=false

You might want to take a look at wlshell which is a small utility that allows you to access MBeans on a remote server using a text interface or a script, It can be used with WebLogic, but it works for any Java program where you have enabled remote monitoring.

Answer 2

@Kire's answer looks good but I thought I'd add some details about my SimpleJMX package. It contains server support that allows you to export beans easily and also includes a simple client interface that works against any JVM that exports JMX information.

To access memory usage you'd do something like:

JmxClient client = new JmxClient("some.host.name", somePortNumber);
// get the memory composite information
CompositeData composite =
      (CompositeData)client.getAttribute(new ObjectName("java.lang:type=Memory"),
                                         "HeapMemoryUsage");
System.out.println(composite.get("committed"));

Answer 3

// Retrieve memory managed bean from management factory.
MemoryMXBean memBean = ManagementFactory.getMemoryMXBean() ;
MemoryUsage heap = memBean.getHeapMemoryUsage();
MemoryUsage nonHeap = memBean.getNonHeapMemoryUsage();

// Retrieve the four values stored within MemoryUsage:
// init: Amount of memory in bytes that the JVM initially requests from the OS.
// used: Amount of memory used.
// committed: Amount of memory that is committed for the JVM to use.
// max: Maximum amount of memory that can be used for memory management.
System.err.println(String.format("Heap: Init: %d, Used: %d, Committed: %d, Max.: %d",
  heap.getInit(), heap.getUsed(), heap.getCommitted(), heap.getMax()));
System.err.println(String.format("Non-Heap: Init: %d, Used: %d, Committed: %d, Max.: %d",
  nonHeap.getInit(), nonHeap.getUsed(), nonHeap.getCommitted(), nonHeap.getMax()));

Answer 4

This is how you get the MemoryMXBean remotely (to complement @Adamski's answer):

MemoryMXBean memoryMXBeanProxy = JMX.newMXBeanProxy(
            conn, new ObjectName("java.lang:type=Memory"), MemoryMXBean.class);