Unable to get OS Name from VIX Api

In my ESX Server, there are number of VM’s, I am trying to get the Name of OS from each VM’s using VIX API in Java.

Syntax:

osName = vixVmHandle.readVariable("guestOS",VixConstants.VIX_VM_CONFIG_RUNTIME_ONLY);

Any one have idea about this, please let me know.

Thanks in advance.