JDK1.8获取CPU利用率

可以使用Java Management Extensions（JMX）来获取CPU利用率。具体步骤如下：

1. 获取Java虚拟机的MBeanServer对象。

MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();

2. 获取操作系统的ObjectName对象。

ObjectName name = ObjectName.getInstance("java.lang:type=OperatingSystem");

3. 调用MBeanServer的方法获取操作系统的属性值，包括CPU利用率。

AttributeList list = mbs.getAttributes(name, new String[]{"ProcessCpuLoad", "SystemCpuLoad"});
if (list.isEmpty()) return Double.NaN;

Attribute att = (Attribute) list.get(0);
Double value = (Double) att.getValue();
// CPU利用率为value * 100.0

完整示例代码如下：

import java.lang.management.ManagementFactory;
import java.lang.management.OperatingSystemMXBean;
import java.lang.reflect.Method;
import javax.management.Attribute;
import javax.management.AttributeList;
import javax.management.MBeanServer;
import javax.management.ObjectName;

public class CPUMonitor {
    private static final int SLEEP_TIME = 500;

    public static void main(String[] args) throws Exception {
        MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
        ObjectName name = ObjectName.getInstance("java.lang:type=OperatingSystem");
        Method method = mbs.getClass().getMethod("getOperatingSystemMXBean");
        OperatingSystemMXBean os = (OperatingSystemMXBean) method.invoke(mbs);
        long prevUpTime = os.getProcessCpuTime();
        long prevSystemTime = System.nanoTime();
        while (true) {
            Thread.sleep(SLEEP_TIME);
            long upTime = os.getProcessCpuTime();
            long systemTime = System.nanoTime();
            double cpuUsage = (double) (upTime - prevUpTime) / (systemTime - prevSystemTime);
            cpuUsage *= os.getAvailableProcessors();
            cpuUsage *= 100.0;
            prevUpTime = upTime;
            prevSystemTime = systemTime;
            System.out.println("CPU Usage: " + String.format("%.2f%%", cpuUsage));
        }
    }
}