public class Teacher{
     private String teacher_name;
     private List<Student> students;
}public class Student{
     private String student_name;
}List<Teacher>  teachers=new ArrayList<Teacher>();<s:iterator value="#session.teachers">
      <s:property value="#session.teachers.size()"/>     //老师的集合大小可以得到
      <s:iterator value="students">
           <s:property value="student_name"/>      //学生的名字可以得到
            <s:property value="students.size()"/>    //得不到学生集合的大小  请 怎么得到
       </s:iterator>
</s:iterator>