javax.management.modelmbean

Provides the definition of the ModelMBean classes. A Model MBean is an MBean that acts as a bridge between the management interface and the underlying managed resource. Both the management interface and the managed resource are specified as Java objects. The same Model MBean implementation can be reused many times with different management interfaces and managed resources, and it can provide common functionality such as persistence and caching.

A Model MBean implements the {@link javax.management.modelmbean.ModelMBean ModelMBean} interface. It is a {@link javax.management.DynamicMBean DynamicMBean} whose {@link javax.management.DynamicMBean#getMBeanInfo() getMBeanInfo} method returns an object implementing {@link javax.management.modelmbean.ModelMBeanInfo ModelMBeanInfo}.

Every MBean has an {@link javax.management.MBeanInfo MBeanInfo} with information about the MBean itself, and its attributes, operations, constructors, and notifications. A Model MBean augments this MBeanInfo with {@link javax.management.Descriptor Descriptor}s that encode additional information in the form of (key,value) pairs. Usually, Descriptors are instances of {@link javax.management.modelmbean.DescriptorSupport DescriptorSupport}.

The class {@link javax.management.modelmbean.RequiredModelMBean RequiredModelMBean} provides a standard Model MBean implementation.

The following example shows a Model MBean being used to make the get method of a HashMap available for management through an MBean server. No other methods are available through the MBean server. There is nothing special about HashMap here. Public methods from any public class can be exposed for management in the same way.

import java.lang.reflect.Method;
import java.util.HashMap;
import javax.management.*;
import javax.management.modelmbean.*;

// ...

MBeanServer mbs = MBeanServerFactory.createMBeanServer();
// The MBean Server

HashMap map = new HashMap();
// The resource that will be managed

// Construct the management interface for the Model MBean
Method getMethod = HashMap.class.getMethod("get", new Class[] {Object.class});
ModelMBeanOperationInfo getInfo =
    new ModelMBeanOperationInfo("Get value for key", getMethod);
ModelMBeanInfo mmbi =
    new ModelMBeanInfoSupport(HashMap.class.getName(),
			      "Map of keys and values",
			      null,  // no attributes
			      null,  // no constructors
			      new ModelMBeanOperationInfo[] {getInfo},
			      null); // no notifications

// Make the Model MBean and link it to the resource
ModelMBean mmb = new RequiredModelMBean(mmbi);
mmb.setManagedResource(map, "ObjectReference");

// Register the Model MBean in the MBean Server
ObjectName mapName = new ObjectName(":type=Map,name=whatever");
mbs.registerMBean(mmb, mapName);

// Resource can evolve independently of the MBean
map.put("key", "value");

// Can access the "get" method through the MBean Server
mbs.invoke(mapName, "get", new Object[] {"key"}, new String[] {Object.class.getName()});
// returns "value"
    

Package Specification

• See the JMX 1.4 Specification PDF document available from the Java SE 6 Platform documentation on JMX

The fields in the descriptor are defined, but not limited to, the following:

 name           : attribute name
 descriptorType : must be "attribute"
 value          : current value for attribute
 default        : default value for attribute
 displayName    : name of attribute to be used in displays
 getMethod      : name of operation descriptor for get method
 setMethod      : name of operation descriptor for set method
 protocolMap    : object which implements the Descriptor interface: mappings
 must be appropriate for the attribute
 and entries can be updated or augmented at runtime.
 persistPolicy  : OnUpdate|OnTimer|NoMoreOftenThan|OnUnregister|Always|Never
 persistPeriod  : seconds - frequency of persist cycle.

 The fields in the descriptor are defined, but not limited to, the following: 

 name           : constructor name
 descriptorType : must be "operation"
 role           : must be "constructor"
 displayName    : human readable name of constructor
 visibility            : 1-4 where 1: always visible 4: rarely visible
 presentationString :  xml formatted string to describe how to present operation
 

The persistPolicy and currencyTimeLimit fields are meaningless for constructors, but are not considered invalid.

The default descriptor will have the name , descriptorType , displayName and role fields.

The fields in the descriptor are defined, but not limited to, the following:

 name           : notification name
 descriptorType : must be "notification"
 severity       : 0-6 where 0: unknown; 1: non-recoverable;
 2: critical, failure; 3: major, severe;
 4: minor, marginal, error; 5: warning;
 6: normal, cleared, informative
 messageID      : unique key for message text (to allow translation,
 analysis)
 messageText    : text of notification
 log            : T - log message F - do not log message
 logfile        : string fully qualified file name appropriate for
 operating system
 visibility     : 1-4 where 1: always visible 4: rarely visible
 presentationString : xml formatted string to allow presentation of data
 

 The fields in the descriptor are defined, but not limited to, the following:
 name           : operation name
 descriptorType : must be "operation"
 class          : class where method is defined (fully qualified)
 role           : must be "operation", "getter", or "setter
 targetObject   : object on which to execute this method
 targetType     : type of object reference for targetObject.