Hibernate中的关系映射，最常见的关系映射之一就是多对多关系映射例如用户与角色的关系，一个用户对应多个角色，一个角色对应多个用户。如图：

Hibernate中如何来映射这两个的关系呢？

下面就为大家讲解一下：

1、创建实体类User和实体类Role

User.java

package com.bjpowernode.hibernate;

import java.util.Set;

public class User {

	private int id;

	private String name;

	private Set roles;

	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 Set getRoles() {

		return roles;

	}

	public void setRoles(Set roles) {

		this.roles = roles;

	}

}

Role.java

package com.bjpowernode.hibernate;

public class Role {

	private int id;

	private String name;

	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;

	}

2、创建映射文件User.hbm.xml和Role.hbm.xml

User.hbm.xml

<?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>

	<class name="com.bjpowernode.hibernate.User" table="t_user">

		<id name="id">

			<generator class="native"/>

		</id>

		<property name="name"/>

		<set name="roles" table="t_user_role">

			<key column="user_id"/>

			<many-to-many class="com.bjpowernode.hibernate.Role" column="role_id" />

		</set>

	</class>

</hibernate-mapping>

Role.hbm.xml

<?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>

	<class name="com.bjpowernode.hibernate.Role" table="t_role">

		<id name="id">

			<generator class="native"/>

		</id>

		<property name="name"/>

	</class>

</hibernate-mapping>

3、效果图