@Entity
@Table(name="USER")
public class User {

  @Id
  @GeneratedValue(strategy=GenerationType.IDENTITY)
  private Long id;

  @Column(name="USERNAME")
  private String username;

  @Column(name="PASSWORD")
  private String password;

  @OneToMany(mappedBy="user")
  private Set<UserRole> userRoles;

}

@Table(name="ROLE")
@Entity
public class Role {

  @Id
  @GeneratedValue(strategy=GenerationType.IDENTITY)
  private Long id;

  @Column(name="NAME")
  private String name;

  @OneToMany(mappedBy="role")
  private Set<UserRole> userRoles;
}

@Entity
@Table(name="USER_ROLE")
@IdClass(UserRolePK.class)
public class UserRole {

  @Id
  @Column(name="USER_ID",insertable=false,
                         updatable=false)
  private Long userId;

  @Id
  @Column(name="ROLE_ID",insertable=false,
                         updatable=false)
  private Long roleId;

  @ManyToOne
  @JoinColumn(name="USER_ID")
  private User user;

  @ManyToOne
  @JoinColumn(name="ROLE_ID")
  private Role role;

  @Column(name="ENABLED")
  private boolean enabled;
}

public class UserRolePK {

  private Long userId;
  private Long roleId;
}

emf2 = Persistence.createEntityManagerFactory("hacon_w");
        entityManager = (Session) emf2.createEntityManager().getDelegate();
        tx2 = entityManager.getTransaction();
        tx2.begin();
       
        User u = new User();
        u.setUsername("a");
        u.setPassword("a");
       
        Role r = new Role();
        r.setName("b");
       
        UserRole ur = new UserRole(u,r,true);
       
        entityManager.save(u);
        entityManager.save(r);       
        entityManager.save(ur);
       
        tx2.commit();
        entityManager.close();