
 
        Returns the ModelMBean's descriptor which contains MBean wide policies.  This descriptor contains
 metadata about the MBean and default policies for persistence and caching.
 
 The fields in the descriptor are defined, but not limited to, the following: 
 
 name           : MBean name  
 descriptorType : must be "mbean"   
 displayName    : name of attribute to be used in displays 
 persistPolicy  : OnUpdate|OnTimer|NoMoreOftenThan|OnUnregister|Always|Never  
 persistLocation : The fully qualified directory name where the MBean should be persisted (if appropriate)
 persistFile    : File name into which the MBean should be persisted
 persistPeriod  : seconds - frequency of persist cycle for OnTime and NoMoreOftenThan PersistPolicy 
 currencyTimeLimit : how long value is valid, <0 never, =0 always, >0 seconds  
 log            : where t: log all notifications f: log no notifications
 logfile        : fully qualified filename to log events to
 visibility     : 1-4 where 1: always visible 4: rarely visible
 export         : name to be used to export/expose this MBean so that it is findable by
                  other JMX Agents.   
 presentationString : xml formatted string to allow presentation of data to be associated with the MBean. 
 
 
 The default descriptor is: name=mbeanName,descriptorType=mbean, displayName=this.getClassName(), 
        persistPolicy=never,log=F,export=F,visibility=1
 If the descriptor does not contain all these fields, they will be added with these default values.
 
Note: because of inconsistencies in previous versions of
 this specification, it is recommended not to use negative or zero
 values for currencyTimeLimit.  To indicate that a
 cached value is never valid, omit the
 currencyTimeLimit field.  To indicate that it is
 always valid, use a very large number for this field.
        
        
Returns:
    the MBean descriptor. 
Throws:
  - 
MBeanException - Wraps a distributed communication
 Exception.
  - 
RuntimeOperationsException - a {@link
 RuntimeException} occurred while getting the descriptor.
See Also:
  ModelMBeanInfo.setMBeanDescriptor(javax.management.Descriptor),