a.hbm.xml
<class name="com.xxx.bean.A"  table="A">
  <id name="id"  column="id" not-null="true"  type="String">
   <generate name="native"/>
  </id>
  <property  name="name"  column="table_name"  type="String"/>
</class>
b.hbm.xml
<class name="com.xxx.bean.B" table="B">
   <id name="id"  column="id"  not-null="true" type="String">
     <generate name="native"/>
   </id>
   <property  name="age"  column="age" type="String"/>
   <many-to-one name="A"  column="a.id" type="String"/>
</class>
hibernate.cfg.xml
<resource mapping="com/xxx/bean/b.hbm.xml"/>
<resource mapping="com/xxx/beam/a.hbm.xml"/>
hql 语句
from  B a where a.id = 1