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 + '\'' +
'}';
}
}

Students.hbm.xml（注意使用Hibernate映射到数据库中所使用的类型）

<?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：