@Entity
@Table(name = "A")
class A{

Integer id;
List<B> b;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
public Integer getId() {
	return id;
}
setId(Integer id){...}
setB(List<B> b){...}
@ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
	@JoinTable(name = "a_b", joinColumns = @JoinColumn(name = "a_id"), inverseJoinColumns = @JoinColumn(name = "b_id"))
	
getB(){...}
}

@Entity
@Table(name = "B")
class B{
Integer id;
List<A> a;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
public Integer getId() {
	return id;
}
setId(Integer id){...}
setA(List<A> a){...}
@ManyToMany(mappedBy = "b", fetch = FetchType.EAGER)
getA(){...}

}

		A a = aDao.findById(aId);
                B b = bDao.findById(bId);
		a.getB().add(b);
		aDao.update(a);
		

               A a = aDao.findById(aId);
               A a = aDao.findById(aId);
                B b = bDao.findById(bId);
		b.getA().add(a);
		bDao.update(b);

 
Session session = sessionFactory.getCurrentSession();
if (Id == null) {
	return null;
}
B b= (b) session.get(b.class, Id);
return b;

if (b == null) {
	return false;
}
session.update(b);

a.getB().add(b);
b.getA().add(a);
aDao.update(a);
bDao.update(b);

a.getB().add(b);
b.getA().add(a);