Java EJB3 持久化注解详解

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"EJB 3持久化" EJB（Enterprise JavaBeans）3是Java企业级应用中的一个核心组件，主要用于创建可复用、分布式的服务器端业务逻辑。EJB 3引入了重大改进，简化了开发流程，其中一个重要变化就是引入了注解（Annotation）来替代XML配置，使得代码更加简洁易读。在EJB 3中，持久化（Persistence）功能是通过Java Persistence API (JPA) 实现的，它允许开发者将对象与数据库表进行映射，实现了对象关系映射（ORM）。JPA 2.0是EJB 3的一个重要组成部分，提供了更多的特性和改进。 1. **@Entity**：这个注解用于标记一个Java类作为实体类，表示该类的对象可以被持久化到数据库中。实体类通常对应于数据库中的一个表。 2. **@Id**：标识一个字段作为主键，用于唯一标识实体。在没有指定的情况下，JPA会尝试找到一个名为"id"的字段作为主键。如果需要自动生成主键，可以结合`@GeneratedValue`注解使用。 3. **@Column**：此注解用于定义实体类的属性如何映射到数据库表的列上。可以设置列的名称、长度、是否可为空等属性。 4. **@Table**：这个注解用于指定实体类对应的数据库表名。如果没有提供，JPA会默认使用实体类的名称。 5. **JavaPersistence2.0ExpertGroup** 和 **JSR-317**：这些指的是JPA 2.0规范的制定者和相关的Java Specification Request（JSR）。JSR-317是JPA 2.0的代号，由Linda De Michiel领导的专家小组负责制定。 6. **ProposedFinalDraft**：这是JPA 2.0规范的一个阶段，表明文档已经进入了最终草案阶段，即将成为官方标准。 7. **Sun Microsystems**：在当时（2009年）是JPA规范的主要贡献者和推动者，现在已经被Oracle公司收购。 8. **版权和许可**：文档中提到的版权信息，说明了规范的使用权限，通常允许在遵循特定条款下使用和复制，但不能未经许可进行商业利用。 EJB 3的持久化通过注解使得开发者无需编写大量的XML配置文件，提高了开发效率。同时，JPA 2.0增加了如级联操作、多对多关联、查询语言JPA QL（Java Persistence Query Language）等特性，进一步提升了开发者的生产力。在实际项目中，开发者可以利用这些工具和概念来设计和实现复杂的企业级数据存储和检索逻辑。

Java Persistence 2.0, Proposed Final Draft

3/13/09 16

Sun Microsystems, Inc.

Java Persistence 2.0, Proposed Final Draft

17 3/13/09

Sun Microsystems, Inc.

List of Tables

Table 1 Definition of the AND Operator ...........................................................................................................155

Table 2 Definition of the OR Operator ..............................................................................................................155

Table 3 Definition of the NOT Operator............................................................................................................155

Table 4 Access Annotation Elements.................................................................................................................320

Table 5 AssociationOverride Annotation Elements...........................................................................................321

Table 6 AssociationOverrides Annotation Elements .........................................................................................323

Table 7 AttributeOverride Annotation Elements ...............................................................................................324

Table 8 AttributeOverrides Annotation Elements..............................................................................................326

Table 9 Basic Annotation Elements ...................................................................................................................328

Table 10 Cacheable Annotation Elements ...........................................................................................................328

Table 11 CollectionTable Annotation Elements ..................................................................................................329

Table 12 Column Annotation Elements ...............................................................................................................331

Table 13 DiscriminatorColumn Annotation Elements.........................................................................................333

Table 14 DiscriminatorValueAnnotation Elements..............................................................................................334

Table 15 ElementCollection Annotation Elements ..............................................................................................335

Table 16 Enumerated Annotation Elements.........................................................................................................338

Table 17 GeneratedValue Annotation Elements ..................................................................................................339

Table 18 IdClass Annotation Elements ................................................................................................................341

Table 19 Inheritance Annotation Elements ..........................................................................................................342

Table 20 JoinColumn Annotation Elements ........................................................................................................343

Table 21 JoinColumns Annotation Elements.......................................................................................................345

Table 22 JoinTable Annotation Elements ............................................................................................................346

Table 23 ManyToMany Annotation Elements .....................................................................................................348

Table 24 ManyToOne Annotation Elements........................................................................................................351

Table 25 MapKey Annotation Elements..............................................................................................................352

Table 26 MapKeyClass Annotation Elements .....................................................................................................353

Table 27 MapKeyColumn Annotation Elements .................................................................................................355

Table 28 MapKeyEnumerated Annotation Elements...........................................................................................357

Table 29 MapKeyJoinColumn Annotation Elements ..........................................................................................358

Table 30 MapKeyJoinColumns Annotation Elements.........................................................................................360

Table 31 MapKeyTemporal Annotation Elements...............................................................................................361

Table 32 MappedBy IdAnnotation Elements.......................................................................................................361

Table 33 OneToMany Annotation Elements........................................................................................................363

Table 34 OneToOne Annotation Elements ..........................................................................................................366

Table 35 OrderBy Annotation Elements ..............................................................................................................368

Table 36 OrderColumn Annotation Elements......................................................................................................370

Table 37 PrimaryKeyJoinColumn Annotation Elements.....................................................................................372

Table 38 PrimaryKeyJoinColumns Annotation Elements ...................................................................................373

Table 39 SecondaryTable Annotation Elements ..................................................................................................375

Table 40 SecondaryTables Annotation Elements.................................................................................................376

Table 41 SequenceGenerator Annotation Elements.............................................................................................377

19 3/13/09

Java Persistence 2.0, Proposed Final Draft

Sun Microsystems, Inc.

Chapter 1 Introduction

This document is the specification of the Java API for the management of persistence and object/rela-

tional mapping with Java EE and Java SE. The technical objective of this work is to provide an

object/relational mapping facility for the Java application developer using a Java domain model to man-

age a relational database.

This is the Proposed Final Draft of the Java Persistence 2.0 specification. This draft

addresses improvements in the areas of domain modeling, O/R mapping, EntityManager

and Query interfaces, and the Java Persistence query language. It adds an API for criteria

queries, a metamodel API, and support for validation.

We welcome feedback from the community on the features in this draft.

1.1 Expert Group

This work is being conducted as part of JSR 317 under the Java Community Process Program. This

specification is the result of the collaborative work of the past and present members of the JSR 317

Expert Group: Adobe Systems Inc.: Jeff Vroom; akquinet tech@Spree: Michael Bouschen; BEA Sys-

tems: Patrick Linskey; DataDirect: Eric Samson; Ericsson AB: Erik Brakkee; IBM: Kevin Sutter, Pinaki

Poddar; Inria: Florent Benoit; Oracle: Michael Keith, Gordon Yorke; Pramati Technologies: Deepak

Anupalli; Red Hat Middleware LLC: Gavin King, Emmanuel Bernard; SAP AG: Rainer Schweigkoffer,

Adrian Goerler; SpringSource Inc.: Matthew Adams; Sun Microsystems: Linda DeMichiel (Specifica-

tion Lead), Kenneth Saks; Sybase: Evan Ireland; Tmax Soft Inc.: Wonseok Kim; Adam Bien; Antonio

Goncalves; Chris Maki.

1.2 Document Conventions

The regular Times font is used for information that is prescriptive by this specification.

The italic Times font is used for paragraphs that contain descriptive information, such as notes describ-

ing typical use, or notes clarifying the text with prescriptive specification.

The Courier font is used for code examples.

The Helvetica font is used to specify the BNF of the Java Persistence query language.

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