hibernate注解annotation入门了解

àì夳堔傛蜴生んèń 2022-06-12 09:51 169阅读 0赞

前面我们写了实体类之后，都会写一个对应的\*.hbm.xml配置文件，然后把这个配置文件关联到hibernate.cfg.xml中，其实hibernate还有另一种写法，来映射对象关系，那就是注解annotation，今天就来简单的先看一下注解怎么使用。

新建一个java项目，项目结构如下：

![Center][]

导入jar包和从官网上获取hibernate压缩包，可以参见《[*Hibernate环境搭建和配置*][Hibernate]》

新建一个实体类，在实体类中使用注解，代码如下：

package com.ghibernate.pojo;
    
    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;
    
    /**
     * entiry表示需要持久化的实体类
     * Table表示实体类所对应的表
     */
    @Entity
    @Table(name="t_book")
    public class Book {
    
    	//Id主键
    	@Id
    	//指定主键生成策略
    	@GeneratedValue(strategy=GenerationType.AUTO)
    	private int id ;
    	@Column(name="book_name")
    	private String name ;
    	@Column
    	private double price ;
    	private String author ;
    	private Date pubDate ;
    	
    	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 double getPrice() {
    		return price;
    	}
    	public void setPrice(double price) {
    		this.price = price;
    	}
    	public String getAuthor() {
    		return author;
    	}
    	public void setAuthor(String author) {
    		this.author = author;
    	}
    	public Date getPubDate() {
    		return pubDate;
    	}
    	public void setPubDate(Date pubDate) {
    		this.pubDate = pubDate;
    	}
    	
    	
    }

将这个实体类关联到hibernate.cfg.xml中，如：

<!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>
    	
    	<property name="connection.driver_class">
    		com.mysql.jdbc.Driver
    	</property>
    	<property name="connection.url">jdbc:mysql:///hibernate4</property>
    	<property name="connection.username">root</property>
    	<property name="connection.password">root</property>
    	
    	<property name="hibernate.dialect">
    		org.hibernate.dialect.MySQL5Dialect
    	</property>
    	
    	<property name="show_sql">true</property>
    	
    	<property name="format_sql">true</property>
    	
    	<property name="hbm2ddl.auto">update</property>
    	
    	<mapping class="com.ghibernate.pojo.Book" />
    
    </session-factory>
    </hibernate-configuration>

HibernateUtil代码：

package com.robert.util;
    
    import org.hibernate.Session;
    import org.hibernate.SessionFactory;
    import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
    import org.hibernate.cfg.Configuration;
    
    /**
     * hibernate工具类
     */
    public class HibernateUtil {
    
    	private static Configuration cfg = null;
    	private static SessionFactory factory = null;
    	private static Session session = null ;
    	
    	static {
    		init();
    	}
    
    	/**
    	 * 初始化获得Configuration和SessionFacroty对象
    	 */
    	public static void init() {
    		cfg = new Configuration().configure();
    		factory = cfg.buildSessionFactory(new StandardServiceRegistryBuilder()
    				.applySettings(cfg.getProperties()).build());
    	}
    
    	/**
    	 * 获得Session对象
    	 * @return
    	 */
    	public static Session getSession() {
    		if (factory != null){
    			return session = factory.openSession();
    		}
    		
    
    		init();
    		return session = factory.openSession();
    	}
    	
    	/**
    	 * 关闭Session
    	 */
    	public static void closeSession() {
    		if(session!=null && session.isOpen())
    			session.close();
    	}
    
    }

测试类HIbernateTest代码：

package com.ghibernate.test;
    
    import java.util.Date;
    
    import org.hibernate.Session;
    import org.hibernate.Transaction;
    import org.hibernate.cfg.Configuration;
    import org.hibernate.tool.hbm2ddl.SchemaExport;
    import org.junit.Test;
    
    import com.ghibernate.pojo.Book;
    import com.robert.util.HibernateUtil;
    
    public class HibernateTest {
    
    	@Test
    	public void testCreateDB() {
    		Configuration cfg = new Configuration().configure();
    		SchemaExport se = new SchemaExport(cfg);
    		// 第一个参数：是否生成ddl脚本
    		// 第二个参数：是否执行到数据库中
    		se.create(true, true);
    	}
    	
    	@Test
    	public void testSave() {
    		
    		Session session = HibernateUtil.getSession() ;
    		Transaction tx = session.beginTransaction() ;
    		
    		Book book = new Book() ;
    		book.setName("读者") ;
    		book.setPrice(5.6) ;
    		book.setAuthor("众人") ;
    		book.setPubDate(new Date()) ;
    		
    		session.save(book) ;
    		tx.commit() ;
    		HibernateUtil.closeSession();
    		
    	}
    
    }

使用Junit4运行testCreateDB，生成数据库表

控制台打印的sql语句：

drop table if exists t_book
    
        create table t_book (
            id integer not null auto_increment,
            author varchar(255),
            book_name varchar(255),
            price double precision,
            pubDate datetime,
            primary key (id)
        )

运行testSave（）方法，存入数据库表中的数据如图：

![Center 1][]

以上就是annotation的简单用法

[Center]: /images/20220612/4ab9e72e90d249829aa9f562e0e6cd60.png
[Hibernate]: http://blog.csdn.net/u011159417/article/details/75014665
[Center 1]: /images/20220612/2e205176b81448bda56742ce3cc51298.png