How do I check CPU and Memory Usage in Java?

If you are looking specifically for memory in JVM:

Runtime runtime = Runtime.getRuntime();

NumberFormat format = NumberFormat.getInstance();

StringBuilder sb = new StringBuilder();
long maxMemory = runtime.maxMemory();
long allocatedMemory = runtime.totalMemory();
long freeMemory = runtime.freeMemory();

sb.append("free memory: " + format.format(freeMemory / 1024) + "<br/>");
sb.append("allocated memory: " + format.format(allocatedMemory / 1024) + "<br/>");
sb.append("max memory: " + format.format(maxMemory / 1024) + "<br/>");
sb.append("total free memory: " + format.format((freeMemory + (maxMemory - allocatedMemory)) / 1024) + "<br/>");

However, these should be taken only as an estimate...

import java.io.File;
import java.text.NumberFormat;

public class SystemInfo {

    private Runtime runtime = Runtime.getRuntime();

    public String info() {
        StringBuilder sb = new StringBuilder();
        sb.append(this.osInfo());
        sb.append(this.memInfo());
        sb.append(this.diskInfo());
        return sb.toString();
    }

    public String osName() {
        return System.getProperty("os.name");
    }

    public String osVersion() {
        return System.getProperty("os.version");
    }

    public String osArch() {
        return System.getProperty("os.arch");
    }

    public long totalMem() {
        return Runtime.getRuntime().totalMemory();
    }

    public long usedMem() {
        return Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory();
    }

    public String memInfo() {
        NumberFormat format = NumberFormat.getInstance();
        StringBuilder sb = new StringBuilder();
        long maxMemory = runtime.maxMemory();
        long allocatedMemory = runtime.totalMemory();
        long freeMemory = runtime.freeMemory();
        sb.append("Free memory: ");
        sb.append(format.format(freeMemory / 1024));
        sb.append("<br/>");
        sb.append("Allocated memory: ");
        sb.append(format.format(allocatedMemory / 1024));
        sb.append("<br/>");
        sb.append("Max memory: ");
        sb.append(format.format(maxMemory / 1024));
        sb.append("<br/>");
        sb.append("Total free memory: ");
        sb.append(format.format((freeMemory + (maxMemory - allocatedMemory)) / 1024));
        sb.append("<br/>");
        return sb.toString();

    }

    public String osInfo() {
        StringBuilder sb = new StringBuilder();
        sb.append("OS: ");
        sb.append(this.osName());
        sb.append("<br/>");
        sb.append("Version: ");
        sb.append(this.osVersion());
        sb.append("<br/>");
        sb.append(": ");
        sb.append(this.osArch());
        sb.append("<br/>");
        sb.append("Available processors (cores): ");
        sb.append(runtime.availableProcessors());
        sb.append("<br/>");
        return sb.toString();
    }

    public String diskInfo() {
        /* Get a list of all filesystem roots on this system */
        File[] roots = File.listRoots();
        StringBuilder sb = new StringBuilder();

        /* For each filesystem root, print some info */
        for (File root : roots) {
            sb.append("File system root: ");
            sb.append(root.getAbsolutePath());
            sb.append("<br/>");
            sb.append("Total space (bytes): ");
            sb.append(root.getTotalSpace());
            sb.append("<br/>");
            sb.append("Free space (bytes): ");
            sb.append(root.getFreeSpace());
            sb.append("<br/>");
            sb.append("Usable space (bytes): ");
            sb.append(root.getUsableSpace());
            sb.append("<br/>");
        }
        return sb.toString();
    }
}

If you are using the Sun JVM, and are interested in the internal memory usage of the application (how much out of the allocated memory your app is using) I prefer to turn on the JVMs built-in garbage collection logging. You simply add -verbose:gc to the startup command.

From the Sun documentation:

The command line argument -verbose:gc prints information at every collection. Note that the format of the -verbose:gc output is subject to change between releases of the J2SE platform. For example, here is output from a large server application:

[GC 325407K->83000K(776768K), 0.2300771 secs]
[GC 325816K->83372K(776768K), 0.2454258 secs]
[Full GC 267628K->83769K(776768K), 1.8479984 secs]

Here we see two minor collections and one major one. The numbers before and after the arrow

325407K->83000K (in the first line)

indicate the combined size of live objects before and after garbage collection, respectively. After minor collections the count includes objects that aren't necessarily alive but can't be reclaimed, either because they are directly alive, or because they are within or referenced from the tenured generation. The number in parenthesis

(776768K) (in the first line)

is the total available space, not counting the space in the permanent generation, which is the total heap minus one of the survivor spaces. The minor collection took about a quarter of a second.

0.2300771 secs (in the first line)

For more info see: http://java.sun.com/docs/hotspot/gc5.0/gc_tuning_5.html

From here

    OperatingSystemMXBean operatingSystemMXBean = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
    RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
    int availableProcessors = operatingSystemMXBean.getAvailableProcessors();
    long prevUpTime = runtimeMXBean.getUptime();
    long prevProcessCpuTime = operatingSystemMXBean.getProcessCpuTime();
    double cpuUsage;
    try
    {
        Thread.sleep(500);
    }
    catch (Exception ignored) { }

    operatingSystemMXBean = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
    long upTime = runtimeMXBean.getUptime();
    long processCpuTime = operatingSystemMXBean.getProcessCpuTime();
    long elapsedCpu = processCpuTime - prevProcessCpuTime;
    long elapsedTime = upTime - prevUpTime;

    cpuUsage = Math.min(99F, elapsedCpu / (elapsedTime * 10000F * availableProcessors));
    System.out.println("Java CPU: " + cpuUsage);

JMX, The MXBeans (ThreadMXBean, etc) provided will give you Memory and CPU usages.

OperatingSystemMXBean operatingSystemMXBean = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
operatingSystemMXBean.getSystemCpuLoad();

For memory usage, the following will work,

long total = Runtime.getRuntime().totalMemory();
long used  = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory();

For CPU usage, you'll need to use an external application to measure it.

Since Java 1.5 the JDK comes with a new tool: JConsole wich can show you the CPU and memory usage of any 1.5 or later JVM. It can do charts of these parameters, export to CSV, show the number of classes loaded, the number of instances, deadlocks, threads etc...

Java's Runtime object can report the JVM's memory usage. For CPU consumption you'll have to use an external utility, like Unix's top or Windows Process Manager.

If you use the runtime/totalMemory solution that has been posted in many answers here (I've done that a lot), be sure to force two garbage collections first if you want fairly accurate/consistent results.

For effiency Java usually allows garbage to fill up all of memory before forcing a GC, and even then it's not usually a complete GC, so your results for runtime.freeMemory() always be somewhere between the "real" amount of free memory and 0.

The first GC doesn't get everything, it gets most of it.

The upswing is that if you just do the freeMemory() call you will get a number that is absolutely useless and varies widely, but if do 2 gc's first it is a very reliable gauge. It also makes the routine MUCH slower (seconds, possibly).

JConsole is an easy way to monitor a running Java application or you can use a Profiler to get more detailed information on your application. I like using the NetBeans Profiler for this.

Here is some simple code to calculate the current memory usage in megabytes:

double currentMemory = ( (double)((double)(Runtime.getRuntime().totalMemory()/1024)/1024))- ((double)((double)(Runtime.getRuntime().freeMemory()/1024)/1024));

I would also add the following way to track CPU Load:

import java.lang.management.ManagementFactory;
import com.sun.management.OperatingSystemMXBean;

double getCpuLoad() {
    OperatingSystemMXBean osBean =
        (com.sun.management.OperatingSystemMXBean) ManagementFactory.
        getPlatformMXBeans(OperatingSystemMXBean.class);
    return osBean.getProcessCpuLoad();
}

You can read more here

The YourKit Java profiler is an excellent commercial solution. You can find further information in the docs on CPU profiling and memory profiling.

If you are using Tomcat, check out Psi Probe, which lets you monitor internal and external memory consumption as well as a host of other areas.

For Eclipse, you can use TPTP (Test and Performance Tools Platform) for analyse memory usage and etc. more information

I want to add a note to the existing answers:

These methods only keep track of JVM Memory. The actual process may consume more memory.

java.nio.ByteBuffer.allocateDirect() is a function/library, that is easily missed, and indeed allocated native memory, that is not part of the Java memory management.

On Linux, you may use something like this to get the actually consumed memory: https://linuxhint.com/check_memory_usage_process_linux/