[求教]为什么我在使用HashCodeBuilder在one-to-many关系中出现Lazy异常

最近遇到一个奇怪的问题，我在实体类的基类中使用了org.apache.commons.lang.builder.HashCodeBuilder，然后在one-to-many关系映射(customer <---> order)中出现org.hibernate.LazyInitializationException: illegal access to loading collection异常。

小弟刚刚接触hibernate，这个问题找了两天才发现问题所在，但是仍然不知道为什么会这样，请大家不吝赐教。

环境：struts + hibernate3,  hibernate2也试验过
异常：
org.hibernate.LazyInitializationException: illegal access to loading collection
at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:341)
at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:86)
at org.hibernate.collection.PersistentSet.hashCode(PersistentSet.java:411)
at org.apache.commons.lang.builder.HashCodeBuilder.append(HashCodeBuilder.java:392)
at org.apache.commons.lang.builder.HashCodeBuilder.reflectionAppend(HashCodeBuilder.java:353)
at org.apache.commons.lang.builder.HashCodeBuilder.reflectionHashCode(HashCodeBuilder.java:327)
at org.apache.commons.lang.builder.HashCodeBuilder.reflectionHashCode(HashCodeBuilder.java:194)
at cz.model.BaseObject.hashCode(BaseObject.java:78)
at org.apache.commons.lang.builder.HashCodeBuilder.append(HashCodeBuilder.java:392)
at org.apache.commons.lang.builder.HashCodeBuilder.reflectionAppend(HashCodeBuilder.java:353)
at org.apache.commons.lang.builder.HashCodeBuilder.reflectionHashCode(HashCodeBuilder.java:327)
at org.apache.commons.lang.builder.HashCodeBuilder.reflectionHashCode(HashCodeBuilder.java:194)
at cz.model.BaseObject.hashCode(BaseObject.java:78)
at java.util.HashMap.hash(HashMap.java:261)...

Hibernate 3 和 2 都是这个异常
只是2的异常描述是：net.sf.hibernate.LazyInitializationException: cannot access loading collection

程序片断：
BO基类 cz.model.BaseObject

abstract public class BaseObject implements Serializable {	
	public BaseObject(){}
    ...	
    public String toString() {
        return ToStringBuilder.reflectionToString(this,
                ToStringStyle.MULTI_LINE_STYLE);
    }

    public boolean equals(Object o) {
        return EqualsBuilder.reflectionEquals(this, o);
    }

    //注释掉这个函数就不出现异常
    public int hashCode() {
        return HashCodeBuilder.reflectionHashCode(this);
    }

cz.model.Customer继承BaseObject

public class Customer extends BaseObject implements Serializable {
      ...
	}

cz.model.Order继承BaseObject

public class Order extends BaseObject implements Serializable {
      ...
	}

映射文件

Customer.hbm.xml

<?xml version="1.0" encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
                            "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
                            "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<hibernate-mapping>

    <class name="cz.model.Customer" table="CUSTOMERS">
        <id name="id" column="ID" type="long">
            <generator class="increment"/>
        </id>
      ...
    <set 
        name="orders"
        cascade="all-delete-orphan" 
        inverse="true"
        lazy="true">
        <key column="CUSTOMER_ID" />
        <one-to-many class="cz.model.Order"/>
     </set>  
    </class>
    
</hibernate-mapping>

Order.hbm.xml

<hibernate-mapping>

	<class name="cz.model.Order" table="ORDERS">

		<id name="id" type="long" column="ID">
			<generator class="increment" />
		</id>
                  ....
		<many-to-one name="customer" column="CUSTOMER_ID"
			class="cz.model.Customer" cascade="save-update"/>
	</class>
</hibernate-mapping>

DAO实现类中的方法

	public Customer getCustomerById(Long customerId) throws AppException {

		Session session = HibernateUtil.getSession();
		Transaction tx = null;
		try {
			tx = session.beginTransaction();
			Query query = session.createQuery("from Customer c where c.id=:id");
			query.setLong("id", customerId.longValue());
			Customer customer = (Customer)query.uniqueResult();
			Set orderset = customer.getOrders();


                            //在这里会抛出上面说的异常，如果在BaseObject.java中去掉
                                 //public int hashCode() 方法就会正常，这是为什么呢？？
			System.out.println("orderset size=" + orderset.size());

			tx.commit();

			return customer;

		} catch (Exception ex) {
			HibernateUtil.rollbackTransaction(tx);
			AppException.appError(ex).printStackTrace();
			throw AppException.appError(ex);
		} finally {
			
			HibernateUtil.closeSession(session);
		}
	}

请大家帮我解答一下这个问题，谢谢。