I have this code to read physical memory: 

```
com.sun.management.OperatingSystemMXBean os = (com.sun.management.OperatingSystemMXBean)ManagementFactory.getOperatingSystemMXBean();
long physicalMemorySize =os.getTotalPhysicalMemorySize();
System.out.println("physicalMemorySize="+physicalMemorySize);

```

I have JDK 1.8.0\_121 (64bit, on Windows)  

This code is compiled without problem, and I can run it in console application, it runs OK.  

But when I put this code to some Bean or JSP page on WildFly 10 server, it shows error: 

```
Caused by: java.lang.ClassNotFoundException: com.sun.management.OperatingSystemMXBean

```

WildFly uses exactly the same JDK, so it should see this class like console application sees it.  

That class is in `jdk1.8.0_121\jre\lib\rt.jar` so I do not understand why WildFly complains about that ClassNotFoundException. 

What's the problem?
How to make WildFly run that code?