对象深度拷贝.(性能)

rack 对象结构
    List<shelf> shelfs;
    ......
 
shelf 对象结构
   List <port> ports;  大约5000个对象.
   ......

public static List copy(Object oldObject, int count) throws RuntimeException {
List<Object> list = new ArrayList<Object>();

converter = new XStream(new DomDriver());
String serial = converter.toXML(oldObject);
for (int i = 0; i < count; i++) {
     list.add(converter.fromXML(serial));
}
return list;
}

对机架对象做深拷贝..内存溢出．．
求：　有没有比这个性能更好的方法．．