SystemInfo.java

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

public class SystemInfo {
	private static OperatingSystemMXBean sys = ManagementFactory.getOperatingSystemMXBean();
	private static Method getFreePhysicalMemorySize;
	private static Method getTotalPhysicalMemorySize;
	static{
		try {
			getFreePhysicalMemorySize = sys.getClass().getDeclaredMethod("getFreePhysicalMemorySize");
			getFreePhysicalMemorySize.setAccessible(true);
			getTotalPhysicalMemorySize = sys.getClass().getDeclaredMethod("getTotalPhysicalMemorySize");
			getTotalPhysicalMemorySize.setAccessible(true);
			//System.out.println("Used memory: " + ((long)getTotalPhysicalMemorySize.invoke(sys) - (long)getFreePhysicalMemorySize.invoke(sys)));
		} catch (NoSuchMethodException | SecurityException | IllegalArgumentException e) {
			e.printStackTrace();
		}
	}
	
	/**
	 * Get the system free memory, in bytes
	 * @return
	 * @throws IllegalAccessException
	 * @throws IllegalArgumentException
	 * @throws InvocationTargetException
	 */
	public static long getFreePhysicalMemorySize() throws IllegalAccessException, IllegalArgumentException, InvocationTargetException{
		return (long)getFreePhysicalMemorySize.invoke(sys);
	}
	
	/**
	 * Get the system total memory, in bytes
	 * @return
	 * @throws IllegalAccessException
	 * @throws IllegalArgumentException
	 * @throws InvocationTargetException
	 */
	public static long getTotalPhysicalMemorySize() throws IllegalAccessException, IllegalArgumentException, InvocationTargetException{
		return (long)getTotalPhysicalMemorySize.invoke(sys);
	}
	
	/**
	 * Get the system used memory, in bytes
	 * @return
	 * @throws IllegalAccessException
	 * @throws IllegalArgumentException
	 * @throws InvocationTargetException
	 */
	public static long getUsedPhysicalMemorySize() throws IllegalAccessException, IllegalArgumentException, InvocationTargetException{
		return (long)getTotalPhysicalMemorySize.invoke(sys)-(long)getFreePhysicalMemorySize.invoke(sys);
	}
	
	/**
	 * Get the system used memory, in bytes
	 * @return
	 * @throws IllegalAccessException
	 * @throws IllegalArgumentException
	 * @throws InvocationTargetException
	 */
	public static long getFreePhysicalMemorySizePercent() throws IllegalAccessException, IllegalArgumentException, InvocationTargetException{
		return (getFreePhysicalMemorySize()*100)/getTotalPhysicalMemorySize();
	}
}