Java program to print out open / max file descriptors

Descriptors.java

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

class Descriptors {
    public static void main(String [ ] args) {
        OperatingSystemMXBean osMxBean = ManagementFactory.getOperatingSystemMXBean();
        try {
            Method getMaxFileDescriptorCountField = osMxBean.getClass().getDeclaredMethod("getMaxFileDescriptorCount");
            Method getOpenFileDescriptorCountField = osMxBean.getClass().getDeclaredMethod("getOpenFileDescriptorCount");
            getMaxFileDescriptorCountField.setAccessible(true);
            getOpenFileDescriptorCountField.setAccessible(true);
            System.out.println(getOpenFileDescriptorCountField.invoke(osMxBean) + "/" + getMaxFileDescriptorCountField.invoke(osMxBean));
        } catch (Exception e) {}
    }
}

This is very useful - used it to diagnose a limit of 4096 file descriptors on a Linux system that claims its limit is 2.4 million.