Hibernate : Lob : To persist large text

From previous posts, you may observe String data type is mapped to varchar(255) by default. It is sufficient many times. But what if you need to store thousands of characters to persist, you should specify hibernate, hey hibernate I want this field to be treated as large object. You can do this by using “Lob” Annotation.

Lob annotation specifies that a persistent property or field should be persisted as a large object to a database-supported large object type.   

package myFirstHibernate;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

import java.util.Date;

@Entity
public class Employee {
 @Id
 @Column(name="emp_id")
 private int id;
 
 private String firstName;
 private String lastName;
 private String designation;
 private int age;
 private double salary;
 
 @Lob
 private String description;

 public int getId() {
  return id;
 }

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

 public String getFirstName() {
  return firstName;
 }

 public void setFirstName(String firstName) {
  this.firstName = firstName;
 }

 public String getLastName() {
  return lastName;
 }

 public void setLastName(String lastName) {
  this.lastName = lastName;
 }

 public String getDesignation() {
  return designation;
 }

 public void setDesignation(String designation) {
  this.designation = designation;
 }

 public int getAge() {
  return age;
 }

 public void setAge(int age) {
  this.age = age;
 }

 public double getSalary() {
  return salary;
 }

 public void setSalary(double salary) {
  this.salary = salary;
 }

 public String getDescription() {
  return description;
 }

 public void setDescription(String description) {
  this.description = description;
 }
 
}

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>
  
   <!--  Database Connection settings -->
    <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="connection.url">jdbc:mysql://localhost/sample</property>
    <property name="connection.username">root</property>
    <property name="connection.password">tiger</property>
    
    <!-- Enable the logging of all the generated SQL statements to the console -->
    <property name="show_sql">true</property>
    
    <!-- Format the generated SQL statement to make it more readable, -->
    <property name="format_sql">false</property>
    
    <!-- Hibernate will put comments inside all generated SQL statements to hint what’s the generated SQL trying to do -->
    <property name="use_sql_comments">false</property>
    
    <!-- This property makes Hibernate generate the appropriate SQL for the chosen database. -->
    <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
    
    <!-- Drop and re-create the database schema on startup -->
    <property name="hbm2ddl.auto">create</property>
    
    <!-- mappings for annotated classes -->
    <mapping class="myFirstHibernate.Employee" />
    
  </session-factory>
  
</hibernate-configuration>

package myFirstHibernate;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import java.util.Date;

public class TestEmployee {
 
 /* Step 1: Create session factory */
 private static SessionFactory getSessionFactory() {
  Configuration configuration = new Configuration().configure();
  StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder().
  applySettings(configuration.getProperties());
  SessionFactory factory = configuration.buildSessionFactory(builder.build());
        return factory;
    }
 
 public static void main(String args[]){
  Employee emp1 = new Employee();
  emp1.setAge(26);
  emp1.setDesignation("Senior Software Developer");
  emp1.setFirstName("Hari Krishna");
  emp1.setId(1);
  emp1.setLastName("Gurram");
  emp1.setSalary(80000);
  emp1.setDescription("Whaterver the world i saw yesterday is absolutely different from today");
  
  SessionFactory sessionFactory = getSessionFactory();
  Session session = sessionFactory.openSession();
  session.beginTransaction();
  session.save(emp1);
  session.getTransaction().commit();
  session.close();  
 }
}

Run TestEmployee class, you will get below kind of output in console.

Hibernate: drop table if exists Employee
Hibernate: create table Employee (emp_id integer not null, age integer not null, description longtext, designation varchar(255), firstName varchar(255), lastName varchar(255), salary double precision not null, primary key (emp_id))
Dec 20, 2014 7:35:27 AM org.hibernate.tool.hbm2ddl.SchemaExport execute
INFO: HHH000230: Schema export complete
Hibernate: insert into Employee (age, description, designation, firstName, lastName, salary, emp_id) values (?, ?, ?, ?, ?, ?, ?)

As you observe the output, column description treated as type “longtext”. It may vary from the database you are using. In MySQL, “longtext” can able to hold 4GB (4,294,977,295 bytes).

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