update a complex object through struts2

[maven apache]

Hi:

I meet some problem when I use struts as the mvc framework in my app,

They are the core  classes:

*Task{
  private int id;
  private String name;

  private List<TaskStep> steps;
}

TaskStep{
  public int id;
  private String name;
  private Date startDate;
  private TaskStatus status;
  private List<Operator> operators;
}

Operator{
  private int id;
  private String name;

}

Enum TaskStatus{
  start,doing,completed
}*

So,a task objec has relationship with so many other objects, now I have a
page to update(modify) a speified task:

I can read each attribute of the task and display it in the page,but I do
not know when user modify something(for example,modify the name of or
add/remove some operators of one its step.

At this time,how to transfer these information to the server side and update
it in the db?

BTW,I use the hiberante as the dao.