Querying swap space in java 9

Question

Due to a bug in the sigar library version I am using (returns bogus values for swap), I tried using com.sun.management.OperatingSystemMXBean instead. This worked fine and gave me the desired results (on Windows).

Class<?> sunMxBeanClass = Class.forName("com.sun.management.OperatingSystemMXBean");
sunMxBeanInstance = sunMxBeanClass.cast(ManagementFactory.getOperatingSystemMXBean());
getFreeSwapSpaceSize = getMethodWithName(sunMxBeanClass, "getFreeSwapSpaceSize");
getTotalSwapSpaceSize = getMethodWithName(sunMxBeanClass, "getTotalSwapSpaceSize");

However this breaks with java 9. Is there another way to query swap file / partition information using java? I don't want to introduce a new library or version of sigar.

Cross platform solutions appreciated but windows is enough :--)

Thanks

Bedrock

Answer 1

You may try to discover available MX attributes dynamically:

public class ExtendedOsMxBeanAttr {
    public static void main(String[] args) {
        String[] attr={ "TotalPhysicalMemorySize", "FreePhysicalMemorySize",
                        "FreeSwapSpaceSize", "TotalSwapSpaceSize"};
        OperatingSystemMXBean op = ManagementFactory.getOperatingSystemMXBean();
        List<Attribute> al;
        try {
            al = ManagementFactory.getPlatformMBeanServer()
                                  .getAttributes(op.getObjectName(), attr).asList();
        } catch (InstanceNotFoundException | ReflectionException ex) {
            Logger.getLogger(ExtendedOsMxBeanAttr.class.getName())
                  .log(Level.SEVERE, null, ex);
            al = Collections.emptyList();
        }
        for(Attribute a: al) {
            System.out.println(a.getName()+": "+a.getValue());
        }
    }
}

There is no dependency to com.sun classes here, not even a reflective access.

Factory

Answer 2

The jdk.management module exports the com.sun.management API and it works the same way in JDK 9 as it did in JDK 8. So either of the following should work:

com.sun.management.OperatingSystemMXBean mbean
    = (com.sun.management.OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
long free = mbean.getFreePhysicalMemorySize();
long swap = mbean.getTotalSwapSpaceSize();

or

OperatingSystemMXBean mbean = ManagementFactory.getOperatingSystemMXBean();
Class<?> klass = Class.forName("com.sun.management.OperatingSystemMXBean");
Method freeSpaceMethod = klass.getMethod("getFreeSwapSpaceSize");
Method totalSpaceMethod = klass.getMethod("getTotalSwapSpaceSize");
long free = (long) freeSpaceMethod.invoke(mbean);
long swap = (long) totalSpaceMethod.invoke(mbean);

Morose

Might be worth to emphasize that there are two different (easy to confuse) modules, java.management and jdk.management. Using the latter inevitably adds more dependencies to an application, but makes com.sun.management.OperatingSystemMXBean directly available. Using the former requires dynamic discovery of these extensions. (Why they don’t just offer these properties in the base interface is above me; it’s not as if there weren’t already tons of optional properties…) – Factory