how to update data via list in Struts2

[namehas beentaken]

Hi, everyone. I am new to Struts2, and I am trying to build a phone bill calcualte page. I use list to contain and successfully display them in the text fileds in jsp page. however, when I modify the data and submit, the action class does not catch anything and the list become null. Can anyone help me through it?
First, I declear a class PhoneMember which has my own attributes. (name, extra minutes cost ...) all of them are String type.
then, In action class I define the list and setter/getter

private List<PhoneMember> phoneList;
public List<PhoneMember> getPhoneList(){
		return this.phoneList;
	}
public void setPhoneList(List<PhoneMember> aList){
		this.phoneList = aList;
	}

then I initial 5 elements and add them in the list. I also define a String parameter "total" for total cost.
later in jsp page, I use iterator

<s:form action="/PhoneCalculate.action" method="post">
    <table border="1">
      <s:iterator value="phoneList" status="ind" >
			<tr>
			 	<td><s:textfield name="phoneList[%{#ind.index}].name" value="%{name}" theme="simple" /></td>
				<td><s:textfield name="phoneList[%{#ind.index}].extraMin" value="%{extraMin}" theme="simple"/></td>
	        </tr>
			</s:iterator>
		</table>
		<s:textfield name="total"></s:textfield>  
	<s:submit></s:submit>	
	</s:form>

the initial value displayed successfully, but when I click the submit button, the phoneList in action class is null. all the data have been lost. But the "total" parameter receives the value;
Can any one helps me to solve this problem? I googled but can't find a solution. I also tried define another list in the action class and use that list name in the iterator. But neither lists get the data. Thanks very much

[Nitin Surana]

This example exactly does what you want.

http://www.onlinexamples.com/showfullexample.action?idexamples=11&title=Iterator%20over%20an%20array/list%20of%20objects/beans

Advanced Example

http://www.onlinexamples.com/showfullexample.action?idexamples=10&title=Nested%20Iterators%20Example

[namehas beentaken]

Thanks for the help, Nitin. Finally I find the reason, it is necessary to define an empty constructor in bean file.