我有两个类Role和Privilege，它们之间的关系是ManyToMany。当把Privilege添加到Role，然后调用saveOrUpdate(role)时，我会得到下面的异常。
下面是Role类：

@Entity
@Table(name = "ROLES")
public class Role implements GenericDomain {

    private static final long serialVersionUID = -7620550658984151796L;

    private Long    id;
    private String  code;
    private String  name;

    private Set<User> users = new HashSet<User>(0);
    private Set<Privilege> privileges = new HashSet<Privilege>(0);

    public Role() {
    }

    public Role(String code, String name) {
        this.code = code;
        this.name = name;
    }

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name = "ID")
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }

    @Column(name = "CODE", unique = true, nullable = false, length = 16)
    @NotEmpty(message= "password.required")
    @Length(min = 3, max = 16)
    public String getCode() { return code; }
    public void setCode(String code) { this.code = code; }

    @Column(name="NAME", nullable = false, length = 64)
    @NotEmpty
    @Length(min = 1, max = 32)
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }

    @ManyToMany(cascade=CascadeType.ALL)
    @JoinTable(name = "ROLES_PRIVILEGES"
        , joinColumns = { @JoinColumn(name = "ROLE_ID") }
        , inverseJoinColumns = { @JoinColumn(name = "PRIVILEGE_ID") }
    )

    public Set<Privilege> getPrivileges() {
        return this.privileges;
    }
    public void setPrivileges(Set<Privilege> privileges) {
        this.privileges = privileges;
    }
    /*  overide of hascode, equals*/ 
}

下面是Privilege类：

@Entity
@Table(name = "PRIVILEGES")
public class Privilege implements GenericDomain {

    private static final long serialVersionUID = 4649689934972816194L;

    private Long    id;
    private String  code;

    private Set<Role> roles = new HashSet<Role>(0);

    public Privilege() {
    }

    public Privilege(String code) {
        this.code = code;
    }

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name = "ID")
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }

    @Column(name = "CODE", unique = true, nullable = false, length = 16)
    @NotEmpty(message= "password.required")
    @Length(min = 3, max = 16)
    public String getCode() { return code; }
    public void setCode(String code) { this.code = code; }

    @ManyToMany(cascade=CascadeType.REFRESH, mappedBy="privileges")
    public Set<Role> getRoles() {
        return this.roles;
    }
    public void setRoles(Set<Role> roles) {
        this.roles = roles;
    }

    /*overide equals and hascode*/
}

这里有个例外：

IllegalArgumentException in class: com.stunaz.domain.Privilege, getter method of property: id
 ....
 javax.persistence.PersistenceException: org.hibernate.PropertyAccessException: IllegalArgumentException occurred calling getter of com.stunaz.domain.Privilege.id
 ....
 java.lang.IllegalArgumentException: object is not an instance of declaring class

似乎我的Map出了问题，在某个地方我应该传递一个对象，但我传递的是一个ID。