怎么在Struts2中利用OGNL表达式对map进行遍历

package com.zx.demo.action;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import com.opensymphony.xwork2.ActionSupport;import com.zx.demo.model.Product;import com.zx.demo.model.Student;public class MapAction extends ActionSupport{   private Map<String,String> map; private Map<String,Student> studentMap; private Map<String,String[]> arrayMap; private Map<String,List<Student>> listMap;   //这里省略get set方法 public String testMap(){  map=new HashMap<String,String>(); map.put("1", "one"); map.put("2", "two");studentMap=new HashMap<String,Student>();studentMap.put("student1",new Student(new Long(1),"20034140201","张三1","男",25));studentMap.put("student2",new Student(new Long(2),"20034140202","张三2","女",26));studentMap.put("student3",new Student(new Long(3),"20034140202","张三3","男",27));arrayMap=new HashMap<String,String[]>();arrayMap.put("arr1", new String[]{"1","2003401","leejie","male","20"});arrayMap.put("arr2", new String[]{"2","2003402","huanglie","male","25"});arrayMap.put("arr3", new String[{"3","2003403","lixiaoning","male","21"});listMap=new HashMap<String,List<Student>>();  List<Student> list1=new ArrayList<Student>();list1.add(new Student(new Long(1),"20034140201","张三1","男",25));list1.add(new Student(new Long(2),"20034140202","张三2","男",25));list1.add(new Student(new Long(3),"20034140203","张三3","男",25));  listMap.put("class1", list1); List<Student> list2=new ArrayList<Student>();list2.add(new Student(new Long(1),"20034140301","李四1","男",20));list2.add(new Student(new Long(2),"20034140302","李四2","男",21));list2.add(new Student(new Long(3),"20034140303","李四3","男",22));list2.add(new Student(new Long(4),"20034140304","李四4","男",23));  listMap.put("class2", list2);return SUCCESS;    }  }