datepicker plugin of jQuery does not send the value to backend in Struts 2

I am using jQuery to show calendar, it perfectly work but when I submit the form backend does not receive the result >> result is null.

    <link rel="stylesheet" href="//code.jquery.com/ui/1.10.4/themes/smoothness/jquery-ui.css">
    <script src="//code.jquery.com/jquery-1.10.2.js"></script>
    <script src="//code.jquery.com/ui/1.10.4/jquery-ui.js"></script>
    <link rel="stylesheet" href="/resources/demos/style.css">
    <script>
        $(function() {
            $("#datepicker").datepicker();
        });

JSP:

   ...
   <s:textfield id="datepicker" name="datepicker"/>
   ...

Java:

  private String datepicker; 

  public String getDatepicker() {
      return datepicker;
  } 

  public void setDatepicker(String datepicker) {
     this.datepicker = datepicker;
  }

Generated HTML:

<input type="text" id="datepicker" value="" name="datepicker" class="hasDatepicker">

The value is empty for your textfield, so you might try to set the value

<s:textfield id="datepicker" name="datepicker" value="%{datepicker}"/>

and make sure the params interceptor is configured to the action that submits the form enclosed the textfield above.