Hibernate注解开发步骤

在编写Hibernate的时候，需要将实体类映射到数据库中的表。通常需要一个配置文件(hibernate.cfg.xml)，一个实体类(XX.java)，还有一个映射文件(XX.hbm.xml)。从JAVA5.0之后，可以利用注解来简化配置。简单来说就是不再需要映射文件了，hibernate需要的元数据(metadata)通过注解实体类就行了。

 

下面是一个简单的基于注解映射的Hibernate Hello World项目：

 

用到的工具和技术：1.Eclipse4.2.2

     hibernate-annotations.jar 

           hibernate-commons-annotations.jar (Hibernate中支持注解开发的jar包) 

            ejb3-persistence.jar(API规范的jar包) 

             slf4j/slf4j-api-1.5.0.jar 
             slf4j-log4j12-1.5.0.jar 
             log4j-1.2.15.jar  （支持日志输出的jar包，注意版本的匹配） 

 

首先是项目的整体架构：

 

项目的依赖(pom.xml):

 

<dependencies>
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>3.8.1</version>
    <scope>test</scope>
  </dependency>
  <dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>4.2.2.Final</version>
  </dependency>
</dependencies>

JPA jar包在hibernate3.6之后被放入hibernate-core包中。

 

 

Hibernate的配置文件(hibernate.cfg.xml):

 

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>

        <!-- Database connection settings -->
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/test</property>
        <property name="connection.username">username</property>
        <property name="connection.password">password</property>


        <!-- SQL dialect -->
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>


        <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>
        <!-- Drop and re-create the database schema on startup -->
        <property name="hbm2ddl.auto">update</property>

        <mapping class="org.hibernate.test.tutorial.Person" />
    </session-factory>

</hibernate-configuration>

注意：需要在Mysql数据库中创建一个test数据库 CREATE DATABASE test

 

 

一个简单的实体类:

 

package org.hibernate.test.tutorial;

import java.io.Serializable;
import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Entity
@Table(name="T_PERSONS")
public class Person implements Serializable {

    private static final long serialVersionUID = 1L;

    private Long id;
    private String name;
    private double age;
    private Date birth;

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="ID",unique=true)
    public Long getId() {
        return id;
    }

    @SuppressWarnings("unused")
    private void setId(Long id) {
        this.id = id;
    }

    @Column(name="NAME",length=20)
    public String getName() {
        return name;
    }

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

    @Column(name="AGE")
    public double getAge() {
        return age;
    }

    public void setAge(double age) {
        this.age = age;
    }

    @Temporal(TemporalType.DATE)
    @Column(name="BIRTH_DATE")
    public Date getBirth() {
        return birth;
    }
    public void setBirth(Date birth) {
        this.birth = birth;
    }

}

注意需要在Hibernate配置文件中注册该实体类： <mapping class="org.hibernate.test.tutorial.Person" />

 

 

最后编写一个运行程序：

 

public static void main( String[] args )
{
    SessionFactory factory = new AnnotationConfiguration().configure().buildSessionFactory();
    Session session = factory.openSession();

    session.beginTransaction(); // 开启事务

    try{
    Person p = new Person();
    p.setName("Benson");
    p.setAge(22);
    p.setBirth(new Date());

    session.save(p);
    } catch(Exception e) {
        e.printStackTrace();
        session.getTransaction().rollback();    // 回滚事务
    }

    session.getTransaction().commit();  // 提交事务
}

运行之后，可以在Ecilpse控制台观察到Hibernate为我们自动生成的格式化后的SQL:

 

 

Hibernate:
    insert
    into
        T_PERSONS
        (AGE, BIRTH_DATE, NAME)
    values
        (?, ?, ?)

进入Mysql控制台，可以查看到自动生成(hibernate.hbm2dll.auto)的表和插入的记录。