Java消息服务入门指南

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"Java消息服务 (Java Message Service, JMS) 是一种标准API，用于在Java应用程序之间交换异步消息。它提供了一种可靠的消息传递机制，允许应用程序创建、发送、接收和读取消息，而无需直接连接到接收方。JMS在分布式系统中尤其有用，因为它促进了解耦和可扩展性，使得系统组件可以独立工作，即使在高负载或网络故障情况下也能保持通信。" JMS入门: 对于初学者来说，理解JMS的核心概念是至关重要的。首先，JMS中主要有两种消息模型：点对点（Point-to-Point, PTP）和发布/订阅（Publish/Subscribe, Pub/Sub）。在点对点模型中，消息从一个生产者发送到一个队列，然后由一个或多个消费者接收，每个消息只被一个消费者处理。而在发布/订阅模型中，消息被发送到主题，多个订阅者可以接收到相同的消息。 JMS接口与实体: JMS定义了几个关键接口和实体，包括： 1. **Message**: 这是JMS的核心对象，包含消息数据和元数据，如目的地、优先级等。 2. **MessageProducer** 和 **MessageConsumer**: 分别用于发送和接收消息。 3. **Queue** 和 **Topic**: 代表点对点和发布/订阅模型中的目的地。 4. **ConnectionFactory**: 它是创建连接的工厂，连接到JMS提供者（例如ActiveMQ、IBM WebSphere MQ等）。 5. **Connection**: 表示到JMS提供者的网络连接，可以通过该连接创建会话（Session）。 6. **Session**: 是线程安全的工作单元，用于创建消息生产者、消费者以及进行消息事务管理。消息类型: JMS支持多种消息类型，包括： - **TextMessage**: 包含纯文本数据。 - **ObjectMessage**: 可以封装任何Java对象，前提是该对象序列化兼容。 - **BytesMessage**: 用于传输二进制数据。 - **MapMessage**: 类似于Java Map，键值对存储数据。 - **StreamMessage**: 用于传输连续的数据流。 JMS事务管理: JMS允许在会话级别上进行事务处理，这意味着一组消息可以作为一个原子操作提交或回滚。这提供了可靠的消息传递，确保消息要么全部被处理，要么全部不被处理。持久性与可靠性: JMS提供持久性消息，即使在发送方或接收方应用程序关闭时，消息也不会丢失。持久性的实现依赖于JMS提供者，但通常通过将消息存储在磁盘上来实现。 JNDI与JMS: Java Naming and Directory Interface (JNDI) 用于查找JMS资源，如ConnectionFactory和目的地。通过JNDI，应用程序可以在运行时动态查找和绑定到JMS资源。 JMS在企业应用中的角色: 在大型企业级系统中，JMS常用于微服务架构、事件驱动架构和工作流系统，作为组件间通信的桥梁，实现解耦、容错和负载均衡。总结: Java消息服务（JMS）是Java开发者用来构建高可用、松耦合系统的强大工具。了解其基本概念、接口、消息类型以及事务管理，可以帮助初学者有效地利用JMS实现可靠和灵活的异步通信。结合实际的JMS提供者和应用场景，开发者可以构建出高效、稳定的企业级应用。

With the exception of the Chat application found in Chapter 2, all of the sample code

has been changed to reflect more up-to-date messaging use cases and to illustrate some

additional features of JMS that were not included in the first edition.

I added several new chapters that were not included in the first edition, for obvious

reasons. You will find new sections in the first chapter on the JMS API, updated

messaging use cases, and a discussion of how messaging has changed how we design

systems. You will also find new chapters on message filtering, Java EE and message-

driven beans, Spring JMS and message-driven POJOs, and messaging design.

In addition to adding new chapters, I significantly revised the existing chapters. Because

I updated the sample code used to illustrate various points throughout the book, I was

in turn forced to rewrite much of the corresponding text. This provided me with the

opportunity to add additional sections and topics, particularly in Chapter 4, Point-to-

Point Messaging, and Chapter 5, Publish-and-Subscribe Messaging. I also reversed these

chapters from the first edition with the belief that it is easier to jump into messaging

with the point-to-point messaging model using queues rather than the publish-and-

subscribe messaging model using topics and subscribers.

I hope you find the new edition of this book helpful in terms of understanding the Java

Message Service and messaging in general.

—Mark Richards

Who Should Read This Book?

This book explains and demonstrates the fundamentals of Java Message Service. It

provides a straightforward, no-nonsense explanation of the underlying technology,

Java classes and interfaces, programming models, and various implementations of the

JMS specification.

Although this book focuses on the fundamentals, it’s no “dummy’s” book. While the

JMS API is easy to learn, the API abstracts fairly complex enterprise technology. Before

reading this book, you should be fluent with the Java language and have some practical

experience developing business solutions. Experience with messaging systems is not

required, but you must have a working knowledge of the Java language.

Organization

The book is organized into 11 chapters and 4 appendixes. Chapter 1 explains messaging

systems, messaging use cases, centralized and distributed architectures, and why JMS

is important. Chapters 2 through 6 go into detail about developing JMS clients using

the two messaging models, point-to-point and publish-and-subscribe, including how

to filter messages using message selectors. Chapters 7 and 10 should be considered

“advanced topics,” covering deployment and administration of messaging systems.

Chapter 8 provides an overview of the Java 2, Enterprise Edition (Java EE) with regard

xiv | Preface

to JMS, including coverage of message-driven beans as part of the Enterprise JavaBeans

3.0 specification. Chapter 9 covers the Spring Framework as it relates to messaging.

Finally, Chapter 11 provides some insight into many of the design considerations and

anti-patterns associated with messaging.

Chapter 1, Messaging Basics

Defines enterprise messaging and common architectures used by messaging ven-

dors. JMS is defined and explained, as are its two programming models, publish-

and-subscribe and point-to-point. Many of the use cases and real-world scenarios

for messaging are described in this chapter, as are the basics of the JMS API.

Chapter 2, Developing a Simple Example

Walks the reader through the development of a simple publish-and-subscribe JMS

client.

Chapter 3, Anatomy of a JMS Message

Provides a detailed examination of the JMS message, the most important part of

the JMS API.

Chapter 4, Point-to-Point Messaging

Examines the point-to-point messaging model through the development of a sim-

ple borrower and lender JMS application. Also covers some of the finer points of

the point-to-point messaging model, including message correlation, dynamic

queues, load balancing, and queue browsing.

Chapter 5, Publish-and-Subscribe Messaging

Examines the publish-and-subscribe messaging model through the enhancement

of the borrower and lender application developed in Chapter 4. This chapter also

covers durable subscribers, nondurable subscribers, dynamic durable subscribers,

and temporary topics.

Chapter 6, Message Filtering

Provides a detailed explanation of message filtering using message selectors.

Chapter 7, Guaranteed Messaging and Transactions

Provides an in-depth explanation of advanced topics, including guaranteed mes-

saging, transactions, acknowledgments, message grouping, and failures.

Chapter 8, Java EE and Message-Driven Beans

Provides an overview of the Java 2, Enterprise Edition (Java EE) version 3.0 with

regard to JMS and includes coverage of message-driven beans (MDBs).

Chapter 9, Spring and JMS

Provides a detailed explanation of the Spring Framework with regards to JMS,

including the Spring JMS Template and message-driven POJOs (MDPs).

Chapter 10, Deployment Considerations

Provides an in-depth examination of features and issues that should be considered

when choosing vendors and deploying JMS applications.

Preface | xv

Chapter 11, Messaging Design Considerations

Provides insight into and explanation of several design considerations, including

the use of internal versus external destinations, request/reply processing, and a

discussion of some of the more common messaging anti-patterns.

Appendix A, The Java Message Service API

Provides a quick reference to the classes and interfaces defined in the JMS package.

Appendix B, Message Headers

Provides detailed information about message headers.

Appendix C, Message Properties

Provides detailed information about message properties.

Appendix D, Installing and Configuring ActiveMQ

Provides detailed information about installing and configuring ActiveMQ to run

the examples in this book.

Software and Versions

This book covers Java Message Service version 1.1. It uses Java language features from

the Java 6 platform. Because the focus of this book is to develop vendor-independent

JMS clients and applications, I have stayed away from proprietary extensions and

vendor-dependent idioms. Any JMS-compliant provider can be used with this book;

you should be familiar with that provider’s specific installation, deployment, and run-

time management procedures to work with the examples. To find out the details of

installing and running JMS clients for a specific JMS provider, consult your JMS ven-

dor’s documentation; these details aren’t covered by the JMS specification. We have

provided the details for running the examples with ActiveMQ, a popular open source

JMS provider, in Appendix D.

The source code examples and explanation in Chapter 8 refer to the Enterprise Java-

Beans 3.0 (EJB 3) specification. The source code examples and explanation in Chap-

ter 9 refer to version 2.5 of the Spring Framework

The examples developed in this book are available through the book’s catalog page at

http://oreilly.com/catalog/9780596522049/examples. These examples are organized by

chapter. Special source code modified for specific vendors is also provided. These

vendor-specific examples include a readme.txt file that points to documentation for

downloading and installing the JMS provider, as well as specific instructions for setting

up the provider for each example.

Conventions Used in This Book

The following typographical conventions are used in this book:

xvi | Preface

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