Quick Start

Hibernate是java中常用的ORM框架，經常與Spring整合在一起
本文主要介紹單純的Hibernate，並以hibernate5為主

安裝

http://hibernate.org/orm/releases/5.0/

環境

• Hibernate是jdbc的封裝，須下載mysql-connector-java-8.0.12.jar
• Hibernate相依於jta，須下載jta-1.1.jar
• 其他的jar檔，在hibernate-release-5.0.12.Final.zip的lib/required/裡全部都有。

hibernate.cfg.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/testHibernate</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password"></property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
        <property name="hibernate.format_sql">true</property>
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.hbm2ddl.auto">update</property>

        <mapping class="my.model.Event"></mapping>
    </session-factory>
</hibernate-configuration>

說明:

• 新版jdbc路徑是com.mysql.cj.jdbc.Driver
• hibernate5的dialog建議使用org.hibernate.dialect.MySQL5Dialect

Session

Hibernate每次操作db時，需建立session。

// session factory
Configuration config = new Configuration().configure();
SessionFactory sessionFactory = config.buildSessionFactory();
// 操作db
Session session = sessionFactory.openSession();
session.beginTransaction();
session.saveOrUpdate(entity); 
session.getTransaction().commit();
session.close();

DAO

public class HibernateSessionManager {
    protected Session getSession() {
        // 仿照上方取得session
    }
}
public interface BaseDao<T> {
    public boolean insert(T entity);
    public List<T> list(T entity, Order order, int offset, int limit);
}
public class BaseDaoImpl<T> extends HibernateSessionManager implements BaseDao<T> {
    @Override
    public boolean insert(T entity) {
        getSession().saveOrUpdate(entity);
        return true;
    }

    @Override
    public List list(T entity, Order order, int offset, int limit) {
        Criteria c = getSession().createCriteria(entity.getClass());

        if(order != null) {
            c.addOrder(order);
        }
        if(offset > -1) {
            c.setFirstResult(offset);
        }
        if(limit > -1) {
            c.setMaxResults(limit);
        }
        return c.list();
    }
}
public interface EventDao extends BaseDao<Event> {
}
public class EventDaoImpl extends BaseDaoImpl<Event> implements EventDao {
}

說明

• BaseDao及BaseDaoImpl是Spring慣用的寫法：定義介面及實作，這裡也採用這樣的慣例。BaseDao代表的是共用的dao，所有的dao將繼承它。
• 最後操作db的是EventDaoImpl，實作EventDao介面。雖然目前沒有其他實作，但將來如果有針對Event這個table有特殊的操作，就可以擴充。

Entity

@Entity
@Table(name = "events")
public class Event {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(length = 128)
    private String name;

    @Column
    @Temporal(TemporalType.TIMESTAMP)
    private Date datetime;

    // getter,setter略
}

主程式

EventDao eventDao = new EventDaoImpl();
// insert
Date date = new Date();
Event e = new Event();
e.setName("name-" + date.getTime());
e.setDatetime(date);
eventDao.insert(e);    
// query
List<Event> list = eventDao.list(e, null, 0, 3);
for(Event x : list) {
    System.out.println("Event: " + x.getName());
}

完成整程式碼：
https://github.com/welson327/pure_hibernate