Sunday 27 November 2022

Hibernate 6: map a byte array to BLOB

By annotating a byte array with @Lob annotation, we can map a byte array to BLOB.

 

Example

@Lob
private byte[] arr1;

 

Find the below working application.

 

Step 1: Create new maven project ‘hibernate-byte-array-to-blob-demo’.

 

Step 2: Update pom.xml with maven dependencies.

 

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.sample.app</groupId>
	<artifactId>hibernate-byte-array-to-blob-demo</artifactId>
	<version>1</version>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

		<java.version>15</java.version>
		<maven.compiler.source>${java.version}</maven.compiler.source>
		<maven.compiler.target>${java.version}</maven.compiler.target>

	</properties>

	<dependencies>
		<dependency>
			<groupId>com.h2database</groupId>
			<artifactId>h2</artifactId>
			<version>2.1.214</version>
		</dependency>

		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-core</artifactId>
			<version>6.1.2.Final</version>
		</dependency>

		<dependency>
			<groupId>javax.persistence</groupId>
			<artifactId>javax.persistence-api</artifactId>
			<version>2.2</version>
		</dependency>


	</dependencies>
</project>

 

Step 3: Define Demo class.

 

Demo.java

 

package com.sample.app.entity;

import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import jakarta.persistence.Lob;
import jakarta.persistence.Table;

@Entity
@Table(name = "demo")
public class Demo {
	@Id
	private int id;

	@Lob
	private byte[] arr1;

	public Demo(int id, byte[] arr1) {
		this.id = id;
		this.arr1 = arr1;
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public byte[] getArr1() {
		return arr1;
	}

	public void setArr1(byte[] arr1) {
		this.arr1 = arr1;
	}

}

 

Step 4: Create hibernate.cfg.xml file under src/main/resources folder.

 

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>
		<!-- JDBC Database connection settings -->
		<property name="connection.driver_class">org.h2.Driver</property>
		<property name="connection.url">jdbc:h2:mem:test</property>
		<property name="connection.username">admin</property>
		<property name="connection.password">admin</property>
		<property name="connection.pool_size">1</property>

		<property name="dialect">org.hibernate.dialect.H2Dialect</property>
		<!-- Echo the SQL to stdout -->
		<property name="show_sql">true</property>
		<property name="format_sql">true</property>
		<property name="current_session_context_class">thread</property>
		<!-- Drop and re-create the database schema on startup -->
		<property name="hbm2ddl.auto">create-drop</property>
		
		<!-- dbcp connection pool configuration -->
		<property name="hibernate.dbcp.initialSize">2</property>
		<property name="hibernate.dbcp.maxTotal">10</property>
		<property name="hibernate.dbcp.maxIdle">5</property>
		<property name="hibernate.dbcp.minIdle">3</property>
		<property name="hibernate.dbcp.maxWaitMillis">-1</property>

		<!-- mappings for annotated classes -->
		<mapping class="com.sample.app.entity.Demo" />

	</session-factory>

</hibernate-configuration>

 

Step 5: Define main application class.

 

App.java
package com.sample.app;

import java.io.IOException;
import java.sql.SQLException;
import java.util.List;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

import com.sample.app.entity.Demo;

import jakarta.persistence.criteria.CriteriaBuilder;
import jakarta.persistence.criteria.CriteriaQuery;

public class App {
	private static final SessionFactory SESSION_FACTORY = buildSessionFactory();

	private static SessionFactory buildSessionFactory() {
		try {

			final StandardServiceRegistry standardRegistry = new StandardServiceRegistryBuilder()
					.configure("hibernate.cfg.xml").build();

			final Metadata metaData = new MetadataSources(standardRegistry).getMetadataBuilder().build();

			return metaData.getSessionFactoryBuilder().build();

		} catch (Throwable ex) {
			throw new ExceptionInInitializerError(ex);
		}

	}

	private static <T> List<T> loadAllData(Class<T> clazz, Session session) {
		final CriteriaBuilder builder = session.getCriteriaBuilder();
		final CriteriaQuery<T> criteria = builder.createQuery(clazz);
		criteria.from(clazz);
		return session.createQuery(criteria).getResultList();
	}

	public static void main(final String args[]) throws IOException, SQLException {
		String msg = "Hello World";
		byte[] data = msg.getBytes();

		Demo e1 = new Demo(1, data);

		try (final Session session = SESSION_FACTORY.openSession()) {
			session.beginTransaction();

			session.persist(e1);

			session.flush();
			session.getTransaction().commit();

			List<Demo> records = loadAllData(Demo.class, session);

			for (Demo record : records) {
				int id = record.getId();
				System.out.println("id : " + id);

				byte[] arr1 = record.getArr1();

				System.out.println("arr1 : " + new String(arr1));
			}
		}

	}
}

 

Total project structure looks like below.

 

 


Run App.java, you will see below messages in the console.

Aug 17, 2022 3:22:48 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate ORM core version 6.1.2.Final
Aug 17, 2022 3:22:48 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using built-in connection pool (not intended for production use)
Aug 17, 2022 3:22:48 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: Loaded JDBC driver class: org.h2.Driver
Aug 17, 2022 3:22:48 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001012: Connecting with JDBC URL [jdbc:h2:mem:test]
Aug 17, 2022 3:22:48 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {password=****, user=admin}
Aug 17, 2022 3:22:48 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Aug 17, 2022 3:22:48 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH10001115: Connection pool size: 1 (min=1)
Aug 17, 2022 3:22:49 PM org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl logSelectedDialect
INFO: HHH000400: Using dialect: org.hibernate.dialect.H2Dialect
Aug 17, 2022 3:22:49 PM org.hibernate.metamodel.internal.EntityInstantiatorPojoStandard resolveConstructor
INFO: HHH000182: No default (no-argument) constructor for class: com.sample.app.entity.Demo (class must be instantiated by Interceptor)
Hibernate: 
    
    drop table if exists demo cascade 
Aug 17, 2022 3:22:49 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@2ab26378] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Hibernate: 
    
    create table demo (
       id integer not null,
        arr1 blob,
        primary key (id)
    )
Aug 17, 2022 3:22:49 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@5115f590] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Hibernate: 
    insert 
    into
        demo
        (arr1, id) 
    values
        (?, ?)
Hibernate: 
    select
        d1_0.id,
        d1_0.arr1 
    from
        demo d1_0
id : 1
arr1 : Hello World

 

You can download complete working application from this link.



 

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