Hibernate中Blob对象类型的使用

       使用Intellij IDEA创建Hibernate项目，目录结构如下：

       其中 assets/app.png 为将要存储的照片，src/hibernate.cfg.xml 为Hibernate的配置文件，Students为实体，Students.hbm.xml 为对象关系映射的配置文件，test目录下其中使用到的测试类为 StudentsTest 类，使用到junit进行测试。（其他两个与此次说明无关）

hibernate.cfg.xml（使用mysql数据库中名为 hibernate的数据库）

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="connection.username">root</property>
        <property name="connection.password"></property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <!-- 下面的 hibernate 指的是 数据库名，即所用的数据库 -->
        <property name="connection.url">jdbc:mysql:///hibernate?useUnicode=true&characterEncoding=UTF-8</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

        <property name="show_sql">true</property>
        <property name="format_sql">true</property>
        <!--<property name="hbm2ddl.auto">create</property>-->
        <property name="hbm2ddl.auto">update</property>


        <!-- getCurrentSession方式获取 session 时需要添加如下配置 -->
        <property name="hibernate.current_session_context_class">thread</property>

        <mapping resource="Students.hbm.xml"/>
        <!-- DB schema will be updated if needed -->
        <!-- <property name="hbm2ddl.auto">update</property> -->
    </session-factory>
</hibernate-configuration>

Students.java （使用picture属性存储Blob类型数据）

import java.sql.Blob;
import java.util.Date;

/**
 * Created by DreamBoy on 2016/5/15.
 */
//学生类
public class Students {
    //1. 必须为公有的类
    //2. 必须提供公有的不带参数的默认的构造方法
    //3. 属性私有
    //4. 属性setter/getter封装

    private int sid; //学号
    private String sname; //姓名
    private String gender; //性别
    private Date birthday; //出生日期
    private String address; //地址
    private Blob picture; //照片

    public Students() {
    }

    public Students(int sid, String sname, String gender, Date birthday, String address) {
        this.sid = sid;
        this.sname = sname;
        this.gender = gender;
        this.birthday = birthday;
        this.address = address;
    }

    public int getSid() {
        return sid;
    }

    public void setSid(int sid) {
        this.sid = sid;
    }

    public String getSname() {
        return sname;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public Blob getPicture() {
        return picture;
    }

    public void setPicture(Blob picture) {
        this.picture = picture;
    }

    @Override
    public String toString() {
        return "Students{" +
                "sid=" + sid +
                ", sname='" + sname + '\'' +
                ", gender='" + gender + '\'' +
                ", birthday=" + birthday +
                ", address='" + address + '\'' +
                '}';
    }
}

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

    <class name="Students" table="students">
        <id name="sid" type="int">
            <column name="sid"/>
            <!--<generator class="assigned"/>-->
            <generator class="native"/>
        </id>
        <property name="sname" type="java.lang.String">
            <column name="sname"/>
        </property>
        <property name="gender" type="java.lang.String">
            <column name="gender"/>
        </property>

        <!--使用 java.util.Date 类型，在数据库中字段的类型为 datetime（会出现时分秒）-->
        <!--<property name="birthday" type="java.util.Date">-->
        <!--使用 Hibernate 中的数据类型 date，在数据库中字段的类型为 date （就不会出现时分秒了）-->
        <property name="birthday" type="date">
            <column name="birthday"/>
        </property>
        <property name="address" type="java.lang.String">
            <column name="address"/>
        </property>

        <property name="picture" type="java.sql.Blob">
            <column name="picture"/>
        </property>
    </class>
</hibernate-mapping>

StudentsTest.java 测试类

import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.io.*;
import java.sql.Blob;
import java.sql.SQLException;
import java.util.Date;

/**
 * Created by DreamBoy on 2016/5/15.
 */
//测试类
public class StudentsTest {
    private SessionFactory sessionFactory;
    private Session session;
    private Transaction transaction;

    @Before
    public void init() {
        //创建配置对象
        Configuration config = new Configuration().configure();
        //创建服务注册对象
        ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
        //创建会话工厂对象
        sessionFactory = config.buildSessionFactory(serviceRegistry);
        //会话对象
        session = sessionFactory.openSession();
        //开启事务
        transaction = session.beginTransaction();
    }

    @After
    public void destory() {
        transaction.commit(); //提交事务
        session.close(); //关闭会话
        sessionFactory.close(); //关闭会话工厂
    }

    @Test
    public void testSaveStudents() {
        //生成学生对象
        //Students s = new Students(1, "张三丰", "男", new Date(), "武当山");
        Students s1 = new Students();
        //如果 Students.hbm.xml 映射配置文件设置了 主键native，mysql中主键自增长，即便你设置了主键的值，也是不起作用的
        s1.setSname("s1");
        s1.setGender("男");
        s1.setBirthday(new Date());
        s1.setAddress("汕头");

        Students s2 = new Students();
        s2.setSname("s2");
        s2.setGender("女");
        s2.setBirthday(new Date());
        s2.setAddress("广州");

        //session.save(s); //保存对象进入数据库
        session.save(s1);
        session.save(s2);
    }

    @Test
    public void testWriteBlob() throws IOException {
        Students s = new Students(1, "张三丰", "男", new Date(), "武当山");
        //先获得照片文件
        //File f = new File("d:" + File.separator + "boy.jpg");

        /*File directory = new File("");//参数为空
        String courseFile = directory.getCanonicalPath() ;
        System.out.println(courseFile);*/

        File f = new File("assets/app.png");
        //获得文件输入流
        InputStream input = new FileInputStream(f);
        //创建一个Blob对象
        Blob image = Hibernate.getLobCreator(session).createBlob(input, input.available());
        //设置照片属性
        s.setPicture(image);
        input.close();
        session.save(s);
    }

    @Test
    public void testReadBlob() throws SQLException, IOException {
        Students s = (Students) session.get(Students.class, 1); //主键为1的Studetns记录
        //获得Blob对象
        Blob image = s.getPicture();
        //获得照片输入流
        InputStream input = image.getBinaryStream();
        //创建输出流
        File f = new File("assets/dest.png");
        OutputStream output = new FileOutputStream(f);
        //创建缓冲区
        byte[] buff = new byte[input.available()];
        input.read(buff);
        output.write(buff);
        input.close();
        output.close();
    }
}

       主要测试方法有两个 testWriteBlob 和 testReadBlob，保存一条含blob类型的记录和读取一条记录中的picture字段的值，并存储为图片文件。

运行 testWriteBlob 测试方法：

       查看数据库（插入成功）：

       运行testReadBlob方法，读取 刚插入的记录 的picture字段的值，并保存成图片：

       我们可以看到，成功读取并生成了一张图片：