1.每颗继承树三张表:Object,hbm

package com.bjpowernode.hibernate;

public class Animal {

	private int id;
	
	private String name;
	
	private boolean sex;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public boolean isSex() {
		return sex;
	}

	public void setSex(boolean sex) {
		this.sex = sex;
	}
}

package com.bjpowernode.hibernate;

public class Pig extends Animal {

	private int weight;

	public int getWeight() {
		return weight;
	}

	public void setWeight(int weight) {
		this.weight = weight;
	}
}

package com.bjpowernode.hibernate;

public class Bird extends Animal {

	private int height;

	public int getHeight() {
		return height;
	}

	public void setHeight(int height) {
		this.height = height;
	}
}

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.bjpowernode.hibernate">
	<class name="Animal" table="t_animal" lazy="false">
		<id name="id">
			<generator class="native"/>
		</id>
		<property name="name"/>
		<property name="sex"/>
		<joined-subclass name="Pig" table="t_pig">
			<key column="pid"/>
			<property name="weight"/>
		</joined-subclass>
		<joined-subclass name="Bird" table="t_bird">
			<key column="bid"/>
			<property name="height"/>
		</joined-subclass>
	</class>
</hibernate-mapping>