EJB3.0早期草案：企业JavaBean 3.0规范详解

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EJB3.0专家小组由Linda De Michiel担任Sun Microsystems的 Specification Lead，该文档是EJB3.0规范的早期草案，发布于2004年6月24日。这个版本的Enterprise JavaBeans (EJB) 3.0规格旨在提供对EJB 3.0体系结构和使用的深入理解，它是Java Server Faces (JSR-220) 规范的一部分。 EJB 3.0相较于之前的版本有显著改进，重点在于简化开发过程，减少样板代码，并提高性能。该规范强调了组件模型（Component Model）的灵活性，允许开发者使用更多的面向切面编程(AOP)和依赖注入(DI)技术。早期草案的发布标志着一个重要的里程碑，预示着企业级Java应用开发进入了更高效、模块化的新时代。在EJB 3.0中，企业应用程序部署单元(EAR)的定义得到了扩展，使得EAR可以包含更丰富的组件类型，如Session Beans（用于处理会话相关的业务逻辑）、Message-driven Beans（MDBs，处理异步消息）和Entity Beans（用于持久化数据）。此外，该规范还提倡使用JPA（Java Persistence API）作为默认的ORM框架，以便更好地管理和操作数据库。 EJB 3.0早期草案也关注了安全性，包括对JACC（Java Authorization Contract for Containers）的支持，以及对Web服务集成的增强。同时，它还引入了容器管理的事务(CMT)模型，降低了开发者对手动管理事务的需求。值得注意的是，这个文档是早期版本，意味着可能存在未完成或待完善的特性，且版权方面受到保护，未经Sun Microsystems及其许可方的书面授权，不得复制或使用部分内容。任何使用EJB 3.0规范的信息都必须遵守协议条款。 EJB 3.0规范的早期草案为Java开发者提供了一个基础，指导他们在构建可伸缩、高性能的企业级应用时如何利用EJB 3.0的技术革新。随着技术的发展，正式版的EJB 3.0规范可能会包含更多实用的功能和优化，适应不断变化的市场需求。

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Requirements for Stateless Session Beans Enterprise JavaBeans 3.0, Early Draft Stateless Session Beans

15 June 24, 2004 10:45 am

Sun Microsystems Inc

Chapter 3 Stateless Session Beans

This chapter describes requirements that are speciﬁc to stateless session beans.

3.1 Requirements for Stateless Session Beans

3.1.1 Business Interface

A session bean must have a business interface. This interface may be implemented by the session bean,

or it may be generated.

• In the case of session beans providing a local or remote client view, this interface is typically

an ordinary Java interface (POJI), not an EJBObject or EJBLocalObject interface.

• In the case of a session bean that implements a web service, a web service interface is not

required to be deﬁned as such. The WebMethod annotations are used to identify the methods

that are exposed as web service operations. The session bean that serves as a web service end-

point is annotated with the WebService annotation. These annotations for web services are

deﬁned by JSR-181, with which this speciﬁcation will be aligned as we progress.

Stateless Session Beans Enterprise JavaBeans 3.0, Early Draft Other Requirements

6/24/04 16

Sun Microsystems Inc.

3.1.2 Home Interface

Stateless session beans do not require home interfaces. Under the EJB 3.0 API, home interfaces are typ-

ically not used for stateless session beans.

3.1.3 Bean Class

A stateless session bean must be annotated with the Stateless annotation or must implement the

javax.ejb.SessionBean interface.

A stateless session bean that is annotated with the Stateless annotation may (but is not required to)

implement the setSessionContext method of the javax.ejb.SessionBean interface.

The bean class may optionally implement the ejbCreate and/or ejbRemove method. If it does, the

container will call these methods as required by the EJB 2.1 speciﬁcation.

3.1.4 Dependency Injection

If a stateless session bean uses dependency injection mechanisms for the acquisition of references to

resources or other objects in its environment (see Chapter 8), the container injects these references when

the stateless session bean is transitioned to the “method-ready” state. Injection will occur before any

business methods are invoked on the bean instance and after the setSessionContext method (if

any) is called. (See Section 7.8.1 and Figure 12 of the EJB 2.1 speciﬁcation.)

3.1.5 Client View

The local or remote client of a session bean acquires a reference to a session bean business interface

either through one of the dependency injection or lookup mechanisms described in Chapter 8. Alterna-

tively, the client may use the explicit JNDI lookup mechanisms described by the EJB 2.1 speciﬁcation.

3.2 Other Requirements

The following requirements from the EJB 2.1 speciﬁcation apply to stateless session beans written to

the EJB 3.0 API.

• The requirements of sections 7.11.2 and 7.11.4, except as described above.

• The requirements of Section 7.8.1.

• The requirements of Section 7.8.2, Table 3, and Section 7.8.3, with the following exceptions:

• The getEJBHome, getEJBLocalHome, getEJBObject, and getEJBLo-

calObject methods must not be called. The container must throw the Illegal-

StateException if these methods are called.

• Other requirements (if any) as appropriate TBD.

Stateful Session Beans Enterprise JavaBeans 3.0, Early Draft Requirements for Stateful Session Beans

6/24/04 18

Sun Microsystems Inc.

A stateful session bean that does not implement the javax.ejb.SessionBean interface may selec-

tively implement methods of the SessionBean interface.

A stateful session bean may implement the SessionSynchronization interface, as described in

the EJB 2.1 speciﬁcation, Section 7.5.4.

4.1.4 Dependency Injection

If a stateful session bean uses dependency injection mechanisms for the acquisition of references to

resources or other objects in its environment (see Chapter 8), the container injects these references when

the stateful session bean is transitioned to the “method-ready” state. Injection will occur before any

business methods are invoked on the bean instance and after the setSessionContext method (if

any) is called. See Section 7.6 and Figure 6 of the EJB 2.1 speciﬁcation.

4.1.5 Client View

The local or remote client of a session bean acquires a reference to the session bean business interface

either through one of the dependency injection or lookup mechanisms described in Chapter 8. Alterna-

tively, the client may use the explicit JNDI lookup mechanisms described by the EJB 2.1 speciﬁcation.

When a stateful session bean is looked up or otherwise obtained through the explicit JNDI

lookup mechanisms, the container must provide a new stateful session bean instance, as

required by the J2EE speciﬁcation (Section “Java Naming and Directory Interface (JNDI)

Naming Context”).

When stateful session bean is injected into a client context or is obtained by lookup, the container cre-

ates a new stateful session bean instance to which method invocations from the client are delegated.

This instance, however, is uninitialized from the client’s point of view, since as the client does not call

an explicit “create” method to obtain and initialize the bean.

Using the EJB 3.0 API, the client typically initializes a stateful session bean through business methods

deﬁned as part of by the bean’s interface. For example, the bean may provide one or more “initializa-

tion” methods for this purpose.

[Note to readers] We are discussing whether we need an annotation to specify business methods that perform

such initialization.

4.1.6 Stateful Session Bean Removal

The Remove annotation may be used to annotate a stateful session bean business method. Use of this

annotation will cause the container to remove the stateful session bean instance after the completion

(normal or abnormal) of the annotated method.

[Note to readers] Should it be customizable (via annotation) that abnormal termination not have this removal

effect? See Section 9.1.2.1.

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