How to get cpu usage in java.

Getting cpu usage in java instance, that limits in executing java virtual machine, not os.

Have a look at the java class sun.tools.jconsole.SummaryTab.java in open JDK7 or source in web.(http://www.docjar.com/html/api/sun/tools/jconsole/SummaryTab$Result.java.html)

If you know JConsole, you know that cpu usages graph. that source is below.

  354       private static class CPUOverviewPanel extends OverviewPanel {

  355           private long prevUpTime, prevProcessCpuTime;

  356   

  357           CPUOverviewPanel() {

  358               super(getText("CPU Usage"), cpuUsageKey, cpuUsageName, Plotter.Unit.PERCENT);

  359               getPlotter().setDecimals(CPU_DECIMALS);

  360           }

  361   

  362           public void updateCPUInfo(Result result) {

  363               if (prevUpTime > 0L && result.upTime > prevUpTime) {

  364                   // elapsedCpu is in ns and elapsedTime is in ms.

  365                   long elapsedCpu = result.processCpuTime - prevProcessCpuTime;

  366                   long elapsedTime = result.upTime - prevUpTime;

  367                   // cpuUsage could go higher than 100% because elapsedTime

  368                   // and elapsedCpu are not fetched simultaneously. Limit to

  369                   // 99% to avoid Plotter showing a scale from 0% to 200%.

  370                   float cpuUsage =

  371                       Math.min(99F,

  372                                elapsedCpu / (elapsedTime * 10000F * result.nCPUs));

  373   

  374                   getPlotter().addValues(result.timeStamp,

  375                                   Math.round(cpuUsage * Math.pow(10.0, CPU_DECIMALS)));

  376                   getInfoLabel().setText(getText(cpuUsageFormat,

  377                                                  String.format("%."+CPU_DECIMALS+"f", cpuUsage)));

  378               }

  379               this.prevUpTime = result.upTime;

  380               this.prevProcessCpuTime = result.processCpuTime;

  381           }

  382       }

So. I made my own class to get java-cpu usage.

private void _getJavaRuntime() {

OperatingSystemMXBean osbean = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();

RuntimeMXBean runbean = (RuntimeMXBean) ManagementFactory.getRuntimeMXBean();

int nCPUs = osbean.getAvailableProcessors();

long prevUpTime = runbean.getUptime();

long prevProcessCpuTime = osbean.getProcessCpuTime();

try {

Thread.sleep(500);

} catch (Exception e) { }

osbean = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();

long upTime = runbean.getUptime();

long processCpuTime = osbean.getProcessCpuTime();

if (prevUpTime > 0L && upTime > prevUpTime) {

long elapsedCpu = processCpuTime - prevProcessCpuTime;

long elapsedTime = upTime - prevUpTime;

javacpu = Math.min(99F, elapsedCpu / (elapsedTime * 10000F * nCPUs));

} else {

javacpu = 0.001;

}

uptime = runbean.getUptime(); 

}