"Java JDK 12管理扩展指南：Release 12F13901-01"

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The JDK12 Java Management Extensions Guide, released in March 2019, provides comprehensive information on the Java Platform, Standard Edition. This guide, with the document number F13901-01, covers all aspects of Java Management Extensions (JMX) in the Release 12 version. The JMX technology in Java allows developers to instrument and manage Java applications. It provides a standard way of managing resources such as applications, devices, and services in a network. With JMX, developers can monitor and manage applications remotely, configure applications, and respond to various notifications. The guide includes detailed information on how to use JMX to build manageable applications, including setting up a JMX environment, creating MBeans (Managed Beans), accessing and manipulating MBeans, and monitoring and managing applications through JMX. It also covers how to use the JMX Remote API to enable remote management of Java applications. Copyrighted by Oracle and its affiliates, the document warns of restrictions on the use and disclosure of the software and related documentation due to intellectual property laws. Users are advised to adhere to the license agreement and the legal regulations governing the use of the content provided in the guide. Overall, the JDK12 Java Management Extensions Guide is a valuable resource for developers looking to leverage JMX technology to build scalable and manageable Java applications. It provides in-depth explanations, code examples, and best practices for implementing JMX in Java applications, empowering developers to efficiently monitor, manage, and troubleshoot their applications in a distributed environment.

Instrumenting Resources by Using MBeans

To manage resources by using JMX technology, you must first instrument the

resources in the Java programming language. You can use Java objects known as

MBeans to implement the access to the instrumentation of resources. MBeans must

follow the design patterns and interfaces defined in the JMX Specification to ensure

that all MBeans provide the instrumentation of managed resources in a standardized

way.

After a resource is instrumented by MBeans, it can be managed through a JMX agent.

MBeans do not require knowledge of the JMX agent with which they operate.

MBeans are designed to be flexible, simple, and easy to implement. Developers of

applications, systems, and networks can make their products manageable in a

standard way without investing in complex management systems. Existing resources

can be made manageable with minimum effort.

In addition, the instrumentation level of JSR 3: Java Management Extensions (JMX)

Specification specifies a notification mechanism that enables MBeans to generate and

propagate notification events to components of the other levels.

Creating a JMX Agent

A JMX agent is a standard management agent that directly controls resources and

makes them available to remote management applications. A JMX agent is usually

located on the same system as the resources that it controls, but this is not a

requirement.

The core component of a JMX agent is the MBean server, a managed object server in

which MBeans are registered. A JMX agent also includes a set of services to manage

MBeans, and at least one communications adaptor or connector to enable access by a

management application.

When you implement a JMX agent, you do not need to know the semantics or

functions of the resources that the agent will be used to manage. In fact, a JMX agent

does not even need to know which resources it will serve, because any resource

instrumented in compliance with the JMX specification can use any JMX agent offering

the services that it requires. In addition, the agent does not need to know the functions

of the management applications that will access it.

Managing Resources Remotely

JMX API instrumentation can be accessed either through existing management

protocols such as the Simple Network Management Protocol (SNMP), or through

proprietary protocols. The MBean server relies on protocol adaptors and connectors to

make a JMX agent accessible from management applications outside the agent’s Java

Virtual Machine (JVM).

Each adaptor provides a view through a specific protocol of all MBeans registered in

the MBean server. For example, an HTML adaptor could display an MBean in a

browser.

Connectors provide a manager-side interface that handles the communication

between the manager and the JMX agent. Each connector provides the same remote

Chapter 2

Instrumenting Resources by Using MBeans

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Instrumenting Your Resources for JMX

Technology

This chapter outlines the concepts behind instrumenting resources for management by

using JMX technology in the following sections:

• Manageable Resources

• Managed Beans (MBeans)

• Java Virtual Machine Instrumentation

Manageable Resources

Different types of resources can be managed using JMX technology, for example an

application, an implementation of a service, a device, or a user. For a given resource

to be managed by JMX technology, it must be developed in the Java language, or at

least offer a Java language wrapper. The resource must also be instrumented by one

or more Java objects known as managed beans (MBeans), in compliance with the

JMX specification.

Developers of applications and devices can choose the granularity of objects that are

instrumented as MBeans. An MBean might represent the smallest object in an

application, or it could represent the entire application. Application components

designed with their management interface in mind can typically be written as MBeans.

MBeans can be used as wrappers for legacy code without a management interface or

as proxies for code with a legacy management interface.

Managed Beans (MBeans)

The Java objects that implement resources and their instrumentation are called

managed beans (MBeans). MBeans must follow the design patterns and interfaces

defined in the JMX Specification (JSR 3) to ensure that all MBeans provide the

instrumentation of managed resources in a standardized way.

The instrumentation of a given resource is provided by one or more MBeans that are

either standard or dynamic. Standard MBeans are Java objects that conform to certain

design patterns derived from the JavaBeansTM component model. Dynamic MBeans

conform to a specific interface that offers more flexibility at runtime. MXBeans

reference only a predefined set of types.

The instrumentation of a resource allows it to be manageable through the agent level

described in Using JMX Agents. MBeans do not require knowledge of the JMX agent

with which they operate.

MBeans are designed to be flexible, simple, and easy to implement. Developers of

applications, services, or devices can make their products manageable in a standard

way without having to understand or invest in complex management systems. Existing

3-1

Using JMX Agents

A Java Management Extensions (JMX) agent is a management entity that runs in a

Java Virtual Machine (JVM) and acts as the liaison between the managed beans

(MBeans) and the management application. The various components of a JMX agent

are outlined in the following sections:

• MBean Server

• Agent Services

• Protocol Adaptors and Connectors

MBean Server

The MBean server is the core component of a JMX agent. It’s a registry for objects in a

JMX agent that are exposed to management operations. An object that is registered

with the MBean server is visible to management applications. The MBean server

exposes only the management interface of an MBean, never its direct object

reference.

Any resource that you want to manage from outside the agent’s JVM must be

registered as an MBean with the server. The MBean server provides a standardized

interface for accessing MBeans within the same JVM, giving local objects all the

benefits of manipulating manageable resources. MBeans can be instantiated and

registered by:

• Another MBean

• The agent itself

• A remote management application

When you register an MBean, you must assign it a unique object name. A

management application uses the object name to identify the object on which it is to

perform a management operation. The operations available on MBeans include:

• Discovering the management interface of MBeans

• Reading and writing their attribute values

• Performing operations defined by the MBeans

• Getting notifications emitted by MBeans

• Querying MBeans by using their object name or their attribute values

Agent Services

Agent services are objects that can perform management operations on the MBeans

that are registered with the MBean server. By including management intelligence into

the agent, JMX helps you build more powerful management solutions. Agent services

can be MBeans as well, allowing them and their functionality to be controlled through

the MBean server. The JMX Specification defines the following agent services:

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