Hibernate实践

环境准备

开发环境: Intellij IDEA

本地mysql数据库

创建Project

新增项目，命名为 hibernate-demo

创建目录结构如下

hibernate-demo
	/src
		/main
			/java
			/resources	
		/test
			/java
			/resources	
	pom.xml

依赖项配置

pom.xml中配置如下依赖项

<dependencies>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.35</version>
    </dependency>

    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>5.0.0.CR1</version>
    </dependency>

    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.8.2</version>
        <scope>test</scope>
    </dependency>
</dependencies>

这里使用当前最新版的 Hibernate类库以及 MySql JDBC驱动，也添加junit用作单元测试

Core Hibernate O/RM Functionality » 5.0.0.CR1

MySQL Java Connector » 5.1.35

创建hibernate配置

在/src/main/resources目录下添加hibernate.cfg.xml配置文件，内容如下

<?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/ant_test?useUnicode=true&amp;charseterEncoding=UTF-8</property>
        <property name="connection.username">root</property>
        <property name="connection.password">123</property>

        <!-- JDBC connection pool (use the built-in) -->
        <!--<property name="connection.pool_size">1</property>-->

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

        <!-- Enable Hibernate's automatic session context management -->
        <property name="current_session_context_class">thread</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">create</property>

        <mapping resource="demo/Event.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

connection.driver_class指定为 Mysql jdbc驱动

connection.url设置数据库访问地址，指定数据库名，这里是ant_test

connection.username与connection.password顾名思义

关于连接池，Hibernate comes with support for two third-party open source JDBC connection pools: c3p0 and proxool

<property name="current_session_context_class">thread</property>

注意这里将current_session_context_class设置为 thread，后文有描述

<mapping resource="demo/Event.hbm.xml"/>关联类型映射文件，见后文

定义实体类

同官方文档，实现定义一个Event类型，我这里新增/src/main/java/demo包，其中添加Event.java

public class Event {
    private Long id;

    private String title;
    private Date date;

    public Event() {}

    public Long getId() {
        return id;
    }

    private void setId(Long id) {
        this.id = id;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }
}

可以注意到，这里setId方法访问权限设置为private，这是hibernate官方推荐的做法，id一般由hibernate来维护。hibernate通过反射可以访问方法与字段，即使设置了private与protected访问权限

定义映射文件

在/src/main/resources/demo中新增Event.hbm.xml:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="demo">
    <class name="Event" table="events">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="date" type="timestamp" column="date"/>
        <property name="title"/>
    </class>
</hibernate-mapping>

映射文件以类名称开头，以hbm.xml 结尾

创建工具类型HibernateUtility

官方文档中HibernateUtil创建SessionFactory的方式可能由于版本或者其他原因，在我的机器上测试无法正确加载hibernate配置数据，修正后，内容如下：

/**
 * Created by ant on 2015/7/5.
 */
public class HibernateUtility {
    private static final SessionFactory sessionFactory = buildSessionFactory();

    private static SessionFactory buildSessionFactory() {
        try {
            Configuration configuration = new Configuration().configure();
            configuration.addClass(Event.class);
            ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
                    .applySettings(configuration.getProperties()).build();
            return configuration.buildSessionFactory(serviceRegistry);
        }
        catch (Throwable ex) {
            // Make sure you log the exception, as it might be swallowed
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

The getCurrentSession() method always returns the “current” unit of work. Remember that we switched the configuration option for this mechanism to “thread” in our src/main/resources/hibernate.cfg.xml? Due to that setting, the context of a current unit of work is bound to the current Java thread that executes the application.

Important

Hibernate offers three methods of current session tracking. The “thread” based method is not intended for production use; it is merely useful for prototyping and tutorials such as this one. Current session tracking is discussed in more detail later on.

下面开始使用hibernate

在/src/main/java目录中新增入口类型Demo.java，内容如下:

/**
 * Created by ant on 2015/7/5.
 */
public class Demo {
    public static void main(String[] args) {
        Session session = HibernateUtility.getSessionFactory().getCurrentSession();
        session.beginTransaction();

        Event event = new Event();
        event.setTitle("hello hibernate");
        event.setDate(new Date());
        session.save(event);

        session.getTransaction().commit();

        System.out.println("done!");
    }
}

可以在集成开发环境中直接运行，将会自动在ant_test数据库中新增events表，同时将新插入一行数据

之所以可以自动构建表，是有与在hibernate.cfg.xml中做了如下设置

<property name="hbm2ddl.auto">create</property>

可以将该值修改为update

可以通过命令执行程序

编译:　mvn compile

执行: mvn exec:java -Dexec.mainClass="Demo"

可以通过-Dexec.args="arg"补充参数

参考

官方文档