Retrieving JMX information for a Java process is very easy when using a tool such as JConsole or JVisualVM. These provide an interface that allows viewing of information such as CPU usage, memory usage, threads active and more. This blog post gives an example of how to retrieve such information programmatically.

In order to retrieve JMX information from a Java application, the target application must be configured to expose JMX information. This link shows how to do this.

As an example, we shall be retrieving CPU and memory usage from a standalone Mule instance. In Mule, the JMX agent may be configured from a Mule configuration file. Through this, one may set the address that a JMX client can use to retrieve information; this is how.

The following Java code allows for polling the JMX agent and retrieving memory, CPU usage and also shows how to remotely invoke the garbage collector:

// create jmx connection with mules jmx agent
JMXServiceURL url = new JMXServiceURL("service:jmx:rmi:///jndi/rmi://localhost:1098/server");
JMXConnector jmxc = JMXConnectorFactory.connect(url, null);
jmxc.connect();
 
//create object instances that will be used to get memory and operating system Mbean objects exposed by JMX; create variables for cpu time and system time before
Object memoryMbean = null;
Object osMbean = null;
long cpuBefore = 0;
long tempMemory = 0;
CompositeData cd = null;
 
cpuBefore = Long.parseLong(a.toString());
 
// call the garbage collector before the test using the Memory Mbean
jmxc.getMBeanServerConnection().invoke(new ObjectName("java.lang:type=Memory"), "gc", null, null);
 
//create a loop to get values every second (optional)
for (int i = 0; i < samplesCount; i++) {
 
//get an instance of the HeapMemoryUsage Mbean
memoryMbean = jmxc.getMBeanServerConnection().getAttribute(new ObjectName("java.lang:type=Memory"), "HeapMemoryUsage");
cd = (CompositeData) memoryMbean;
//get an instance of the OperatingSystem Mbean
osMbean = jmxc.getMBeanServerConnection().getAttribute(new ObjectName("java.lang:type=OperatingSystem"),"ProcessCpuTime");
System.out.println("Used memory: " + " " + cd.get("used") + " Used cpu: " + osMbean); //print memory usage
tempMemory = tempMemory + Long.parseLong(cd.get("used").toString());
Thread.sleep(1000); //delay for one second
}
 
//get system time and cpu time from last poll
long cpuAfter = Long.parseLong(osMbean.toString());
 
long cpuDiff = cpuAfter - cpuBefore; //find cpu time between our first and last jmx poll
System.out.println("Cpu diff in milli seconds: " + cpuDiff / 1000000); //print cpu time in miliseconds
System.out.println("average memory usage is: " + tempMemory / samplesCount);//print average memory usage

The above example prints:

...
Used memory: 23376624 Used cpu: 38060000000
Used memory: 24020624 Used cpu: 38080000000
Used memory: 24621920 Used cpu: 38090000000
Cpu diff in milli seconds: 4230
average memory usage is: 28028204

When the JMX agent may not be enabled for a Java process, it is also possible to retrieve information by fetching the process by id, for example. The following code shows how to do this using Sigar API:

//create a sigar object
Sigar sigar = new Sigar();
 
for (int i = 0; i < 100; i++) {
 
ProcessFinder find = new ProcessFinder(sigar);
//get the list of current java processes, and optionally query the list to choose which process to monitor
long[] pidList = sigar.getProcList();
//assuming we know the process id, we may query the process finder
long pid = find.findSingleProcess("Pid.Pid.eq=54730");
//get memory info for the process id
ProcMem memory = new ProcMem();
memory.gather(sigar, pid);
//get cou info for the oricess id
ProcCpu cpu = new ProcCpu();
cpu.gather(sigar, pid);
//print the memory used by the process id
System.out.println("Current memory used: " + Long.toString(memory.getSize()));
//print all memory info
System.out.println(memory.toMap());
//print all cpu info
System.out.println(cpu.toMap());
Thread.sleep(1000);
}

This is displayed when running the above example:

Current memory used: 3257659392
{Resident=258789376, PageFaults=109613, Size=3257659392}
{User=34973, LastTime=1404467787774, Percent=0.0, StartTime=1404467383826, Total=38121, Sys=3148}