@Entity
class A
{
  @ManyToMany
  public Set<B> getBs() { .... };
}

@Entity
class B
{
  @ManyToMany(mappedBy="bs")
  public Set<A> getAs() { .... };
}

A a = session.get(...);
B b = session.get(...);
a.getBs().remove(b);

public class LoggedInterceptor extends EmptyInterceptor {
   
   @Override
    public boolean onSave( Object entity, Serializable id, Object[] state,
        String[] propertyNames, Type[] types ) throws CallbackException
    {
       System.out.println("A "+entity.getClass().getCanonicalName() + " was created.");
       return false;
    }
   
    @Override
    public boolean onFlushDirty( Object entity, Serializable id,
        Object[] currentState, Object[] previousState, String[] propertyNames,
        Type[] types )
    {
       System.out.println("A "+entity.getClass().getCanonicalName() + " was updated.");
       return false;
    }
   
    @Override
    public void onDelete( Object entity, Serializable id, Object[] state,
        String[] propertyNames, Type[] types )
    {
       System.out.println( "A " +entity.getClass().getCanonicalName() + " was deleted.");
    }

}

onCollectionUpdate(Object collection, Serializable key)

    @Override
    public void onCollectionUpdate(Object collection, Serializable key)
    {
       
       if (collection instanceof PersistentSet)
       {
          PersistentSet newValues = (PersistentSet) collection;          
          Object owner = newValues.getOwner();
          
          Set<?> oldValues = ((Map<?,?>) newValues.getStoredSnapshot()).keySet();
          
          System.out.println(owner + " had one of its collections changed.");
          System.out.println("The collection property is "+ newValues.getRole().replace(owner.getClass().getCanonicalName() + ".", "") );
          
          // find all objects that were added
          for (Object newValue : newValues)
          {
             if (!oldValues.contains(newValue))
             {
                System.out.println("A " + newValue + " was added.");
             }
          }
          
          // find all objects that were deleted
          for (Object oldValue : oldValues)
          {
             if (!newValues.contains(oldValue))
             {
                System.out.println("A " + oldValue + " was removed.");
             }
          }
          
       }
       
    }