组件(Component)是一个被包含的对象，在持久化的过程中，它被当作值类型，而并非一个实体的引用。在这篇文档中，组件这一术语指的是面向对象的合成概念.
·user.java
package com.jason.component;
public class User{
private Integer id;
private String name;
private String password;
private Contact contact;
/**
* @return Returns the id.
*/
public Integer getId() {
return id;
}
/**
* @param id The id to set.
*/
public void setId(Integer id) {
this.id = id;
}
/**
* @return Returns the name.
*/
public String getName() {
return name;
}
/**
* @param name The name to set.
*/
public void setName(String name) {
this.name = name;
}
/**
* @return Returns the password.
*/
public String getPassword() {
return password;
}
/**
* @param password The password to set.
*/
public void setPassword(String password) {
this.password = password;
}
/**
* @return Returns the contact.
*/
public Contact getContact() {
return contact;
}
/**
* @param contact The contact to set.
*/
public void setContact(Contact contact) {
this.contact = contact;
}
}
· contact.java
package com.jason.component;
public class Contact {
private String email;
private String address;
/**
* @return Returns the address.
*/
public String getAddress() {
return address;
}
/**
* @param address The address to set.
*/
public void setAddress(String address) {
this.address = address;
}
/**
* @return Returns the email.
*/
public String getEmail() {
return email;
}
/**
* @param email The email to set.
*/
public void setEmail(String email) {
this.email = email;
}
}
· User.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<hibernate-mapping package="com.jason.component">
<class
name="User"
table="user"
>
<meta attribute="sync-DAO">false</meta>
<id
name="Id"
type="integer"
column="id"
>
<generator class="native"/>
</id>
<property
name="Name"
column="name"
type="string"
not-null="true"
length="20"
/>
<property
name="Password"
column="password"
type="string"
not-null="true"
length="20"
/>
<component class="Contact" name="Contact">
<property
column="email"
length="50"
name="Email"
not-null="false"
type="string"
/>
<property
column="address"
length="100"
name="Address"
not-null="false"
type="string"
/>
</component>
</class>
</hibernate-mapping>
package com.jason.component;
import java.util.List;
import java.util.ListIterator;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
public class testComponent {
public static void main(String[] args) throws HibernateException {
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
testInsert(sessionFactory);
testQuery(sessionFactory);
sessionFactory.close();
}
public static void testInsert( SessionFactory sessionFactory )throws HibernateException {
Session session = sessionFactory.openSession();
Transaction tx= session.beginTransaction();
User user = new User();
Contact contact=new Contact();
contact.setEmail("gm_jing@yahoo.com.cn");
contact.setAddress("beijing");
user.setName("gm_jing");
user.setPassword("1111111");
user.setContact(contact);
session.save(user);
tx.commit();
session.close();
System.out.println("OK！");
}
public static void testQuery( SessionFactory sessionFactory )throws HibernateException {
Session session = sessionFactory.openSession();
Transaction tx= session.beginTransaction();
User user = new User();
Query query=session.createQuery("from User as user");
//query.setCharacter(1, 'M');
List names =query.list();
for(ListIterator it=names.listIterator();it.hasNext();){
user= (User)it.next();
System.out.println("Id: " + user.getId());
System.out.println("name: " + user.getName());
System.out.println("password: " + user.getPassword());
if(user.getContact()!=null){
if(user.getContact().getEmail()!=null){
System.out.println("Email: " + user.getContact().getEmail());
}
if(user.getContact().getAddress()!=null){
System.out.println("Address: " + user.getContact().getAddress());
}
}
}
tx.commit();
session.close();
}
}
就像所有的值类型一样, 组件不支持共享引用。 换句话说，两个Contact可能相同，但是两个User对象应该包含两个独立的Contact对象，只不过这两个Contact对象具有“同样”的值。 组件的值可以为空，其定义如下。 每当Hibernate重新加载一个包含组件的对象,如果该组件的所有字段为空，Hibernate将假定整个组件为空。 在大多数情况下,这样假定应该是没有问题的。