Java Management Extensions：企业应用管理新范式

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"Java Management Extensions (JMX) 是一种用于管理网络、设备和应用程序的Java技术，当前遵循的规范版本为1.1。本书《Java Management Extensions》由J. Steven Perry撰写，是O'Reilly出版社于2002年出版的一本实践指南，详细介绍了JMX API的使用和JMX架构，包括乐器化层和代理层，并提供了大量实施管理扩展的实例。书中还包含了关于JMX的高级信息，以帮助技术经理和架构师评估各种应用管理方法并考虑采用JMX。" Java Management Extensions (JMX) 是Java平台上的一个核心特性，它提供了一种标准的方式来管理和监控运行中的Java应用程序。JMX允许开发者创建可管理和可监控的组件，这些组件称为Managed Beans（MBeans），它们可以代表系统中的任何资源或服务。JMX的核心概念包括： 1. **MBeans**: MBeans是JMX的核心组件，它们是Java对象，负责暴露管理接口。根据其功能，MBeans可以分为三种类型：Standard MBeans、Dynamic MBeans和Open MBeans。MBeans可以提供状态信息、执行操作和接收通知。 2. **JMX Architecture**: JMX架构包括三个主要部分：管理器（Manager）、代理（Agent）和管理客户端（Management Client）。管理器通过代理与被管理的目标系统交互，代理可以本地运行（如JVM内部）或远程运行。管理客户端则通过JMX API与管理器通信，获取信息或执行管理操作。 3. **Instrumentation Level**: 这是指在应用程序中添加必要的代码以便让JMX能够管理的过程。开发者可以通过实现特定的接口或者使用工具自动将类转化为MBeans来进行仪器化。 4. **Agent Level**: JMX代理是连接管理器和被管理目标之间的桥梁。它负责注册和管理MBeans，处理安全管理，并提供与管理客户端交互的接口。代理可以是内置的（如JVM的一部分）或独立的。 5. **Real-World Examples**: 书中的例子涵盖了如何创建和注册MBeans，如何执行管理操作，以及如何利用JMX进行故障诊断和性能监控。这些实例有助于读者理解和掌握实际开发中的JMX应用。 6. **High-Level Information**: 针对技术决策者和架构师，书中还涵盖了JMX在更广阔的应用场景中的作用，帮助他们理解JMX如何与其他管理框架相比较，以及何时选择JMX作为解决方案。通过《Java Management Extensions》，读者不仅可以深入理解JMX的原理，还能学习到如何在实际项目中有效利用JMX进行系统管理和监控，从而提升应用程序的可靠性和可维护性。无论是开发人员还是运维人员，这本书都提供了丰富的学习资料和实践经验。

The features of a resource that is instrumented as a model MBean are described through

the use of metadata classes that are specific to model MBeans. In addition, every model

MBean must implement the ModelMBean interface, which is defined in Example 1-4.

Example 1-4. The ModelMBean interface

public interface ModelMBean

extends DynamicMBean,

PersistentMBean,

ModelMBeanNotificationBroadcaster {

public void setModelMBeanInfo(ModelMBeanInfo inModelMBeanInfo)

throws MBeanException, RuntimeOperationsException;

public void setManagedResource(Object mr, String mr_type)

throws MBeanException,

RuntimeOperationsException,

InstanceNotFoundException,

InvalidTargetObjectTypeException;

}

Notice that the ModelMBean interface extends the DynamicMBean interface, which means

that a model MBean is a dynamic MBean. However, every JMX implementation is

required to ship an off-the-shelf implementation of

ModelMBean called

RequiredModelMBean. This presents the developer with a key benefit: because a model

MBean implementation already exists, the work of writing one is already done. While the

instrumentation developer must still create the necessary metadata classes (which we will

discuss shortly), she does not have to implement the

ModelMBean interface, which

significantly reduces development time.

Model MBeans introduce the concept of a descriptor, which is an additional set of

metadata—specific to model MBeans—that allows the instrumentation developer to

provide a much richer description of any MBean feature. Certain predefined descriptor

values provide support for functionality such as the following:

• Automatic attribute change notifications

• Persistence of the MBean's state at a specified interval

• Logging of MBean state changes

• Caching of an MBean feature (such as an attribute value or the return value of an

operation) to improve performance for static (or relatively static) MBean features

Model MBean metadata extends dynamic MBean metadata, in that each model MBean

metadata class extends its dynamic MBean counterpart. This relationship is shown in

Figure 1-3

Figure 1-3. Model MBean metadata classes

Using the standard, dynamic, or model MBean instrumentation approaches allows us to

describe MBean features (i.e., attributes, constructors, parameters, operations, and

notifications) that are one of the following types:

• A fundamental Java type, such as boolean, char, long, or float (through its

corresponding JDK wrapper—Boolean, Char, Long, or Float, respectively)

• A string, as java.lang.String

• An array of fundamental types or strings

However, sometimes MBean attributes are more complex. Open MBeans were designed

in an effort to make MBeans accessible to the widest possible range of management

applications. Strictly speaking, you can use complex types on the management interface

of standard, dynamic, and model MBeans. However, for a management application to

correctly interpret the state of those types, the classes (i.e., the Java bytecode)

representing those types must be available to the management application. The result is a

coupling between the management application and the resources it manages,

compromising the maintainability of the underlying managed resources. Open MBeans

eliminate the need for management applications to understand the classes describing the

complex types, deferring this intelligence instead to a predefined set of open MBean

classes that can universally describe those types.

Every open MBean type is a concrete subclass of an abstract open MBean class called

OpenType, and only subclasses of OpenType are allowed to describe features of open

MBeans. Three new types are defined that allow the instrumentation developer to

describe MBean features of arbitrary complexity:

ArrayType

Describes an n-dimensional array of any open MBean type

CompositeType

Describes an arbitrarily complex structure of open MBean types

TabularType

Describes a tabular structure (analogous to a database table) of any number of

rows, where the same

CompositeType describes each row in the table

At some point, the state of an MBean (or any object, for that matter) must be resolved

down to fundamental types, strings, or arrays. However, open MBeans provide us with a

mechanism to describe complex links between types so that those links can be resolved

indirectly. For example, if we want to instrument a class

A as an MBean, and A in turn

contains an instance of a class B, which contains an instance of a class C, we need some

way to describe the links in the inheritance graph between A, B, and C. It is for precisely

this sort of arbitrary complexity that open MBeans were designed.

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