{"id":630,"date":"2015-01-29T12:29:14","date_gmt":"2015-01-29T11:29:14","guid":{"rendered":"http:\/\/hirt.se\/blog\/?p=630"},"modified":"2015-01-29T12:29:14","modified_gmt":"2015-01-29T11:29:14","slug":"reading-jmx-metrics","status":"publish","type":"post","link":"https:\/\/hirt.se\/blog\/?p=630","title":{"rendered":"Reading JMX Metrics"},"content":{"rendered":"

I found this question on Stack Overflow about how to connect to a locally running process and read JMX metrics. I thought I\u2019d explain a little bit more in detail here on the blog. The steps involved are:<\/p>\n

    \n
      \n
    1. Try to get the JMX Service URL for the local JMX agent.<\/li>\n
    2. If you couldn\u2019t, try to start the local JMX agent.<\/li>\n
    3. Open an MBeanServerConnection to the local JMX agent.<\/li>\n
    4. Do whatever MBean-ish stuff you were planning on doing, for example reading attributes.<\/li>\n<\/ol>\n<\/ol>\n

      This is pretty much as simple as it sounds. Let\u2019s do them in order.<\/p>\n

      Getting the Service URL<\/h2>\n

      When the local management agent is started, it publishes the service URL (which also contains the serialized stub for communication \u2013 take a look at the URL, it\u2019s really quite funny) in a well known location. This can be retrieved by using the sun.management.ConnectorAddressLink class like this:<\/p>\n

      \n

      private static JMXServiceURL getLocalStubServiceURLFromPID(int pid)
              throws IOException {
          String address = ConnectorAddressLink.importFrom(pid);
          if (address != null) {
              return new JMXServiceURL(address);
          }
          return null;
      }<\/p>\n<\/blockquote>\n

      If you didn\u2019t get any service url, then the local management agent was not started. <\/p>\n

      Starting the Local Management Agent<\/h2>\n

      Starting the local management agent can be done in various ways. In late versions of the JDK this is quite easily done. I am only going to show you the simple way today. In older you might need to resort to the attach command to load java agents (VirtualMachine vm = VirtualMachine.attach(pid).loadAgent(<path to management-agent.jar>,\u201dcom.sun.management.jmxremote\u201d)).<\/p>\n

      To start the local agent, we simply execute the diagnostic command for starting it:<\/p>\n

      \n

      \u2026<\/p>\n

      executeCommandForPID(vm, pid, “ManagementAgent.start_local”); <\/p>\n

      \u2026 <\/p>\n

      private static void executeCommandForPID(VirtualMachine vm, String pid,
              String cmd) throws IOException {
          HotSpotVirtualMachine hsvm = (HotSpotVirtualMachine) vm;
          hsvm.executeJCmd(cmd);
      }<\/p>\n<\/blockquote>\n

        <\/p>\n

      Opening the MBeanServer Connection<\/h2>\n

      This, as well as doing the MBeany things you want to do once you have the connection, is done just as you would normally do it:<\/p>\n

      \n

      JMXConnector jmxc = JMXConnectorFactory.connect(url, null);
      MBeanServerConnection connection = jmxc.getMBeanServerConnection();<\/p>\n<\/blockquote>\n

      Getting attributes: <\/p>\n

      \n

      connection.getAttribute(“java.lang:type=Memory”, “HeapMemoryUsage”);<\/p>\n<\/blockquote>\n

        <\/p>\n

      <\/h2>\n

      Summary<\/h2>\n