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Important MBean Metadata classes are described below:
MBeanInfo class:
This class is used to fully describe an MBean: its attributes,
operations, constructors, and the notification types it can
send. It describes the MBean's overall purpose or functionality.
MBeanFeatureinfo class:
This class is the parent of all the other component metadata
classes. It contains two methods getName() and getDescription()
which return the name and a readable string description of the
component.
MBeanAttributeInfo class:
The MBeanAttributeInfo class describes an attribute in the
MBean's management interface. An attribute is characterized by
its type and how it is accessed. This type of an attribute is
the Java class that is used to represent it when calling its
getter or setter methods. The getType() method returns a string
containing the fully qualified name of this class.
MBeanOperationInfo class:
The MBeanOperationInfo class describes an individual operation
of an MBean. An operation is defined by its signature, return
type, and its impact.
MBeanParameterInfo class:
The MBeanParameterInfo class is used to describe a parameter of
an operation or a constructor.
MBeanNotificationInfo class:
The MBeanNotificationInfo class is used to describe the
notifications that are sent by an MBean. The getNotifTypes
method returns an array of strings containing the notification
types that the MBean can emit.
Agent Layer:
A JMX agent is a management entity that runs in a Java Virtual Machine (JVM) and acts as the bridge between the MBeans and the management application. A JMX
agent is composed of an MBean server, a set of MBeans representing managed
resources, a minimum number of agent services implemented as MBeans, and typically
at least one protocol adaptor or connector.
The key components in the JMX agent architecture can be further defined as follows:
The MBean server and Agent services can either be components defined in this specification or services developed by third parties.
The agent service MBeans defined by the JMX specification further provide dynamic loading services that allow the agent to instantiate MBeans using Java classes and native libraries dynamically downloaded from the network. These include monitoring capabilities for attribute values in MBeans, a timer service that can send notifications at predetermined intervals and act as a scheduler, and a relation service that defines associations between MBeans and maintains the consistency of the relation
MBean Server:
The Managed Bean server, or MBean server is the core component of the Java Management Extensions (JMX) agent infrastructure. The MBean server is a registry for MBeans in the agent. The MBean server is the component that provides the services for manipulating MBeans. All management operations performed on the MBeans are done through the MBeanServer interface.
In general the MBean server registers MBeans that represent resources used for management purposes or Mbeans that add management functionality to the agent.
Some components of the infrastructure, such as the connector clients and protocol
adaptors, can be implemented as MBeans. This allows such components to benefit
from the dynamic management infrastructure.
A JMX agent has a factory class for finding or creating an MBean server through the
factory's static methods. This allows more flexible agent applications and possibly
more than one MBean server in an agent.
MBeans can be registered either by the agent application, or by other MBeans. The interface of the MBeanServer class allows two different kinds of registration. The first one is the instantiation of a new MBean and registration of this MBean in a single operation. The second is the registration of an already existing MBean instance.
Agent Services:
Advanced Dynamic Loading:
Dynamic loading is usually performed by the management applet (m-let) service
that is used to instantiate MBeans. These MBeans are obtained from a remote URL on the network.
The Java Management Extensions (JMX) specification also defines lower-level
mechanisms for class loading. These allow developers to extend the functionality of
the m-let service or to load classes without it.
The m-let service allows you to instantiate and register one or more MBeans from a
remote URL, in the MBean server. The m-let service does this by loading an m-let
text file, that specifies information on the MBeans to be obtained. The information on
each MBean is specified in a tag similar to those used in XML, called the MLET tag.
The location of the m-let text file is specified by a URL. When an m-let text file is
loaded, all classes specified in MLET tags are downloaded, and an instance of each
MBean specified in the file is created and registered.
The m-let service is itself implemented as an MBean and registered in the MBean
server. This way it can be used by other MBeans, by the agent application, or by remote
management applications.
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