How do I monitor the computer's CPU, memory, and disk usage in Java?

Along the lines of what I mentioned in this post. I recommend you use the SIGAR API. I use the SIGAR API in one of my own applications and it is great. You'll find it is stable, well supported, and full of useful examples. It is open-source with a GPL 2 Apache 2.0 license. Check it out. I have a feeling it will meet your needs.

Using Java and the Sigar API you can get Memory, CPU, Disk, Load-Average, Network Interface info and metrics, Process Table information, Route info, etc.

The following supposedly gets you CPU and RAM. See ManagementFactory for more details.

import java.lang.management.ManagementFactory;
import java.lang.management.OperatingSystemMXBean;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

private static void printUsage() {
  OperatingSystemMXBean operatingSystemMXBean = ManagementFactory.getOperatingSystemMXBean();
  for (Method method : operatingSystemMXBean.getClass().getDeclaredMethods()) {
    method.setAccessible(true);
    if (method.getName().startsWith("get")
        && Modifier.isPublic(method.getModifiers())) {
            Object value;
        try {
            value = method.invoke(operatingSystemMXBean);
        } catch (Exception e) {
            value = e;
        } // try
        System.out.println(method.getName() + " = " + value);
    } // if
  } // for
}

In JDK 1.7, you can get system CPU and memory usage via com.sun.management.OperatingSystemMXBean. This is different than java.lang.management.OperatingSystemMXBean.

long    getCommittedVirtualMemorySize()
Returns the amount of virtual memory that is guaranteed to be available to the running process in bytes, or -1 if this operation is not supported.

long    getFreePhysicalMemorySize()
Returns the amount of free physical memory in bytes.

long    getFreeSwapSpaceSize()
Returns the amount of free swap space in bytes.

double  getProcessCpuLoad()
Returns the "recent cpu usage" for the Java Virtual Machine process.

long    getProcessCpuTime()
Returns the CPU time used by the process on which the Java virtual machine is running in nanoseconds.

double  getSystemCpuLoad()
Returns the "recent cpu usage" for the whole system.

long    getTotalPhysicalMemorySize()
Returns the total amount of physical memory in bytes.

long    getTotalSwapSpaceSize()
Returns the total amount of swap space in bytes.