Hibernate

Key Features

• Object-Relational Mapping: Maps Java objects to database tables
• HQL (Hibernate Query Language): Object-oriented query language
• Lazy Loading: Loads data on-demand for better performance
• Caching: First-level and second-level caching mechanisms
• Transaction Management: Automatic transaction handling
• Database Independence: Works with multiple database systems

Entity Mapping Example

                        
@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    @Column(name = "username", unique = true, nullable = false)
    private String username;
    
    @Column(name = "email", unique = true, nullable = false)
    private String email;
    
    @Column(name = "created_at")
    @Temporal(TemporalType.TIMESTAMP)
    private Date createdAt;
    
    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private List<Order> orders = new ArrayList<>();
    
    // Constructors, getters, and setters
    public User() {}
    
    public User(String username, String email) {
        this.username = username;
        this.email = email;
        this.createdAt = new Date();
    }
    
    // Getters and setters...
}
                        
                    

Hibernate Configuration

                        
// hibernate.cfg.xml
<?xml version="1.0" encoding="UTF-8"?>
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">
            com.mysql.cj.jdbc.Driver
        </property>
        <property name="hibernate.connection.url">
            jdbc:mysql://localhost:3306/mydb
        </property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">password</property>
        <property name="hibernate.dialect">
            org.hibernate.dialect.MySQL8Dialect
        </property>
        <property name="hibernate.hbm2ddl.auto">update</property>
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.format_sql">true</property>
        
        <mapping class="com.example.User"/>
        <mapping class="com.example.Order"/>
    </session-factory>
</hibernate-configuration>
                        
                    

CRUD Operations

                        
public class UserDAO {
    private SessionFactory sessionFactory;
    
    public UserDAO(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
    }
    
    // Create
    public void saveUser(User user) {
        Session session = sessionFactory.getCurrentSession();
        session.beginTransaction();
        session.save(user);
        session.getTransaction().commit();
    }
    
    // Read
    public User getUserById(Long id) {
        Session session = sessionFactory.getCurrentSession();
        session.beginTransaction();
        User user = session.get(User.class, id);
        session.getTransaction().commit();
        return user;
    }
    
    // Update
    public void updateUser(User user) {
        Session session = sessionFactory.getCurrentSession();
        session.beginTransaction();
        session.update(user);
        session.getTransaction().commit();
    }
    
    // Delete
    public void deleteUser(Long id) {
        Session session = sessionFactory.getCurrentSession();
        session.beginTransaction();
        User user = session.get(User.class, id);
        if (user != null) {
            session.delete(user);
        }
        session.getTransaction().commit();
    }
    
    // HQL Query
    public List<User> getUsersByEmail(String email) {
        Session session = sessionFactory.getCurrentSession();
        session.beginTransaction();
        Query<User> query = session.createQuery(
            "FROM User u WHERE u.email LIKE :email", User.class);
        query.setParameter("email", "%" + email + "%");
        List<User> users = query.getResultList();
        session.getTransaction().commit();
        return users;
    }
}
                        
                    

Career Impact

Learning Path

1. Master Java fundamentals and object-oriented programming
2. Learn relational database concepts and SQL
3. Understand ORM principles and mapping strategies
4. Practice with Hibernate configuration and annotations
5. Explore HQL and Criteria API for querying
6. Implement caching and performance optimization
7. Integrate with Spring Framework and JPA