Hibernate的failed to lazily initialize a collection of role问题

我的pojo是：
 HumanInnerTrain.java:
private Long fid;
private String sheetName;
private String recordSn;
private String beginDate;
private String endDate;
private String trainPlace;
private String trainTeacher;
private String checkMethod;
private String trainTopic;
private String trainContent;
private String trainFiles;
private String operateUser;
private String operateDate;
private String re;
@SuppressWarnings("unchecked")
private Set humanInnerUserses = new HashSet(0);HumanInnerUsers.java:
private Long fid;
private HumanInnerTrain humanInnerTrain;
private Integer userid;
private String userName;
private String trainResult;
private String re;HumanInnerTrain.hbm.xml:<hibernate-mapping>
    <class name="cn.rhui.tech.human.vo.HumanInnerTrain" table="HUMAN_INNER_TRAIN" schema="dbo" catalog="special_platform">
        <id name="fid" type="java.lang.Long">
            <column name="FID" />
            <generator class="native" />
        </id>
        <property name="sheetName" type="java.lang.String">
            <column name="SHEET_NAME" length="80" />
        </property>
        <property name="recordSn" type="java.lang.String">
            <column name="RECORD_SN" length="25" />
        </property>
        <property name="beginDate" type="java.lang.String">
            <column name="BEGIN_DATE" length="20" />
        </property>
        <property name="endDate" type="java.lang.String">
            <column name="END_DATE" length="20" />
        </property>
        <property name="trainPlace" type="java.lang.String">
            <column name="TRAIN_PLACE" length="40" />
        </property>
        <property name="trainTeacher" type="java.lang.String">
            <column name="TRAIN_TEACHER" length="30" />
        </property>
        <property name="checkMethod" type="java.lang.String">
            <column name="CHECK_METHOD" length="40" />
        </property>
        <property name="trainTopic" type="java.lang.String">
            <column name="TRAIN_TOPIC" length="250" />
        </property>
        <property name="trainContent" type="java.lang.String">
            <column name="TRAIN_CONTENT" />
        </property>
        <property name="trainFiles" type="java.lang.String">
            <column name="TRAIN_FILES" length="200" />
        </property>
        <property name="operateUser" type="java.lang.String">
            <column name="OPERATE_USER" length="20" />
        </property>
        <property name="operateDate" type="java.lang.String">
            <column name="OPERATE_DATE" length="25" />
        </property>
        <property name="re" type="java.lang.String">
            <column name="REMARK_" length="150" />
        </property>
        <set name="humanInnerUserses" inverse="true" cascade="all" lazy="false" >
            <key>
                <column name="PARENTID_" />
            </key>
            <one-to-many class="cn.rhui.tech.human.vo.HumanInnerUsers" />
        </set>
    </class>
</hibernate-mapping>
HumanInnerUsers.hbm.xml<hibernate-mapping>
    <class name="cn.rhui.tech.human.vo.HumanInnerUsers" table="HUMAN_INNER_USERS" schema="dbo" catalog="special_platform" lazy="false">
        <id name="fid" type="java.lang.Long">
            <column name="FID" />
            <generator class="native" />
        </id>
        <many-to-one name="humanInnerTrain" class="cn.rhui.tech.human.vo.HumanInnerTrain" fetch="select" cascade="all" >
            <column name="PARENTID_" not-null="true"/>
        </many-to-one>
        <property name="userid" type="java.lang.Integer">
            <column name="USERID" />
        </property>
        <property name="userName" type="java.lang.String">
            <column name="USER_NAME" length="40" />
        </property>
        <property name="trainResult" type="java.lang.String">
            <column name="TRAIN_RESULT" length="40" />
        </property>
        <property name="re" type="java.lang.String">
            <column name="REMARK_" length="200" />
        </property>
    </class>
</hibernate-mapping>业务逻辑是:String hql =" from HumanInnerTrain";
List list = getBaseService().selectValueObjectsByHQL(hql);
Iterator ite =  list.iterator();
HumanInnerTrain humanInnerTrain = (HumanInnerTrain)ite.next();
Hibernate.initialize(humanInnerTrain);
Set set = humanInnerTrain.getHumanInnerUserses();
     HumanInnerUsers humanInnerUsers = (HumanInnerUsers) set.iterator().next();
     {
     String userName = humanInnerUsers.getUserName();
     System.err.println("=========================== userName= =====================" + humanInnerUsers.getUserName());
     }为会出现这个错误呢：failed to lazily initialize a collection of role: cn.rhui.tech.human.vo.HumanInnerTrain.humanInnerUserses, no session or session was closed 请教教我