JPA and Hibernate Introduction
Imagine you have a library with books. You need to keep track of each book's title, author, and location. You could write everything in a notebook (like JDBC), but it would be messy. Instead, you use a catalog system where each book has a card with all its details (like JPA).
JPA (Java Persistence API) is a specification – a set of rules – for mapping Java objects to database tables. Hibernate is the most popular implementation of JPA (like a brand that follows those rules).
ORM (Object-Relational Mapping) is the concept of mapping Java objects to database tables. Each table row becomes a Java object, and each column becomes a field.
Here is a simple JPA entity:
@Entity
@Table(name = "students")
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(name = "student_name", nullable = false)
private String name;
@Column(unique = true)
private String email;
private int age;
// constructors, getters, setters
}
Key JPA Annotations:
- @Entity – marks class as a JPA entity (maps to a table).
- @Table – specifies table name (optional, defaults to class name).
- @Id – marks the primary key.
- @GeneratedValue – how the ID is generated (AUTO, IDENTITY, SEQUENCE).
- @Column – column details (name, nullable, unique, length).
To use JPA with Spring, you need to configure EntityManagerFactory:
@Configuration
@EnableTransactionManagement
public class JpaConfig {
@Bean
public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();
em.setDataSource(dataSource());
em.setPackagesToScan("com.example.entity");
HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
vendorAdapter.setDatabasePlatform("org.hibernate.dialect.MySQL8Dialect");
vendorAdapter.setShowSql(true);
em.setJpaVendorAdapter(vendorAdapter);
return em;
}
@Bean
public PlatformTransactionManager transactionManager() {
JpaTransactionManager transactionManager = new JpaTransactionManager();
transactionManager.setEntityManagerFactory(entityManagerFactory().getObject());
return transactionManager;
}
}
Two Minute Drill
- JPA is a specification for mapping Java objects to database tables.
- Hibernate is the most popular JPA implementation.
- ORM = Object-Relational Mapping – the concept behind JPA.
- Use @Entity to mark a class as a database table.
- @Id marks the primary key, @Column defines column properties.
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