Hbernate Annotation多对多映射

Annotation用起来真是太方便了，多对多映射很需要很少的几个注解就可以搞定.
需要的jar包是ejb3-persistence.jar（见附件）

实例:
用户表：user
CREATE TABLE user(
    id                  BIGINT          NOT NULL,
    optimistic          INT,
    userName            VARCHAR(32),
    password            VARCHAR(128),
    PRIMARY KEY (id)
);
角色表
CREATE TABLE role(
    id             BIGINT           NOT NULL,
    optimistic     INT,
    name           VARCHAR(50),
    active         SMALLINT         NOT NULL,
    PRIMARY KEY (id)
);

角色用户关系表

CREATE TABLE roles2users(
    users_fk    BIGINT,
    roles_fk    BIGINT
)
关系表不要映射成实体，也就是说我们的java代码只有2个类，user类和role类。

[b]java代码[/b]
user对象和role对象都继承自同一个父类，父类封装了id和hibernate版本控制的字段还有equals和hashcode方法：


@MappedSuperclass
public class AutoIDEntity implements java.io.Serializable{
    private static final long serialVersionUID = 1L;
    private Long id;
    private Integer optimistic;

    @Id
    @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="SEQ_STORE")
    public Long getId() {
      return this.id;
    }

    @Version
    public Integer getOptimistic() {
      return this.optimistic;
    }

	protected void setId(Long id) {
		this.id = id;
	}

	protected void setOptimistic(Integer optimistic) {
		this.optimistic = optimistic;
	}

	@Override
	public boolean equals(final Object other) {
		if (!(other instanceof AutoIDEntity))
			return false;
		AutoIDEntity castOther = (AutoIDEntity) other;
		return new EqualsBuilder().append(id, castOther.getId()).isEquals();
	}

	@Override
	public int hashCode() {
		return new HashCodeBuilder().append(id).toHashCode();
	}


}

[b]User类[/b][size=small][/size]
@Entity
@org.hibernate.annotations.Cache(usage = org.hibernate.annotations.CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
@SequenceGenerator(
	name="SEQ_STORE",
	sequenceName="user_id_sequence"
)
public class User  extends AutoIDEntity {

    /**
     * 登录名
     */
    private String userName;
    /**
     * 密码
     */
    private String password;
    /**
     * 角色集合
     */
    private Set<Role> roles = new HashSet<Role>();
  

    @ManyToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "ROLES2USERS",
    		joinColumns =  {
        		@JoinColumn(name = "USERS_FK", nullable = false, insertable = true, updatable = true, columnDefinition = "BIGINT")
    		},
    		inverseJoinColumns =  {
        		@JoinColumn(name = "ROLES_FK", nullable = false, insertable = true, updatable = true, columnDefinition = "BIGINT")
    		}
    	)
    public Set<Role> getRoles() {
        return this.roles;
    }
//省略getter和setter方法
}

[b]角色实体[/b][size=medium][/size]
@Entity
@org.hibernate.annotations.Cache(usage = org.hibernate.annotations.CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
@SequenceGenerator(
	name="SEQ_STORE",
	sequenceName="role_id_sequence"
)
public class Role extends AutoIDEntity {
    /**
     * 角色名
     */
    private String name;

    /**
     * 用户集合
     */
    private Set<User> users = new HashSet<User>();

    /**
     * 该角色的状态，1为有效，0为无效
     */
    private boolean active = true;
    
    @ManyToMany(fetch = FetchType.LAZY,mappedBy="roles")
	public Set<User> getUsers() {
		return users;
   }
  //省略其它的getter和setter方法
  
}