<?xml version="1.0"?>
<!DOCTYPE ejb-jar PUBLIC
"-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN"
"http://
java.sun.com/dtd/ejb-jar_2_0.dtd">
<ejb-jar>
<enterprise-beans>
<entity>
<ejb-name>BookCatalog</ejb-name>
<local-home>BookCatalogLocalHome</local-home>
<local>BookCatalogLocal</local>
<ejb-class>BookCatalogBean</ejb-class>
<persistence-type>Container</persistence-type>
<prim-key-class>String</prim-key-class>
<reentrant>False</reentrant>
<cmp-version>2.x</cmp-version>
<abstract-schema-name>BookCatalog</abstract-schema-name>
<cmp-field>
<field-name>title</field-name>
</cmp-field>
<cmp-field>
<field-name>author</field-name>
</cmp-field>
<cmp-field>
<field-name>publisher</field-name>
</cmp-field>
<query>
<query-method>
<method-name>findByTitle</method-name>
<method-params>
<method-param>
java.lang.String</method-param>
</method-params>
</query-method>
<ejb-ql>
<![CDATA[SELECT DISTINCT OBJECT(obj) FROM BookCatalog obj WHERE obj.title = ?1 ]]>
</ejb-ql>
</query>
</entity>
</enterprise-beans>
<relationships>
<ejb-relation>
<ejb-relation-name>BookCatalog-Editions</ejb-relation-name>
<ejb-relationship-role>
<ejb-relationship-role-name>
BookCatalog-Has-Editions
</ejb-relationship-role-name>
<multiplicity>One</multiplicity>
<relationship-role-source>
<ejb-name>BookCatalog</ejb-name>
</relationship-role-source>
<cmr-field>
<cmr-field-name>editions</cmr-field-name>
<cmr-field-type>
java.util.Collection</cmr-field-type>
</cmr-field>
</ejb-relationship-role>
<ejb-relationship-role>
<ejb-relationship-role-name>
Editions-Belong-To-BookCatalog
</ejb-relationship-role-name>
<multiplicity>One</multiplicity>
<cascade-delete />
<relationship-role-source>
<ejb-name>Edition</ejb-name>
</relationship-role-source>
</ejb-relationship-role>
</ejb-relation>
</relationships>
</ejb-jar>
相比之下,对应于EJB 2.1实体bean类的EJB 3.0实体Bean类是一个纯旧式Java对象(POJO),并且非常简单(请看例3)。此bean类的EJB 3.0版本使用了元数据注释@Entity,而EJB 2.1部署描述符ejb-jar.xml文件中用元素符指定的查找方法,在EJB 3.0 Bean类中,则使用@NamedQueries和@NamedQuery注释来指定;ejb-jar.xml文件中用元素符指定的CMR关系,在EJB 3.0 Bean类中,则用元数据注释来指定;另外,主要的关键字段通过@Id注释来指定。表1中列出了一些EJB 3.0的元数据注释。
例3:BookCatalogBean.java
import
javax.persistence.Entity;
import
javax.persistence.NamedQuery;
import
javax.persistence.Id;
import
javax.persistence.Column;
import
javax.persistence.OneToMany;
@Entity
@NamedQuery(name="findByTitle", queryString =
"SELECT DISTINCT OBJECT(obj) FROM BookCatalog obj WHERE obj.title = ?1")
public class BookCatalogBean
{
public BookCatalogBean(){}
public BookCatalogBean(String title)
{
this.title=title;
}
private String title;
private String author;
private String publisher;
@Id
@Column(name="title", primaryKey="true")
public String getTitle(){return title;}
public void setTitle(){this.title=title;}
public void setAuthor(String author){this.author=author;}
public String getAuthor(){return author;}
public void setPublisher(String publisher)
{
this.publisher=publisher;
}
public String getPublisher(){return publisher;}
private
java.util.Collection<Edition>editions;
@OneToMany
public void setEditions(
java.util.Collection editions)
{
this.editions=editions;
}
public
java.util.Collection getEditions(){return editions;}
}