老板需要的员工：早上起床三点半中午可以不吃饭晚上干到看不见天天都能连轴转工人需要的工作：早上上班八点半中午回家去吃饭晚上要把电视看周末休闲公园转
在前面的例子中，我们演示了一对多和多对一的例子，在本章将演示多对多和一对一的关系。 学生和老师就是多对多的关系。一个学生有多个老师，一个老师教多个学生。 学生和档案就是一对一的关系（不知道国外的学生有没有档案？）。 为了实现多对多的关系，数据库中需要关联表，用以在两个实体间建立关联。JBoss可以自动生成关联表，你也可以@AssociationTable来指定关联表的信息。 如: @ManyToMany(cascade = {CascadeType.CREATE, CascadeType.MERGE}, fetch = FetchType.EAGER, isInverse = true) @AssociationTable(table = @Table(name = "STUDENT_TEACHER"), joinColumns = {@JoinColumn(name = "TEACHER_ID")},inverseJoinColumns = {@JoinColumn(name = "STUDENT_ID")}) @ AssociationTable的注释声明如下：
@Target({METHOD, FIELD}) public @interface AssociationTable {
Table table() default @Table(specified=false);
JoinColumn[] joinColumns() default {};
JoinColumn[] inverseJoinColumns() default {};
} 关联表注释指定了关联表的名称、主表的列和从表的列。 为了实现一对一的关系，需要用@OneToOne来注释。 如: @OneToOne(cascade = {CascadeType.ALL})
@JoinColumn(name = "DOSSIER_ID") public Dossier getDossier()
{
return dossier;
} 这定义了一个单向的一对一的关系。如果在Dossier也定义了相关的关联，那么它就是双向的。双向的意思就是通过一个Student实体就可以查找到一个Dossier，通过一个Dossier就可以查找到一个Student。 @ OneToOne的注释声明如下：
@Target({METHOD, FIELD}) @Retention(RUNTIME) public @interface OneToOne {
String targetEntity() default "";
CascadeType[] cascade() default {};
FetchType fetch() default EAGER;
boolean optional() default true;
} 这个例子主要有以下几个文件，这个例子主要实现了学生和老师、学生和档案之间的关系。Student、Teacher、Dossier都是实体Bean。Student和Dossier是一个双向的OneToOne之间的关系，Student和Teacher是ManyToMany的关系，也是双向的。和前面的例子一样，我们还是使用Client测试。 Student.java：实体Bean。 Dossier.java：实体Bean所依赖的类。 Teacher.java：实体Bean所依赖的类。 EntityTest.java：会话Bean的业务接口 EntityTest Bean.java：会话Bean的实现类 Client.java：测试EJB的客户端类。 jndi.properties：jndi属性文件，提供访问jdni的基本配置属性。 Build.xml：ant 配置文件，用以编译、发布、测试、清除EJB。 下面针对每个文件的内容做一个介绍。 Student.java package com.kuaff.ejb3.relationships;
import javax.ejb.CascadeType;
import javax.ejb.Entity;
import javax.ejb.FetchType;
import javax.ejb.GeneratorType;
import javax.ejb.Id;
import javax.ejb.JoinColumn;
import javax.ejb.OneToOne;
import javax.ejb.ManyToMany;
import javax.ejb.Table;
import javax.ejb.AssociationTable;
import java.util.ArrayList;
import java.util.Set;
import java.util.Collection;
import java.io.Serializable; @Entity @Table(name = "STUDENT") public class Student implements Serializable {
private int id;
private String first;
private String last;
private Dossier dossier;
private Set
{
return id;
} public void setId(int id)
{
this.id = id;
} public void setFirst(String first)
{
this.first = first;
} public String getFirst()
{
return first;
} public void setLast(String last)
{
this.last = last;
} public String getLast()
{
return last;
} public void setDossier(Dossier dossier)
{
this.dossier = dossier;
} @OneToOne(cascade = {CascadeType.ALL})
@JoinColumn(name = "DOSSIER_ID") public Dossier getDossier()
{
return dossier;
} public void setTeacher(Set
{
this.teachers = teachers;
} @ManyToMany(cascade = {CascadeType.CREATE, CascadeType.MERGE}, fetch = FetchType.EAGER, isInverse = true)
@AssociationTable(table = @Table(name = "STUDENT_TEACHER"), joinColumns = {@JoinColumn(name = "TEACHER_ID")},inverseJoinColumns = {@JoinColumn(name = "STUDENT_ID")}) public Set
{
return teachers;
}
} Dossier.java package com.kuaff.ejb3.relationships; import javax.ejb.Entity;
import javax.ejb.GeneratorType;
import javax.ejb.Id; @Entity public class Dossier implements java.io.Serializable
{
private Long id;
private String resume; @Id(generate = GeneratorType.AUTO)
public Long getId()
{
return id;
} public void setId(Long id)
{
this.id = id;
} public void setResume(String resume)
{
this.resume = resume;
} public String getResume()
{
return resume;
}
} Teacher.java package com.kuaff.ejb3.relationships; import javax.ejb.AssociationTable;
import javax.ejb.Basic;
import javax.ejb.CascadeType;
import javax.ejb.Column;
import javax.ejb.Entity;
import javax.ejb.FetchType;
import javax.ejb.Id;
import javax.ejb.JoinColumn;
import javax.ejb.ManyToMany;
import javax.ejb.Table;
import javax.ejb.Transient;
import javax.ejb.Version;
import java.util.Set;
import javax.ejb.GeneratorType; @Entity public class Teacher implements java.io.Serializable
{
private Long id;
private String resume;
private String name;
private String info;
private Set
{
return id;
} public void setId(Long id)
{
this.id = id;
} public void setName(String name)
{
this.name = name;
} public String getName()
{
return name;
} public void setInfo(String info)
{
this.info = info;
} public String getInfo()
{
return info;
} public void setStudents(Set
{
this.students = students;
} @ManyToMany(cascade = {CascadeType.CREATE, CascadeType.MERGE}, fetch = FetchType.EAGER)
@AssociationTable(table = @Table(name = "STUDENT_TEACHER"), joinColumns = {@JoinColumn(name = "TEACHER_ID",referencedColumnName="ID")},
inverseJoinColumns = {@JoinColumn(name = "STUDENT_ID",referencedColumnName="ID")}) public Set
{
return students;
}
} EntityTest.java package com.kuaff.ejb3.relationships; import javax.ejb.Remote;
import java.util.List; @Remote public interface EntityTest
{
public void createData();
public List findByName(String name);
} EntityTestBean.java
package com.kuaff.ejb3.relationships; import javax.ejb.EntityManager;
import javax.ejb.Inject;
import javax.ejb.Stateless;
import java.util.HashSet;
import java.util.Set;
import java.util.List; @Stateless public class EntityTestBean implements EntityTest
{
private @Inject EntityManager manager;
public void createData()
{
Teacher teacher1 = new Teacher();
Teacher teacher2 = new Teacher(); Set
Set
Student student1 = new Student();
Student student2 = new Student();
Student student3 = new Student(); Dossier dossier1 = new Dossier();
Dossier dossier2 = new Dossier();
Dossier dossier3 = new Dossier();
teacher1.setId(new Long(1));
teacher1.setName("hushisheng");
teacher1.setInfo("胡时胜教授，博士生导师");
manager.create(teacher1);
teacher2.setId(new Long(2));
teacher2.setName("liyongchi");
teacher2.setInfo("李永池教授，博士生导师");
manager.create(teacher2); student1.setFirst("晁");
student1.setLast("岳攀");
dossier1.setResume("这是晁岳攀的档案");
student1.setDossier(dossier1);
students1.add(student1); student2.setFirst("赵");
student2.setLast("志伟");
dossier2.setResume("这是赵志伟的档案");
student2.setDossier(dossier2);
students1.add(student2); student3.setFirst("田");
student3.setLast("明"); dossier3.setResume("这是田明的档案");
student3.setDossier(dossier3);
students2.add(student3); teacher1.setStudents(students1);
teacher2.setStudents(students2); } public List findByName(String name)
{
return manager.createQuery("from Teacher t where t.name = :name").setParameter("name", name).listResults();
} } 在这个会话Bean中提供了创建各个实体Bean的方法，并提供了查找老师的方法。 Client.java package com.kuaff.ejb3.secondary; import javax.naming.InitialContext;
import javax.naming.NamingException;
import java.util.List; public class Client
{
public static void main(String[] args) throws NamingException
{
InitialContext ctx = new InitialContext();
StudentDAO dao = (StudentDAO) ctx.lookup(StudentDAO.class.getName());
int id = dao.create("晁","岳攀","8","smallnest@kuaff.com","男");
dao.create("朱","立焕","6","zhuzhu@kuaff.com","女");
List list = dao.findAll();
for(Object o:list)
{
Student s = (Student)o;
System.out.printf("%s%s的性别:%s%n",s.getName().getFirst(),s.getName().getLast(),s.getGender());
dao.evict(s);
}
}
} 这个客户端用来测试。 请运行{$JBOSS_HOME}/bin目录下的run.bat: run –c all,启动JBOSS。 http://localhost:8080/jmx-console/HtmlAdaptor?action=inspectMBean&name=jboss%3Aservice%3DHypersonic%2Cdatabase%3DlocalDB，然后调用startDatabaseManager()方法，打开HSQL管理工具管理数据库。 在Eclipse的Ant视图中执行ejbjar target。或者在命令行下，进入到此工程目录下，执行ant ejbjar,将编译打包发布此EJB。 在Eclipse的Ant视图中执行run target。或者在命令行下，进入到此工程目录下，执行ant run,测试这个EJB。
本文EJB3.0开发之多对多和一对一到此结束。明天是世上增值最快的一块土地，因它充满了希望。小编再次感谢大家对我们的支持！
