struts和hibernate简单问题

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >

<hibernate-mapping package="com.myapp">

<class name="Book" table="book">

<id name="id" column="id" type="java.lang.Integer">

<generator class="increment"/>

</id>

<property name="title" column="title" type="java.lang.String" />

<property name="author" column="author" type="java.lang.String" />

<property name="borrowallowed" column="borrowallowed" type="java.lang.Short" not-null="true" />

<many-to-one name="customer" column="customer_fk" class="Customer" />

</class>

</hibernate-mapping>

customer类是这样的

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC